Pgurvfifru e... a 1.}: .v .121 . .. .23.! 2.“...2...‘ z.) i: 3.1.! ivy) a! 1:52.55) . 1“,“Y2‘V‘ 5.. “25:05). .12 :3... r 1;. Zflx 2V2. «. Erna...) 5; .12).; I . c. 1: ((43.12) .3). I f5...n use urea in dilution studies in cattle as a method for estimating body compostion. A distinct advantage of urea dilution as a marker is the minimal handling and single sampling time to arrive at an estimate of urea space (US). Several workers 23 (Preston and Koch, 1973: Bennett et al., 1975; Koch and Preston, 1979) examined the differences in urea equilibration times in blood and body water. They found urea and cellular water equilibration times to be optimal between 12 and 15 minutes post-injection. In recent studies (Bennett et al., 1982; Hammond, 1984:1988) sampling at 12 minutes post-infusion was used to determine US. Preston and Koch ( 1973) and Koch and Preston (1979) used carcass specific gravity as an index of composition with which to compare US composition estimates. They found high correlations (r2 > .68) between US, rib water, protein and fat and with carcass specific gravity. Comparisons of US dilution with noninvasive electronic measuring devices have been examined by Bennett et al. (1982) and Jones et al. (1982). Jones et al. (1982a) used ultrasonic measures of backfat thickness in lambs, mature cows and steers to compare them with US determinations of carcass lean. Their low correlations of r2 < .30 for lambs, r2 < .55 in cows and r2 < .14 in steers raised considerable doubt as to the effectiveness of this method. Bennett et al. (1982), on the other hand, found US to be a better predictor of composition than ultrasonic measurements in uniform animals, adjusted to constant weights. However, they concluded that ultrasonic measurements and US were equally reliable as indices of body composition over a wide range of breeds. 24 Meissner et al. (1980a,b,c) used urea and tritium to estimate body composition in young bulls. They found that tritium was more accurate in predicting body composition than US. When additional variables (i.e., body weight) were included, the reliability of US as a predictor of composition was increased. Bartle et al. (1983) examined the use of live weight US versus empty body weight in mature beef and dairy cows. US of live weight was poorly correlated with composition as determined In; specific gravity and 9-10-11 rib composition. However, empty body US correlations were improved for both types of animals. Further refinement of the multiple regression equations with inclusion of plasma urea-nitrogen (PUN) changes 2 = .66 and .62 for beef and improved correlations to r dairy types, respectively. Inclusion of initial PUN values improved correlations for dairy animals only. These studies indicate the usefulness of US dilution is improved when other independent variables are included in the multiple regression equations. Hammond et al., (1984,1988) recently evaluated the urea dilution technique by comparing US to actual direct measurement of empty body water in steers. They reported correlations of r2 > .96 between US and empty body water with multiple regression analysis. Inclusion of other independent variables predicted empty body water in similar ways. In general, these studies suggest urea dilution is a 25 useful method for estimating body composition. The most useful application of predicting composition by US, appears to be in conjunction with other variables in developing predictive multiple regression equations. Hydrogen Isotope Dilution. Since water comprises the largest component of the lean empty body, logic would suggest this ought to be the method of choice for measurements in growth and nutritional studies. Several hundred references report information and analyze the advantages, disadvantages and differences between deuterium oxide (D20) and tritiated water (TOH) in dilution studies. Water labeled with either D20 or tritium serves as an ideal tracer with which to measure water fluxes since they cross the barriers in the body at the same rate as body water (Pinson, 1952). The hydrogen isotope dilution technique was introduced by Hevesy and Hofer (1934) in studies in humans. Tritium, (t1/2 = 12.3 years), the radioactive isotope of hydrogen with the atomic mass of three, has been the favorite isotope for use until recently. Tritium has been relatively inexpensive and can be measured at low concentrations, especially with the increased sensitivity of liquid scintillation counters. However, the concerns with disposal costs and safety have limited the use of TOH in large animals. Deuterium (D2), 26 on the other hand, is a stable, nonradioactive isotope of hydrogen. Natural occurring concentration ratios of D2 to hydrogen are about 150 ppm. D2 combines with oxygen to form D20 which is about 10% denser than pure water. DZO has become the hydrogen isotope of choice in tracer studies of large animals even though it is relatively expensive. This increased cost is more than offset by the salvage value of the carcasses, otherwise lost in TOH studies. Also, improvements have been made in measuring sensitivity at low concentrations by Byers (1979a) and Zweens et al. (1980), with further modifications described by Ferrell and Philips (1980). Many authors have reviewed the use of the biological tracers to measure body water (Pinson, 1952: Widdowson and Dickerson, 1964; Panaretto, 1968; Ward and Johnson, 1972; Sheng and Huggins, 1979 and Nagy and Costa, 1980.). Lifson and McClintock (1966) list several assumptions made when using the labeled water method. These include: 1) constant body water volume, 2) constant water flux rates, 3) tritium only labels body water, 4) tritium leaves the body in the form of water, 5) the specific activity in water leaving a labeled animal is the same as that in the animal’s body water and 6) water in the environment does not enter animals through their skin or lung surfaces. Nagy and Costa (1980) evaluated these assumptions and concluded that although there are problems with each of these assumptions 27 and exaggerated values could result, the heavy water methods provide a reasonably accurate measure of body water. These findings are in general agreement with equations for isotope dilution analysis and validation presented by Gest et al. (1947) and Radin (1947). Pinson (1952) examined the use of 020 and tritium in water exchange studies and Edelman (1952) studied the relationship of D20 equilibration with body water. Because of the unique properties of both D20 and TOH, research workers have found exchanges of D2 with the hydrogen of water to generally overestimate body water both in pregnant ewes (Trigg et al., 1978) and in cattle (Robelin, 1982) and Arnold et al., (1985). Tritium has also been found to both overestimate (Sheng and Huggins, 1979: +4 to 15%) and underestimate (Donnelly and Freer, 1974: Trigg et al. 1978: -2.4%), body water. The use of these techniques for determining body composition in farm animals has been reviewed by Reid et al. (1955) and Pearson (1965). The majority of studies used D20 or TOH to determine total body water followed by estimates of body composition. TKHI has been 'used extensively in sheep (Till and Downes, 1962: Panaretto, 1963; Panaretto and Till, 1963: Panaretto, 1964; Reardon, 1969; Searle, 1970a,b,c; Smith and Sykes, 1974: Donnelly and Freer, 1974: Trigg et al., 1978) to determine either total water, body composition or both. Donnelly and Freer 28 (1974) used data collected from 149 Merino and Merino crossbred sheep to develop prediction equations for estimation of body composition. They found that inclusion of the variable, maturity, in the regression equations decreased residual standard deviations to a large enough degree so that the equations could be used across a wide range of ages. Searle (1970b) evaluated TOH space in 33 wethers as a predictive tool in previously published equations (Searle, 1970a). Refinement of the equations reduced variances of individual body components from the earlier study (Searle, 1970a) to the point that Searle proposed tritium dilution as a reliable method to measure body composition from 3 days of age to the adult stage in sheep. Furthermore, Trigg et al. (1978), although finding TOH space to underestimate body water by 2.4%, stated the results for body composition were more precise than those obtained by either 42K dilution or D20 techniques. In cattle, TOH space has been used to estimate body water and composition by Carnegie and Tulloh (1968), Meissner et al. (1980a,b,c), Chigaru and Topps (1981), Little and McLean (1981). Meissner et al. (1980a,b,c) physically separated the body components of 20 cattle and performed chemical analysis. TOH could be used to estimate water, protein and ash, but the variation at 400 kg live weight ranged from 4 to 10%. However, ether extract showed a 25 to 30% variance with that predicted from TOH space. 29 Little and McLean (1981) also dissected and analyzed the whole body components of TOH infused animals, using chemical analysis and TOH space to derive equations. They included gut water as a part of whole body weight. Correlation coefficients between actual and predicted values for total body water (TBW), total body fat (TBF) and total body protein (TBP) were .984, .997 and .956, respectively. They indicated that, since TBW was being estimated, it is important to accurately measure fasted live weight (FLW), which includes gut water, immediately before slaughter. Accurate measures of FLW are closely related to the sum of TBW plus TBF along with TBP. They found, as did Haecker (1920) and Foot and Tulloh (1977), that gut contents were 87% water with the total dry matter in the gut being 1.75% of FLW. Suggestions of the need for further research into repeated measurements of body water in the same animal, to quantify body composition differences between animals is supported by these data and others. In early studies with 020 in sheep (Till and Downes, 1962: Foot and Greenhalgh, 1970: Farrell and Reardon, 1972: Trigg et al. 1978) and cattle (Little and Morris, 1972: Crabtree et al., 1974: Robelin, 1977), body water space was treated as a single pool including both actual body water and gut water as one component. This extra gut water, which is not related to any gut or carcass tissues, can 30 fluctuate on the average from 3 to 5 % or more per day due to dietary, environmental and animal differences (Nagy and Costa, 1980: Robelin, 1982). This variation can introduce substantial error in predictions of total body water if not accounted for. Crabtree et al. (1974) found high correlations between D20 space (DS), fat-free mass and empty body water (EBW) in six Fresian (F) and six F x Hereford steers. Robelin (1982) used a similar approach, with some modification, when he attempted to estimate gut content and correct for it in the final equation. He found a high correlation between predicted body fat and "mean" body weight. Measures of body weight are needed, however, when the animal is in a normal unstressed environment. His findings supported the use of D20 to predict other components of body composition as well. Arnold et al. (1985) evaluated the one compartment model, (1P). He found that empty body o\° protein (EBP) was overestimated by 3.6 and gastrointestinal tract. water (GITHZO) was also overestimated by 13.4% with this method. Further improvements are necessary to develop consistently accurate equations. Shipley and Clark (1972), after examining body water tracer kinetics, proposed numerous predictive equations which utilize dilution principles. In an effort to solve the problem of overestimation of body water due to variable 31 gut water, Byers (1979b) proposed separating body water and GITHZO into two pools. As pointed out by Smith and Sykes (1974), the majority of the variation in fat content can be accounted for by variations in empty body weight and water content either with or without GITH2O included. Theoretically then, accurate elimination of gut water by a dilution curve peeling process should improve prediction equations which can assess body composition. Byers (1979b) applied his system to a diverse group of cattle ranging from calves to cows. D20 dilution predictions were shown to be correlated with actual chemical analysis (r2=.965) and specific gravity (r2=.952). McCarthy (1983b) used the same procedure comparing small and large frame steers. He found high correlations for DS derived values with 9-10-11 rib section analysis, but low relationships between DS values and specific gravity, and between specific gravity and 9-10—11 rib section for water and fat. Ferrell and Jenkins (1984) applied the D20 space technique to mature cows. They found that the relationship between D20 pool size A (empty body water space) and the weight of body fat to be low (r2=.08). Modifications of the regression analysis to include EBW greatly improved the relationship (r2=.86) to estimate body fat. Empty body weight was highly predictable from live weight and D20 pool B (GITHZO). However, due to high residual standard deviations in estimating weight of body fat, they found the 32 usefulness of D20 space to be limited. Martin and Ehle (1986) reported body composition changes in dairy animals during and between lactations and ages large enough to merit further work and refinement. This observation also supports work by Odwongo et al. (1984) in dairy cattle. Lunt et al. (1985b) used D20 space to predict carcass composition in 32 Brahman, Angus and Brahman x Angus steers slaughtered after various gains in live weight. They found USDA yield grade (YG), specific gravity (SG), 9-10-11 rib section (RIB) analysis and chemical composition to more accurately predict carcass composition than D20 dilution. This should be expected, since YG, SG and RIB evaluate only a portion (carcass) of the total body components. D20 dilution, on the other hand, predicts the composition of the entire animal (carcass, hide, head, and viscera) of which a substantial amount of body fat and protein may be associated with noncarcass components. Miller et al. (1988) used 50 cattle ranging in age from calves to cows and found results similar to those of Lunt et al. (1985b). Arnold et al. (1983,1985) compared body composition as estimated by the one pool (1CM) system of Loy (1983), the two pool (2CM) model (Byers,1979b) and a three comparment (3CM) model which consisted of intracellular, extracellular and GITHZO components for the direct measurement of body composition in 30 steers. They indicated each method has shortcomings for estimating body composition. The 1CM 33 method appears to more accurately estimate empty body ether extract (r=.82) than the 2CM method (r=.59). The 2CM method, however, more accurately predicted total body water, r2=.90 vs .84. The 3CM method showed no improvements over the 2CM method in estimatimg body water. Byers (1986) used 50 cattle ranging from calves to mature cows to assess the applicability of the 020 dilution technique and other procedures to estimate body composition in beef cattle. In addition to standard curve peeling techniques, a Simplified biexponential regression procedure was presented. Predictions of EBW, GITHZO and fill were all highly correlated (r2=.97,.86,.90, respectively). Empty body weight, water, protein and lean body mass were also highly predicted, r2=.98 +/— about 2% for EBW and 7% for the other lean body components. As expected, fat was more ‘variabler‘when jpredicted (r2=.88, CV=24.6%) but inclusion of ultrasonic measurements reduced variation and increased precision. The literature contains numerous conflicting comparisons which suggest the need for further studies and refinement of these procedures to increase the precision of their predictive value. Further studies evaluating these techniques which measure body and carcass composition using cattle differing in sex, age, fatness, muscling, breed and diet are needed to establish well proven and accepted techniques for use by scientists interested in 34 body composition, particularly with todays leaner, later maturing animals. Methods of Estimating Carcass Composition Whole ib Composition. Hall and Emmett (1912) and Moulton et al. (1922) reported close relationships between wholesale rib composition and that of the beef carcass after dissection. Lush (1926) and Hopper (1944) reanalyzed the same data on 92 cattle and agreed with Trowbridge (1918) and Moulton (1922) that composition of wholesale ribs was representative of the entire carcass. Hopper (1944) presented prediction equations comparing muscle, fat and bone components as well as chemical composition of the wholesale rib to that of the carcass. The rib was selected for its ease of removal and higher correlation to carcass composition compared to other cuts. Berg and Butterfield (1976) and Moran (1982,1983) pointed out, however, that due to genotypic differences among animals and different management systems, proportions of carcass muscle and fat in different cuts may lead to erroneous conclusions. Further refinements of the wholesale rib section analysis have decreased costs and economic loss through the use of portions of the rib. 9-10-11 Eip Section. The work of Hopper (1944) stimulated research on the wholesale rib, or parts of the rib (Hankins and Howe, 1946) to determine the relationship 35 of the 9-10-—1l rib to that of the entire rib and dressed carcass. In their studies, the 9-10-11 rib sections from 197 cattle were separated into muscle, fat and bone. Chemical analysis was performed on these tissues. High correlations between separable fat and lean, along with chemical fat and protein, with both the wholesale rib and the carcass were found. Hankins and Howe provided detailed procedures for separating the 9-10-11 rib section to improve consistency between investigators. This method has routinely been followed, supplying relatively accurate results in most serial slaughter trials and reduced expense compared to the wholesale rib. This method, however, has several drawbacks which many researchers ignore (Moran, 1982). Among the problems with this procedure is the decreased ability to accurately predict the amount of lean in the carcasses of heifers. The major concern originates from the fact that these equations have been developed from animals of a specific species (Bos taurus) produced under a specific management system which can influence composition. Moran (1982, 1983) and Berg and Butterfield (1976) point out these variables can lead to less accurate predictive ability. Since the publication of the equations by Hawkins and Howe, numerous investigators have successfully applied them or developed similar equations which use the separable and chemical components of the 9- 10-11 rib from animals of different breeding or management 36 systems (Jones, 1982,1985c: Lunt et al., 1985b: Miller et al., 1988). These researchers evaluated several commonly used. methods of estimating carcass composition and consistently report the 9-10-11 rib to be the method of choice with the highest correlations. Alhassan et al. (1975) used the 9-10-11 rib section and carcass weight to predict empty body composition. These researchers concluded that prediction of body water and ash from weights of 9-10-11 rib moisture, ash and carcass weight were unacceptable. They also noted a difference in maturity between the Angus and Hereford steers used in the experiment. Their findings suggest that the rib section was more acceptable in predicting body composition across breeds than body weight measurements. 10th and 12th Rib Sections. Limited information is available on the use of the 10th and 12th rib section separable components to predict carcass composition. Crown and Damon (1960) found correlations of .96, .82 and .75 for percentage separable fat, lean and bone, respectively, of the 12th rib and corresponding carcass components. On the other hand, Ledger and Hutchison, (1962), found low relationships between separable and carcass components. Due to descrepancies in findings this procedure has not received much attention. 37 6-7-8t pip Section. Several researchers (Alexander, 1961; Meyer, 1962: Hedrick et al., 1963) related the separable components of the 6-7-8th rib section to the yield of trimmed wholesale cuts. While the correlation coefficients were significant ( r2 >.6) for muscle and (r2 > —.6) for fat, they are lower than those reported by Hankins and Howe (1946) for the 9-10-11 rib section. Rib Core Section. Kennick and England (1960) explored the use of a smaller rib section to determine carcass composition. They used a core sample from between the 8- 9th and 9-10th rib to relate to carcass composition. They suggested this method could be useful with large number of animals, but it has never gained support. Wholesale Flank. Separable components of the flank were reported by Hankins and Howe (1946), Hedrick et al. (1963), Knapp (1964), Miller et al. (1965), and Allen et al. (1966) to be highly related to total carcass muscle and fat. Hankins and Howe (1946) actually found the correlation between flank separable fat and percentage ether extract to be higher than the 9-10-11 rib section, (.95 vs .93). Hedrick et al. (1963) reported the percentage fat in the wholesale flank was significantly correlated with percentage trimmed wholesale cuts (r=-.86) and trimmed primal wholesale cuts (r=-.80). Additionally, Miller et al. (1965) indicated percentage retail yield of 38 the flank was highly related to percentage boneless retail cuts (r=.78) and partially boneless retail cuts (r=.81) of the carcass. Knapp’s (1964) findings were in agreement with these observations for the flank (r=.75). Allen et al. (1966) compared 'various carcass cuts including' the flank from carcasses of several weight and fat thickness groups. Correlations between separable muscle, fat and bone in the flank and the carcass were .91, .91 and .32, respectively. These reports consistently showed higher relationships for the flank than the round. Thus, components of the flank have been shown to be highly correlated to muscle and fat in the entire carcass. Since the flank is one of the less valuable cuts in the carcass, the monetary loss from each carcass makes this an attractive :method. of jpredicting’ carcass. composition. However, use of this method is limited by potential differences in technique of flank removal and the possibility of excessive errors. We 893131; High correlations between separable muscles in the round and the yield of the carcass have been reported. Cole et al. (1960b) indicated that muscles in the round account for 90% of the variation in total carcass muscle. Miller et al. (1965) and Cahill (1966) showed significant relationships ( r>=.80) between the round (trimmed and boneless) and partially boneless cuts of the carcass, primal cuts or weight of retail cuts (Tuma et al., 1.! 39 .1967). 1.1.5.811; Sm W Use of meat tissue sawdust has been examined by several researchers to evaluate its value for prediction of carcass composition. Vance at al. (1970) reported significant correlations (P < .01) between chemical components of beef carcass sides and meat sawdust obtained by sawing through the round, loin, rib and chuck of frozen sides at 2.54 cm sections. Williams et al. (1974) used Vance’s technique in three trials with bull carcasses averaging 282 kg: Holstein calves averaging 138 kg and frozen carcasses from Holstein bull calves which averaged 338 kg live weight. They found that frozen carcasses, as compared to chilled carcasses, yielded the most reliable results when sawed at 2.54 cm intervals. Correlations between sawdust composition and carcass chemical composition ranged from .72 to .94 for carcass moisture and fat. Correlations of carcass protein and carcass ash with sawdust composition ranged from .64 to .68. Sawdust from chilled sides was considerably less reliable than sawdust from frozen sides as a predictor of carcass chemical composition, thus limiting the application of this technique, since the majority of beef carcasses are merchandised in the fresh chilled state. Specific Gram Application of the carcass density principles to live subjects and tissues has been popular 40 over the past 50 years. Studies with humans by Behnke et al. (1942), as well as by Keys and Brozek (1953), were successful in measuring body fatness. As pointed out by Pearson et al. (1965, 1968) however, application of this procedure is virtually impossible with live animals. Therefore, use of specific gravity has generally been limited to postmortem components in animal studies. Conceptually, specific gravity separates the carcass into two pools. The lean tissue has a density of 1.10 and fat is about .90. By weighing the carcass or cut in air and then in water, the density of the entire carcass can be determined. Numerous considerations must be taken into account, in developing equations, as outlined by Garrett (1968) and reviewed by Pearson et al. (1968) and more recently by Jones et al. (1978a). Briefly, the temperature of the water and the carcass, degree of hydration or dehydration of the carcass and the amount of trapped air in the carcass or cuts influence specific gravity. In studies by Pace and Rathbun (1945) with guinea pigs, and Kraybill et al. (1953) with pork, Kirton and Barton (1958) along with Field et al. (1963) with lambs, demonstrated the usefulness of specific gravity as an index for measuring fat. Studies by Kraybill et al. (1952), Garrett et al. (1959), Kelly et al. (1968), Garrett and Hinman (1969), Preston et al., (1973), Ferrell et al., (1976) and Jones and Rompala (1985a) have provided high 41 correlations between specific gravity (density) and fat in beef’ carcasses. Additional studies have also been conducted with the use of specific gravity on certain carcass cuts and(or) muscles to assess carcass composition (Hopper, 1944: Lofgreen and Garrett, 1954; Orme et al., 1958; Cole, 1960a: Field et al., 1963: Latham et al., 1966; Ledger et al., 1973; Mata-Hernandez et al., 1981). Hedrick (1983) pointed out that studies by Waldman et al. (1969) and Gil et al. (1970) determined that specific gravity is not accurate for carcasses with low amounts of fat (< 20%). Garrett et al. (1968) and Riley (1969) indicated that the equations using specific gravity as an index of composition are likely to be more accurate with fatter carcasses since higher proportions of fat have lower specific gravity values. These reports are supported by the work of Preston et al. (1974) and Fortin et al. (1980a:1981) which indicate that; measurement. of specific gravity for individual carcasses is highly variable, but if compared between groups of carcasses, relatively large differences in composition can be detected. Recent studies by Kempster et al. (1982a) and Jones et al. (1985a) using simple carcass measurements (e.g., fat thickness measurments) in conjunction with specific gravity provide a better prediction of carcass lean. Powell and Huffman (1968) found specific gravity results similar to those found by Kraybill, Bitter and Hankins (1952) and - - , 42 Garrett and Hinman (1969). On the other hand, Lunt et al. (1985b) using Brahman, Angus and Brahman x Angus crossbred steers, found specific gravity accounted for a suprisingly low amount of variation (63 to 80%) in the percentages of separable lean, fat and bone in carcasses varying widely in composition. Miller et a1. (1988), using a group of cattle from diverse biological types and mature sizes, concluded that specific gravity was not a useful tool for predicting composition in any age class from calves to cows. Miller cited problems caused by hide pullers, which entraps extra air between the fat and muscle, as one of the major reasons for unexplained differences in hindquarter and forequarter weights in water. This resulted in the inability of specific gravity to adequately estimate carcass composition in their study. It should be pointed out, that in early studies, as well as in studies today that attempts to use specific. gravity' as 21 tool to measure composition, carcasses should be dressed using the cradle methods. This prevents entrapment of excessive air under the fat. Also, past studies have repeatedly shown poorer predictive values in carcasses with less than 20% chemical carcass fat. These considerations should. be taken into account when designing studies or interpreting results. Relationships pf_Marbling Score pg Carcass Comppsition, Ether Extractable Lipid Content p: other Major Muscles and _____ ____ ______,_ ___ _________________-illlllllll 43 Changes i_1_1_ Muscle E 139112 Ratios. Intramuscular or intrafascicular adipose tissue (IFAT) commonly called marbling, has been examined by several researchers observing developmental increases in IFAT and its affects on muscle:bone ratios. Others have evaluated the usefulness of marbling score (Brackebush et al., 1988: Savell et al., 1986) and(or) content (Kauffman et al., 1975), in predicting carcass composition and ether extractable lipid (EEL) or fat of the longissimus dorsi (LD) and other muscles. Johnson et al. (1972) conducted a feeding study in which. about. 10 percent. of 'total fat was found in the intramuscular adipose tissue site. ‘Fhis relationship appeared to be constant when total side fat was about 16 kg. Whether 10 percent of total fat in IFAT is a general figure for most cattle remains unanswered, but Berg and Butterfield (1976) indicated. there is an indication of genetic differences in quantities of IFAT and subsequent differences in the EEL found in IFAT. Berg and Butterfield (1976) also cited studies by Damon et al. (1960) and Kauffman et al. (1968) which relate increases in subjective marbling score to increases in fat thickness. This has generally become accepted as dogma in the beef industry. Still others have examined the effect of IFAT development on muscle:bone ratio. Berg and Butterfield (1976), after reviewing several studies, observed that in 44 cattle with a muscle:bone ratio of 4:1 at 110 kg muscle plus bone weight, IFAT contributes .27 to the muscle in the ratio of 4:1. In the same cattle with 40 kg muscle plus bone weight and a muscle:bone ratio of 3.80:1, .14 of the muscle in the ratio was contributed by IFAT. They summarized their findings by suggesting a large part of the changes in muscle:bone ratio associated with increased weights could be explained by changes in fat within the muscles. Cross et al. (1975) examined variations in marbling content in different muscles of beef carcasses. They compared the differences between marbling score required to quality' grading ‘the (entire carcass versus the marbling score needed to quality grade individual carcass wholesale cuts. These researchers found lower marbling scores in the cross section of the round/loin and chuck/rib interfaces than the 12-13th rib interface. Also, as marbling content in the 12-13th rib decreased, marbling scores in the round and chuck also decreased in almost all cases. These findings contrast with those of Cook et al. ( 1964) who found an increase in marbling from the 12th to 6th thoracic vertebra. Doty and Pierce (1961) also reported variations in marbling scores and chemical fat content in the longissimus muscle from the 11-12th rib to the 7th/8th rib cross section. v.‘ 45 Kauffman et al. (1975) suggested marbling score be used not only as an index for quality, but, in conjunction with U.S.D.A. yield grade, as a quantitative measure to predict fat - free muscle in beef carcasses. They developed regression equations using numerous carcass traits including marbling score to estimate percent fat standardized muscle. Brackebush et al. (1988) found the fat content of all muscles in their study to be linearly related to LD fat content. The R2 values ranged from a low of .81 for the supraspinatus, to a high of .92 for the spinalis dorsi. They concluded that percentage fat (EEL) in the LD can be used to predict the composition of other major muscles of the beef carcass. Savell et al. (1986), responding to consumer concerns about fat content in beef, collected longissimus samples from the 13th rib of 518 beef carcasses ranging in marbling score from moderately abundant to practically devoid. They determined EEL and moisture content which ranged from 10.42 and 68.14 percent, respectively, for moderately abundant, to 1.77 and 75.37 percent, respectively, for practically devoid marbling scores. They developed a regression equation which predicts the percentage EEL of the longissimus at the different marbling scores. The equation: 46 O 6 EEL =(marbling score x .0127) — .8043, (R2 =.779), appears to adequately estimate EEL of the longissimus with external adipose tissue and epimysium removed. Relationships 9: Individual Muscles g_ Grou s p; Muscles pp Carcass Composition apg Carcass Lean. As previously mentioned, several researchers have reported that either entire wholesale cuts or parts of wholesale cuts can be used to estimate carcass composition, usually with high predictability, particularly for carcass muscle in hogs (Lush, 1926; Hammond, 1932; McMeekan, 1941) and beef (Hankins and Howe, 1946; Hankins et al., 1959; Crown and Damon, 1960; Cole, 1960a: Butterfield, 1962; Callow, 1962). Numerous muscles or groups of muscles have been excised to examine relationships between muscle weight and total separable carcass lean. Orme et al. (1960) dissected carcasses of mature Hereford cows, removing the longissimus dorsi (LD), semimembranosus and adductor (SM and AD), semitendinosus (ST), biceps femoris (BF), quadriceps (Q), psoas major (PM), triceps brachii (TB), and infraspinatus (INS). They found significant relationships, to varying degrees, between muscle weights and total carcass lean. Butterfield (1962) used the same muscles and the shin group from purebred Hereford or Brahman and Hereford )< Brahman cattle to predict total muscle. He observed even higher correlations than did Orme et al. 47 (1960). Butterfield (1962) also indicated little effect of genetics on the relationship of muscles or groups of muscles to total muscle. He stated further that the influence of age on muscle content appears to be insignificant after six 'months of age. Price and Berg (1977) also used a group of muscles similar to Butterfield (1962) to predict total carcass muscle, stating that the relationship between predictor muscles and total muscle of the side can give meaningful estimates of total muscle of the side in a wide range of carcass types. Recent work by Lunt et al. (1985a) with Angus, Brahman and crosses of these breeds, showed high relationships between certain muscles and(or) groups of muscles with total carcass lean. Their study, however, disagrees with earlier findings of Orme et al. (1960) and Butterfield (1963), exhibiting high variations between breeds when using muscles to predict total carcass lean. Relationship 9: Longissimus Eggs; Apea pg Predict Tppgl Muscle. Measurement of the cross section of the longissimus dorsi (LD) muscle at the 12th rib interface has received some interest over the past 50 years as an estimate of carcass muscle mass. Mackintosh (1937) used a sheet of parchment paper to trace an outline of the muscle and then measured area with a pflanimeter. Stull (1953), Schoonover and Stratton (1957) and Shrewsbury and Wideman 3. x :3 48 (1961) described techniques to measure the LD by photographing the muscle and then using either a wire grid or a planimeter to obtain the area. Henderson et al. (1966a) were among the first to refine the present plastic grid system for measurement. While not as precise as a planimeter, the differences were small. Ribbing differences between sides or carcasses are responsible for the majority of cross sectional area discrepancies (Hedrick et al. (1965). Several researchers (Cole et al., 1960: Goll et al., 1961: Cole et al., 1962; Abraham et al., 1968) related the LD area to the separable lean in the carcass. They found the LD area to be associated with only about 18% or less of the variation in total carcass lean. Theoretically, use of LD area to predict muscle is sound, since the impetus for growth of this muscle, described by Berg and Butterfield (1976), is average. Unfortunately, numerous environmental and genetic variables exist which limit the usefulness of this measurement as a reliable predictor of total muscle in beef carcasses. Prediction 9f @912! _dey egg Carcass Comppsition by Linear apg Multiple Regpession. Hopper (1944) and Hankins and Howe (1946) were among the first to develop linear regression equations for predicting beef carcass composition from the physical and chemical components of the wholesale rib and the 9-10-11 rib section. It is 49 beyond the scope of this dissertation to review all methods. Hedrick (1983), however, reviewed the literature citing a vast number of studies in which equations are available to predict body and carcass composition. The major problem. a researcher encounters when developing prediction equations includes identification of the "best" equation (MacNeil, 1983). At best, the definition of "best" could be considered nebulous. A commonly cited definition is (MacNeil,1983): a) the equation must be unbiased or without discernible trends in the errors of the prediction, and: b) the accumulated squared errors of prediction should be maximized. Interpretation of results using prediction equations to estimate composition should be a major concern of scientists. working in studies which. measure changes in animal composition by prediction equations. Correlation coefficients (r) and coefficients of determination (r2) have traditionally been the major index referred to determining usefulness of equations. r2, sum of squares due to regression (SSr) corrected total sum of squares (SSY) is usually maximized which provides a convenient statistic identifying the models (equations) having the largest sum 50 of squares due to regression within that study. Maximum r2 is commonly interpreted to mean that the equation with the highest r2 accounts for the greatest percentage of total variation in Y (the dependent variable) of all equations. MacNeil (1983) demonstrated that an equation with a maximum r2 can in fact, have prediction error variance larger than the other equations derived from the same data. In determining the correlation coefficient (r) between the assumed random variables X and Y} 1: is influenced by the range of values in the sample on which it is based. Correlation coefficients derived from biologically diverse populations will be considerably higher than those from a less variable population and potentially lead to erroneous conclusions. Cross (1982) provides a: classic: example of misinterpretation of correlation coefficients derived from data between two groups of animals, which is presented in Table 1. The r2 for group I is much higher than group II, suggesting the predicting equation from group I is more accurate. However, considerably legs variation exists in group II carcass lean percentage resulting in a low r2 value. Prediction of carcass lean percentage in group II would have no more error than group I, since the residual standard deviations (RSD) are equal“ Cross suggests that since RSD accounts for the variation in Y, this would be a better equation selection criterion. Ideally, an equation 51 having a high r2, as well as a low RSD, would be preferred. TABLE 1. Comparison of Predictive Accuracy Between Two Groups of Pigs Trait Group I Group II Backfat thickness, cm (X), standard deviation 5.1 2.99 Percentage lean, % (Y), standard deviation 4.1 2.29 R2 .75 .21 Residual s. d., % 2.05 2.05 MacNeil (1983) and Moran (1983) discussed the evaluation, selection and use of prediction equations for various scientific objectives. .Accuracy should be the ultimate concern when selecting an equation and precision should only be a secondary factor in choosing the final equation. The ultimate test of a prediction equation’s usefulness for future experiments is the validation of the equation in several independent samples. Successful validation requires measurement of the trait to be predicted (Y) and the predictors (X’s), in the independent samples, just as in the original population from which the equation is generated. Validation over a wide range of conditions (including different genotypes, management procedures and environments) is critical to prevent bias. The regression 52 of predicted Y on the observed Y should have an intercept not significantly different from zero and a slope not significantly different from one. Failure to meet these criteria, indicates that the prediction equation could be biased (Gill et al, 1978). The utility of a prediction equation can be compared to an untested hypothesis until it is validated with independent. data sets. ZPreviously' published. prediction equations should be applied to new data sets generated by researchers collecting composition data and then publish the results. MacNeil (1983) states: "results should be published regardless whether they support validation or discourage future use of the equation. Until the prediction equations are validated on animals other than those from which the original equation was formulated, their utility remains questionable." Chapter 1 Changes in Empty Body, Carcass Composition and Relationships between Moisture, Fat and Protein of Major Tissues in Large Framed Beef Steers at Four Different Weights 53 ‘0. ..., ‘9'." ABSTRACT Developmental changes in empty body, carcass composition and composition of gain was determined on 20 continental European crossbred steers representing four slaughter groups. Five steers were slaughtered at each weight group (G1:300: 62:390: G3:480 and G4:560 kg live weight). Average number of days on feed between slaughter groups was 64, 64 and 55. Complete physical dissection and chemical composition of all individual empty body (EB) and carcass tissues were conducted on each steer. EB weight as a percentage of live weight was 91.8, 91.9, 91.7 and 92.7% for Gl to G4, respectively. Percentage EB moisture (EBHZO) and protein (EBP) decreased from 60.9:19.0 in Gl to 52.3:16.5% in G1 to G4, respectively. Percentage EB fat (EBFAT) increased from 15.1 to 27.1% in Gl to G4, respectively. Carcass moisture and protein decreased from 63.9:18.11 in 61 to 52.64:14.51% in G4, respectively. Carcass fat increased from 16.87 in 61 to 32.01% in G4, respectively. Skeletal muscle as a percentage of live weight and EB weight decreased (P<.05) from 42.3:46.09 in G1 to 38.7:41.75% in G4, respectively. Carcass skeletal muscle decreased (P<.05) from 66.0 to 57.9% from 61 to G4, respectively. The ratio EBH20:1ean body mass (LBM) did not differ (P.10) between groups averaging .72. The ratio 54 55 EBHzozEBP (3.2) did not differ (P>.10) between slaughter groups. EB fat gain (g/d) was 537.0 from d 0 to 183. EBP gain (g/d) was 178.7 from d 0 to 183. Carcass fat and protein gain (g/d) was 417;100.1, respectively, during the 183 d feeding period. EB skeletal muscle accretion (g/d) was 484.7 from d 0 to 183. Hide and the gastrointestinal tract as a percentage of EB weight did not differ (P>.10) between groups. The greatest change in composition of dissectible tissues occurred in the EB and carcass nonskeletal. muscle soft ‘tissues (mainly' adipose 'tissue) which increased from 15.4 to 24.4% of EB weight. INTRODUCTION The early studies in beef composition conducted by Trowbridge (1919): Haecker (1920): Moulton (1922b): Hopper (1944): Hankins and Howe (1946); Callow (1961, 1962); Luitingh (1962) and Johnson et al. (1972), examined the composition of British bred beef cattle typically 18 to 24 months of age or older. Numerous relationships and growth patterns of empty body components have been derived from these studies. During the past 15 to 20 years however, there has been an increased interest in continental European breeds of cattle for use in crossbreeding programs with British breeds. One of the main objectives in cross breeding has been to increase the muscle content in the carcasses. During the same period, the trend in beef production has moved toward marketing at younger ages. Some researchers (Cole et al., 1964: Brungardt, 1972: Berg and Butterfield, 1976 and Koch and Dikeman, 1977) have demonstrated that continental European breeds and their crosses have faster growth rates and heavier mature weights than British breeds. With increased use of continental European genetics in crossbreeding and selection for larger framed British breeds, more information is needed examining the effect of 56 57 faster growth rates, younger slaughter ages and heavier mature weights on the distribution and relationships between major body tissues and empty body moisture, fat and protein. Since empty body and carcass composition have been and are an increasingly important basis for treatment comparisons, this study was designed to examine the growth, development and distribution of major empty body tissues of continental European crossbred steers typical in today’s feedlots. A second objective of this study was to gather data and relationships between moisture, fat, protein and mineral content on leaner, later maturing cattle which can be used to update and develop equations which more accurately predict the composition of today’s leaner, heavier weight cattle. MATERIALS AND METHODS Experimeppal Animals, Twenty Simmental X Charolais X Angus steer calves were selected from one producer’s calf crop of 350 genetically similar steer calves. The calves were selected specifically to represent the large frame size described in the official U.S. feeder cattle grade standards (USDA,1979) and muscle thickness designation No. 1, described by USDA (1976). Calves were selected on body condition score, weight, projected optimal final market fatness and projected market weight. Initial body weights of all animals was 260 kg (+/- 10 kg). Steers were housed unrestrained and exposed to ambient temperatures and photoperiods from January to September. Animal Expupipgy Animals were randomly allotted five per slaughter group to four groups. Group 1 (Cl) steers were slaughtered when each steer weighed approximately 300 kg, 62 approximately 390 kg, G3 at 480 kg and G4 at 570 kg, fasted live weight. Steers were fed a typical complete feedlot grower diet (Schroeder, 1987: 13%CP, 1.88 Mcal NEm/kg: 1.22 Mcal NEg/kg) until all animals from GZ were slaughtered. At that time, the remaining steers were switched to a typical feedlot finishing diet (Schroeder, 1987: 11%CP, 1.98 Mcal NEm/kg: 1.3 Mcal NEg/kg) until the steers reached the designated slaughter endpoint. Average 58 59 days on feed between slaughter groups was 64, 64 and 55, respectively. Each steer was weighed every two weeks after feed had been withheld for 16 h. When steers approached the designated slaughter weight, each steer was weighed every 7 d after feed had been withheld for 16 h prior to weighing, until the slaughter date was determined. Immediately prior to slaughter, feed was again withheld for 16 h and each steer was weighed. Water was supplied ad libitum at all times. Animals were transported to the meat laboratory, immediately reweighed and hip height measurements taken. One steer was slaughtered each day according to common commercial procedures. Tissue Collection, Eissection apg Determination pf _Eppty m and Carcass Composition. At slaughter, all tissues (including blood) were collected as quickly as possible, weighed (to nearest gram) and subsampled. Blood was subsampled as bleeding occurred in heparinized containers to facilitate accurate determination of blood composition. Tissues requiring further dissection were placed in moisture impermeable bags to prevent water loss. Tissue samples were either immediately frozen in dry ice in their entirety or ground, subsampled and placed in a -400 C freezer for later analysis of moisture (M), ether extractable lipid (EEL) and protein (P: N x 6.25) content (AOAC, 1980). A complete list of abbreviations for dissected empty body components, carcass tissues, muscles 60 and bones _is found in Appendix Tables 1, 2 and 3. Upon removal of the intact hide, the hide was cleaned of any remaining subcutaneous adipose tissue (ScAT) and muscle. The hide was immediately weighed (to nearest .05 kg), split medially and one half sampled in ten different locations and ground for analysis. One front foot and one hind foot was removed weighed and dissected into bone and soft tissues. The tail was removed, ScAT removed, weighed, ground and later analyzed. The head (minus the tongue) had the brain removed, the remainder split into right and left sides and all soft tissue removed from the right side. Immediately after removal of the hide, proportionate ScAT subsamples were removed from. twelve different locations from the right side of the carcass. All remaining ScAT was rapidly removed from the right side of the carcass to minimize moisture loss. The ScAT was ground three times (3 mm plate) and subsampled. The gastrointestinal tract (GIT) was removed, weighed and emptied of contents. All GIT individual components listed in Appendix Table 3, were separated, re-weighed and later analyzed. All Iother’ abdominal. and. thoracic cavity noncarcass components were removed, separated, weighed and stored for later analysis. Prior to splitting the carcass, the right and left kidneys were removed. and weighed individually. Additionally; the right. side kidney' and. pelvic adipose 61 tissue (KP) was removed, weighed and frozen for later analysis. Care was taken in splitting the carcass to ensure minimal deviation from the medial plane of the vertebra. Any deviations were immediately corrected while splitting. Any unevenly split bone was removed from the corresponding side and added to the opposite side. Hot carcass weights from the right side were corrected to include all previously mentioned fat depot subsamples. The left side was weighed, shrouded and chilled for 24 h. Fat thickness measurements, (to the nearest mm), longissimus dorsi (LD) cross sectional area (REA) were determined and percentage KP fat estimated. USDA (1976) yield and quality grade data were obtained by trained university personnel. After splitting and completion of right side ScAT removal, intermuscular adipose tissue (IMAT) subsamples were removed from the round, loin, rib, chuck, plate and brisket, (between the major groups of muscles), pooled and analyzed. Eight individual muscles listed in Appendix Table 2, were quickly removed individually, dissected, cleaned of all external adipose tissue and weighed. Muscles were subsampled and analyzed for M, EEL and P. Twenty five muscles of the right side, listed in Appendix Table 2, were subsampled (proportionate to weight) and composited. The composited muscle sample was ground, powdered and analyzed 62 to determine the amount of intramuscular EEL in the carcass. Intramuscular adipose tissue (IFAT: 3 to 5 g) was dissected from a second subsample of the same twenty five muscles to determine M, EEL and P content of the IFAT, for later calculations of composition. Rapid dissection of the remaining skeletal muscle, adipose tissue, heavy connective tissues plus tendons and bone plus cartilage was completed. Bones were dissected completely free of muscle, fat, tendons and ligaments, but not cartilage, and separated either into individual bones or groups of bones for later analyses. Individual and group bone weights taken included: femur, tibia/fibula, radius/ulna, humerus, 3rd and 10th rib, skull, vertebral column, lower leg (front and hind foot), hind limb (carcass), front limb (carcass) and rib cage (including sternum and costal cartilages). All bones were ground by groups using an Autio 801 whole body grinder at The Ohio State University, Columbus, OH. After grinding, 10% of the weight of each group was taken for analyses. All groups of bones from the carcass were combined for a composite sample and 10% of the total weight subsampled. In order to correct for removed bone subsamples, an extra 10% of noncarcass bone groups was removed before pooling all ground bone to arrive at the composite total body bone to be subsampled for analyses. 63 Determination p; Skeletal Muscle, Marbling an Intermuscular‘ Adipose Tissue fronl Right Sides and Total Body. All soft tissues (less Sc fat, tendons and ligaments) dissected from the right side (including the head) were weighed, ground 3 times (3mm plate) and subsampled. Appendix Table 4 contains a complete list of all abbreviations which follow for use in calculating fat- free muscle, skeletal muscle, etc. Percentage moisture (M), ether extractable lipid (EEL) and protein (P: N X 6.25) in the intermuscular and intramuscular AT (EELIMIF) and other soft tissues from the right side of the carcass were determined (AOAC, 1980). From this sample, the EELIMIF represented the lipid from the intermuscular (IMAT) and intramuscular (IFAT) adipose tissue. The remainder of the sample is referred to as the fat—free muscle (FFM). The FFM includes the moisture and protein associated with the muscle along with the IMAT and IFAT. The quantitative estimation of the weight of the empty body muscle, IMAT and IFAT can be determined using the following calculations which are diagrammed in Appendix Table 5. The weight of FFM was divided by the difference of one minus the percentage EEL in the composite muscle sample taken from the previously mentioned 25 muscles of the right side (1- %EEL of composite muscle marbling determination sample). This resulted in the weight of the skeletal muscle, as well as marbling adipose tissue (includes 64 M,EEL,P) and the M and P associated with the IMAT, labeled FFMEE. The difference between FFMEE and FFM represents the EEL from the IFAT of the skeletal muscle (EEIFAT). The EEIF is subtracted from the EEIMIF which resulted in the EEL associated with the IMAT (EEIM). The EEIM is divided by the percentage EE of the IMAT sample which gives the total weight of the IMAT. To determine the M and P associated with the IMAT, the EEIM is subtracted from the IMAT giving the moisture and protein (MPIM) associated with the IMAT. In order to determine the estimated muscle tissue, M and P associated with the IFAT, the MPIM is subtracted from the FFM giving the total estimated fat-free muscle and marbling adipose tissue M and P, (FFMIF). Adding the EEIFAT to the FFMMA gives the estimated total skeletal muscle and marbling adipose tissue (TMM). The total weight of the marbling adipose tissue (TIFAT) is derived by multiplying the TMM by the percentage of total marbling adipose tissue (T%IFAT). Determination of T%IFAT is accomplished by dividing the percentage of EEL in the composite muscle sample (represents IFAT EEL) by the percentage EEL of the dissected composite marbling sample. Skeletal muscle tissue without IFAT, (TM) can then be derived by subtracting the TIFAT from the TMM. Conversion of the right side tissue weights (muscle, subcutaneous AT, intramuscular AT, intermuscular AT and bone) to total body tissue weights was performed since 65 earlier studies by Butterfield (1963), Briedenstein et al., (1964) and Hedrick et al., (1965) have shown that cattle and pigs to exhibit bilateral symmetry. The tail, kidneys, perirenal fat and any internal cavity tissues which do not exhibit bilateral symmetry were removed prior to converting all right side tissue weights, to left side tissue weights and then to total body tissue weights. The weights of all tissues (muscle, adipose tissue and bone, etc.) as a percentage of the right side were multiplied by the weight of the left side to give the weight of the tissues in the left side. Weights of tissues from both sides were summed to determine the total weight of muscle, adipose tissue (all depots), bones and other tissues in the body. After completion of all individual tissue analyses, the weights and respective composition of major empty body organs and tissue groups listed in Appendix Table 1 were recombined to determine actual empty body (EB) composition in kilograms and percentage of the respective tissue groups, as well as kilograms and percentage EB water (EBHZO), EB fat (EBFAT) and EB protein (EBP). Additionally, all carcass tissue weights and composition, also listed in Appendix Table 1, was recombined to determine actual kilograms and percentages of carcass water (CARCHZO), carcass fat (CARCFAT) and carcass protein (CP). Empty body and carcass ash, EBASH and CARCASH, respectively; were: determined. as the difference of all 66 other EB and CARC components from 100%. The summation of all tissue weights was at least 98.5% of initial EB and carcass weight. Statistical analysis. Group means and standard errors for weights and percentages of EB and carcass, respectively, and analysis of variance were performed according to SPSS Base Manual (Statistical Package for the Social Sciences, 1989). RESULTS AND DISCUSSION Liye Performance apg Carcass papa; Means and standard errors for the various carcass traits are presented in Tables 1-1 and 1-2. All steers were started on feed at the same time and fed until each steer reached the designated fasted slaughter weight, 1J1 each randomly assigned group. The average live weight of the initial slaughter group (G1) was 298.5 kg and increased by approximately 90 kg between G1 and group 2 (G2), and between 62 and group 3 (G3) but only 75.54 kg between G3 and group 4 (G4). This descrepancy was due partly to the difficulty in estimating amount of fill in the gastrointestinal tract (GI) and the increased weight loss associated with handling during transportation to the meat laboratory. As indicated in Table 1-1, the percentage empty body weight of the live weight was the same in G1, G2 and G3, while in G4 the empty body weight was 92.7% of the fasted live weight suggesting there was indeed more shrink in G4 steers between the time the steers were weighed at the research unit and the final weighing immediately before slaughter the next morning. The average final slaughter weight of 555.5 kg did not present any adverse effect on the final experimental outcome and carcass dissection, since all animals in G4 had attained the desired endpoint 67 68 of USDA quality grade of low Choice, fat thickness of at least 10 mm and yield grade of 3.0. Dressing percentage increased in G4, partially due to the increased shrink which resulted in the decreased fasted live weight previously discussed. Fat thickness at the 12th and 13th rib interface increased (P<.001) between each group with the largest increase in fat thickness occurring between G2 and G3, as expected, the feeding period in which the steers were switched to a high concentrate diet. Ribeye area increased between each group with the largest increase observed between G1 and G2. Calculated yield grades, using the equations of Murphy et al., 1960, did not differ (P>.10) between G1 and G2, but did differ (P<.01) between G2 and G3 and G3 and G4. Marbling scores and USDA quality grade scores were not different (P>.10) between G1 or GZ, and between G3 or G4, but differed (P<.01) between G2 and G3. Live weight (LWT) gains and empty body (EB) weight gains (Table 1-2) between Cl and G2 and G2 and G3, respectively, did nor differ (P>.10). However, live weight gain between G3 and G4 was only 74.9 kg. Average days on feed (64d) for each group did not differ between G1 and G2 and between G2 and G3 but was 55 d between G3 and G4. The average total days on feed for the duration of the study was 183 d. Average daily gain between groups did not differ (P>.10) but did decrease numerically as expected. TABLE 1-1. 69 MEANS AND STANDARD ERRORS FOR LIVE WEIGHT, EMPTY BODY AND CARCASS WEIGHTS AND CARCASS TRAITS Group 1 2 3 4 No. of steers 5 5 5 5 Trait Age 10 mo 12 mo 14 mo 16 mo Live fasted slaughter weight (LWT), kg 298.5 390.1 480.0 555.5 SE 2.99 2.09 .74 1.11 Empty body weight (EBWT), kg 273.9 358.4 440.0 514.9 SE 3.55 1.24 2.64 3232 EB WT as % __ __. of live weight, % 91.76 91.89 91.68 92.69“ SE .29 .54 '.54 ' .753' Hot carcass wt " -j; (HCWT), kg 188.1 247.5 303.7 365.7 SE 3.8 1.84 2.74 3.12 Dressing percentage, % 63.0 63.4 63.3 65.8 SE .10 .15 .07 .22 12th rib fat thickness, mm 2.6 4.8 8.7 11.4 SE .02 .03 .03 .05 Longissimus area, . cm2 60.3 75.2 80.8 86.6 SE .98 1.93 3.71 3.60 Kidney fat, % 2.0 2.5 2.5 3.1 SE .11 .16 .16 .19 Yield grade 1.74 1.82 2.39 3.01 SE .12 .16 .13 .18 Marbling scorea Trace 58 Trace 74 Small 12 Small 58 a Minimum traces = 0, maximum = traces 100. Traces = USDA Standard. Small = USDA low choice. ' 70 TABLE 1-2. MEANS AND STANDARD ERRORS FOR LIVE ANIMAL PERFORMANCE TRAITS AND LINEAR MEASUREMENTS Group Item 1 2 3 4 LWT gain between groups, kg 91.6 89.9 75.5 SE 1.87 .88 1.01 EBWT gain between groups, kg 84.5 81.6 74.9 SE 1.22 2.14 2.89 Average days on feed between groups 64 64 55 Total days on feed per group 64 128 183 SE 2.28 2.6 2.37 Average daily gain (ADG), LWT, kg 1.43a 1.4a 1.37a SE .03 .ll .05 Average hip height, cm 122.05 128.4 130.68 134.75 SE .43 .51 .55 .88 Frame score 5.43 _ 5.75a 5.5a 5.7a SE .06 .14 .10 .14 a Values within a row with a different superscript differ (P<.01). 71 Average hip height (a measure of growth used in conjunction with age to determine frame score) increased between groups. Frame score did not differ (P>.10) between groups 61 to G4, respectively. Empty body composition by percentages and weight is presented in Table 1-3. Mean percentage EB moisture (EBHZO) decreased from 60.9 (G1) to 52.3% in G4. Percentage EB fat (EBFAT) increased while percentage EB protein (EBP) decreased between each group through G3 but neither fat nor protein differed (P>.05) between G3 and G4. Percentage EB protein (EBP) decreased from 19.0 to 16.5% between Gl to G4, respectively. Percentage EB mineral (EBM) was 4.8% in Cl and decreased in each successive slaughter group to 4.0% in G4. The values for empty body composition of the steers in this study are similar to those reported by Haecker (1920) and Moulton (1922), however steers having similar EB composition in this study were 150 to 250 kg heavier than the cattle reported in their studies. As expected, the absolute weight of EBHZO, EBFAT, EBP and EBM (Table 1-3) increased between each group. However, as is apparent in Table 1-3, EBFAT changed the most dramatically, increasing 238% in weight, compared to a 61.5 and 63.1% increase in EBHZO and EBP, respectively. EBM increased in weight by 56.1% between 61 and G4. 72 TABLE 1-3. GROUP MEANS AND STANDARD ERRORS FOR EMPTY BODY COMPOSITION COMPONENTS Item 1 2 3 4 Empty body H20, % 60.9a 58.0b 54.0c 52.3C SE .33 .57 .70 .37 , Empty body fat, % 15.1a 19.5b 24.6C 27.1C SE .33 .85 .95 .49 Empty body protein, % 19.0a 18.1b 16.8C 16.5C SE .20 .20 .18 .12 Empty body mineral, % 4.8a 4.3b 4.2b 4.0b SE .16 .12 .11 .12 Empty body H20, kg 166.8 208.0 237.5 269.4 SE 2.76 1.55 3.48 3.27 Empty body fat, kg 41.3 70.0 108.2 139.6 SE .52 3.28 4.18 2.06 Empty body protein, kg 52.0 64.8 . 73.9 84.8 SE 1.04 .54 .88 1.04 Empty body mineral, kg 13.2 15.4 18.2 20.6 SE .51 .40 .38 .70 (P<.05). a,b,c Values within a row with different superscripts differ 73 Changes in carcass composition listed in Table 1-4 were similar to changes in EB composition. The absolute weight Of carcass moisture (CARCHZO) increased 69.3%, however, percentage CARCHZO decreased from 63.93 to 52.64% between G1 to G4, respectively. Absolute weight (kg) of carcass fat increased 290% and the percentage carcass fat increased from 16.87 to 32% between G1 and G4, respectively. Carcass protein increased 64.9% in absolute weight, but decreased as a percentage of carcass soft tissues from 18.1 to 14.5% between G1 and G4, respectively. Skeletal muscle increased in absolute weight (Table 1- 5) by 70.3% between G1 and G4. Skeletal muscle as a percentage of live weight and empty body weight (Table 1-5) decreased from 42.27:46.1% to 38.7:41.75% between (a. and G4, respectively. Carcass soft tissues (CST), as expected, increased with increasing carcass weight (Table 1-6). CST as a percentage of hot carcass weight increased between each group from 82.9 to 87.7% in G1 to G4, respectively. The increased CST retained in the carcass is an indicatiOn that adipose tissue and skeletal muscle increased at a more rapid rate than carcass bone. Carcass muscle increased in weight between each group, however, carcass muscle as a percentage of hot carcass weight decreased from 66.0 in Gl to approximately 58.0% in G4. The percentage carcass muscle of the steers in this study was similar to carcasses Of 74 TABLE 1-4. GROUP MEANS AND STANDARD ERRORS FOR CARCASS COMPOSITION Group Item 1 2 3 4 carcass H20, % 63.93a 59.53b 54.8C 52.64C SE .53 .77 .93 .68 Carcass EEL, % 16.87a 23.18b 29.28C 32.01c SE .40 .96 1.16 .77 Carcass Protein, % 18.11a 16.46b 15.11C 14.51C SE .30 .18 .25 .19 Carcass H20, kg 99.70 124.91 144.09 168.81 SE 3.09 .55 2.15 3.13 Carcass EEL, kg 26.3 48.66 76.99 102.62 SE .55 2.61 3.44 2.34 Carcass P, kg 28.21 34.56 39.7 46.53 SE 1.03 .31 .52 .66 a,b,c Values within a row with different superscripts differ (P<.05). 75 TABLE 1-5. GROUP MEANS AND STANDARD ERRORS FOR TOTAL SKELETAL MUSCLE, CARCASS SOFT TISSUE, CARCASS SKELETAL MUSCLE AND PERCENTAGE SKELETAL MUSCLE Group Item 1 2 3 4 Total skeletal muscle, kg 126.25 156.95 182.68 214.97 3.72 .58 2.81 2.69 Muscle percent of live weight, % 42.27a 40.24a 38.06b 38.70b SE . .84 .36 .55 . .53 Muscle percent of EB WT,% 46.09a 43.79b 41.51C 41.75c SE_, .56 .44 .54 .68 a,b,c Values within a row with different superscripts differ (P<.05). " 76 similar carcass composition reported by Callow (1961), Hendrickson et al. (1965) and Berg and Butterfield (1976). Carcass weights in their studies however, were 50 to 125 kg less than carcass weights in this study. The EB was comprised of 13.2% bone (actual bone and cartilage) in G1 (Table 1-7). EB soft tissues, as expected, increased more rapidly than EB bone between each slaughter group resulting in total EB bone accounting for 9.9% of the EB weight in G4. Carcass bone, as typically reported in the literature, consists Of actual bone, cartilage, heavy connective tissue, ligaments and tendons. The absolute weight (kg) of carcass bone comparable to carcass bone reported in the literature, is shown in Table 1-7. Actual carcass bone and cartilage (without heavy connective tissue, ligaments and tendons) for steers in each group in this study was reorted by Schroeder (1987). Percentage carcass bone (including heavy connective tissue, ligaments and tendons) was 17.07% in G1 decreasing to 12.3% in G4, respectively. These data follow similar patterns Of development for British-bred cattle as discussed by Callow (1961), Lawrence and. Pearce (1964), Henrickson et al., (1965) and Berg and Butterfield (1976). Carcass muscle to bone ratios (carcass bone including heavy connective tissue, ligaments and tendons) in this study were 3.88, 4.15, 4.4 and 4.7 for G1 to G4, respectively. These data were similar to reports in the 77 TABLE 1-6. GROUP MEANS AND STANDARD ERRORS FOR CARCASS SOFT TISSUE, CARCASS SKELETAL MUSCLE, PERCENTAGE SKELETAL MUSCLE, CARCASS BONE AND PERCENTAGE CARCASS BONE Group Item 1 2 3 4 Carcass soft tissues (CST), kg 156.0 209.9 262.9 320.7 SE 3.99 2.43 2.28 2.66 CST % of HCWT, '82.87 84.93 86.51 87.69 SE .47 .59 .37 .38 Carcass skeletal muscle, kg 124.20 154.49 179.72 211.74 3.68 .46 2.76 2.72 CarcaSstuscle percent of carcass weight, % 66.0a 62.51b 59.19C 57.89C .72 .52 1.01 .47 a,b,c Values within a row with different superscripts differ (P<.05). 78 literature by Luitingh (1962), Henrickson et al. (1965), Berg and Butterfield (1966:1976), Jones (1985b,c) and Lunt et al. (1985a,b), but are consistently lower than those reported by Shanin and Berg (1985a,b,c,) for double muscled, "synthetic" beef (Galloway x Angus x Charolais crossbreds) and small framed British breeds. Complete physical dissection of the entire EB and carcass allowed for determinations of numerous relationships found in Table 1-8 between skeletal muscle, skeletal muscle protein, empty body protein and carcass protein. Dissection and chemical analyses of the skeletal muscle and EB determined that across all slaughter groups, G1 to G4, respectively, the percentage of the EB protein pool attributable to skeletal muscle protein was constant (P>.10) between groups averaging 52% ikn: all steers. Protein content in all skeletal muscle free Of external fat was constant (P>.10) at 21.0% (Table 1-8), although there was a slight numerical decrease in protein content as each slaughter group increased in weight. Dissection. and. chemical analyses of 'the carcass skeletal muscle and other carcass soft tissues (CST) showed that when protein content Of the CST was determined in each group, 95.0% of all protein present in the CST was accounted for in the carcass skeletal muscle. These relationships can be useful in predicting EB and carcass composition as described in later chapters. 79 TABLE 1-7. GROUP MEANS AND STANDARD ERRORS FOR PERCENTAGE TOTAL EMPTY BODY BONE, TOTAL CARCASS BONE WEIGHTa, AND PERCENTAGE BONE IN THE CARCASS AND MUSCLE TO BONE RATIO Group Item 1 2 3 4 Total bone only of EBWT, % 13.20a 11.48b 10.46bC 9.87C SE .18 .32 .18 .22 Total carcass bone, kg 32.06 37.27 40.80 45.04 SE .46 .94 .74 1.35 Total cargass bone, % 17.07a 15.08b 13.43bc 12.31C SE .47 .44 .18 .32 Carcass bonee % 15.1a 13.31b 12.05bC 11.14C SE .31 .42 .13 .31 Carcass muscle/bone ratio 3.88a 4.15b 4.41c 4.71C SE .15 .09 .05 .11 a,b,c Values within a row with different superscripts differ (P<.05). d Includes heavy connective tissue, ligaments and tendons. e Includes only carcass bone and cartilage. f Carcass bone including heavy connective tissue, etc. TABLE 1-8. GROUP MEANS FOR PERCENTAGE PROTEIN IN SKELETAL MUSCLE AND PERCENTAGE OF SKELETAL MUSCLE PROTEIN IN TOTAL CARCASS PROTEIN Group Item 1 2 3 4 Percentage of EB protein from skeletal muscle, % 52.0a 51.4a 51.41a 52.9a SE 1.27 .61 .44 .23 Protein in skeletal muscle, % 21.4a 21.2a 20.8a 20.9a SE ‘ .24 .20 .14 .20 Skeletal muscle protein as % of carcass P 95.0a 95.03a 94.3a 95.2a SE .14 .12 .29 .13 ab Values within a row with different superscripts differ (P <.05). 81 Percentage lean body mass decreased with increasing live weight (Table 1-9). However, consistent with reports by Byers (1979b) and Arnold et a1. (1985) the ratio Of EBHZO to lean body mass remained relatively constant (P>.10) averaging .72 in steers weighing 300 to 555 kg. Likewise, the EBP:EBH20 and EBH20:EBP ratios remained constant averaging .312 and 3.21, respectively, across all slaughter groups. Interestingly, the carcass moisture to carcass protein ratio did not differ (P>.10) averaging 3.62 in steers with greater than 20% carcass fat (62 to G4, respectively). The skeletal muscle moisturezprotein ratio also remained constant (P>.25) at 3.55 across all groups. gpmpggipign Q: ggipy Steers in this study gained the least amount Of EBF (Table 1-10) and the most EBP during the first 64 d feeding period. EBF gain per day was 446 g, accounting for 33.8% of the EB average daily gain (ADG). EBP gain per day was about 200 g which accounted for about 15% Of the EB ADG for the feeding period. EBF gain was the greatest during the second 64d averaging 597 g/d, about 47% of the EB ADG. During this same period, EBP gain was the least averaging 142 g/d, only 11.1% of EB ADG. This is not totally unexpected since the steers were switched from a high protein, lower energy diet to a lower protein, high concentrate diet during this period. The switch to lower protein and higher energy in the diet may have partially accounted for more lipid being synthesized and accumulating 82 TABLE 1-9. GROUP MEANS AND STANDARD ERRORS FOR ACTUAL LEAN BODY MASS AND RELATIONSHIPS OF WATER TO PROTEIN IN THE EMPTY BODY, CARCASS AND SKELETAL MUSCLE Group Item 1 2 3 4 Actual lean body mass, % 84.69 80.41 74.91 72.78 SE .32 .85 .88 .49 EBH20:LBMASS .719a .7216a .7204a .7188a SE .003 .002 .002 .002 EBP:EBH20 .3119a .3117a .3113a .3147a SE -.004 .002 .002 .003 EBH20:EBP 3.21a 3.21a 3.21a 3.188 SE .04 .02 .02 .03 Carcass moisture: carcass protein ratio 3.53b 3.61a 3.63a 3.63a SE . .04 - .05 .02 .03 Skeletal muscle moisture:protein ratio 3.54a 3.55a 3.55a 3.52a SE . .03 .04 .03 .06 ' a Means in a row with different superscripts differ (P<.05). 83 in the abdomen and carcass. During the final 55 d feeding period (d 128 - 183), the steers gained 573 g/d of EBF accounting for 42% of the EB ADG, slightly less than the previous period. EBP gains, however, were higher than during the previous 64 d period, probably due to compensatory protein deposition when the temperatures in the feeding period of late summer were more temperate and growth performance was enhanced. When EBF deposition per day was calculated during the last 119 d Of feeding (typical of many feeding trials), grams of EBF gained per day was 585.9 g and EBP gained per day was 167 g. These values were in a range consistent with the estimated daily values of McCarthy (1981) and Anderson (1987). Table 1-11 contains the carcass composition Of gain data for the steers in this study. During the first 64 d period, steers gained approximately 349 g; of carcass fat per day which was 78% of EBF gain for this feeding period. Carcass protein gain was about 100 g/d or about 50% of the EBP gain. Interestingly, the deposition Of carcass fat during the second 64 d period was reduced to 443 g/d, 74.1% Of the EBF gain. This decrease in the rate Of carcass fat deposition seems abnormal, however, little information exists in the literature which examines by physical carcass dissection, the effects of switching to a high concentrate diet during the feeding Of cattle. Closer examination of the data indicates that during the feeding period in which 84 HPwfim HIHO. we UHfiwmwMZH UVKm OZ MMMU MEMHK wOUK EVE VZU DNOHMHZ WOONMHHOZ wmezmmz mfiwdmmflmw QwOCwm Hdwa omwm Os mama mm and. so mm mmd amps. Q\Q w mm V00 mm phonmea. we mm pnonmeb owes. Q\Q w mm V00 Olmp mblwwm melew olHNm Oleu mAIHmu mm.mm um.~w wH.e® mm.vm mm.NN mm.qw Anm.~m wee.wb mum.m mNH.m www.0m mmm.m uw.mH em.mv AN.H eo.H¢ bo.mm be.mm Hw.vm 0.0m Ho.mw NH.mm wN.uH H@.©N Hmm.m How.ow Hmo.®H qu.®p Hum.wo Haw.» Hm.Hp HH.H Ho.bm Hw.Hm Harm» HN.uu 85 the steers were switched to a high concentrate diet more fat was deposited in the other EB tissues, namely the gastrointestinal tract viscera. The deposition of carcass protein during the same period was also lower during the second 64 d feeding period. The carcass protein deposited, however, accounted for 56.5% of the EBP deposited per day. Carcass fat deposited was 466 g/d, 81.4% of the EBF deposition during the final 55 d period. As with EBP deposition, carcass protein deposition increased over the second 64 d period to 124 g/d; 63.1% of the daily EBP deposition. Skeletal muscle deposition rates varied as would be expected over the duration of the study (Table 1-12). Over the entire study (183 d) the average skeletal muscle deposited per day averaged 484.7 g. Closer examination of Table 1-12, however, indicates that during the second period (d 64 - 128) skeletal muscle accretion was reduced at the time when EBF depostion (Table 1-10) was greatest. During the final 55 d feeding period skeletal muscle deposition was increased tO the highest rate Of 587.3 g per day. During this period there appeared to be compensatory muscle deposition. Part Of this increased skeletal muscle deposited, however, was actually fat being deposited in the muscle in the form of intramuscular adipose tissue. During the final feeding period, skeletal muscle deposition accounted for 43.2% of the EB ADG. 86 fl>whm HIHH. van>mm w>8 #20 VWOBMHZ >OONNHHOZ UMHSMMZ mfivcmmflww Qwocwm We UHMwmwMZB U>Km 02 mmwc Down on Home HWOB Ola» mAIHNm HNmIHmw OIHNm OIHmu mélpmu omnommw nun. we -.uu um.uu ~m.mw mo.mm um.u~ mu.om nmnommm mun omen. Q\Q wom.o bo~.mm omm.o wom.um opu.om omu.s w mm mmn moondeOD um.Hm us.HH mw.s um.om uu.mm uu.uo omnowmm pnonmws. we m.um m.ws m.mu Hp.so Hm.u~ Hp.mu omnommm pnonmws owes. o\a oo.- mo.uw Hue.» mo.m Hoo.HH Hoo.mo x mm pnonmw: moonmnwos oo.u mm.m mu.H m~.m mm.o mo.H 87 Table11-13 contains the composition makeup as a percentage, Of the EB by each major tissue. As previously discussed, skeletal muscle as a percentage of the EB decreased in each successive group, however, skeletal muscle was the largest portion of the EB in each group. Total bone (cartilage and bone) also decreased as a percentage Of the EB. Hide as a percentage of the EB remained relatively constant at about 8% Of the EB weight in each slaughter group. Blood decreased slightly as a percentage of the EB in each successive group. Accurate quantitation Of blood, however, is difficult since a portion of the blood is retained in capillaries causing an underestimation Of blood and overestimation Of other tissues which had trapped blood. The gastrointestinal tract remained relatively constant between 9.5 and 10.0% of the EB weight in each group. Nonskeletal muscle EB soft tissues (EBST),(EB and carcass), comprised mainly of adipose tissue, not surprisingly, showed the largest change as a percentage of EB weight. EBST increased from 15.4 to 24.4% of the EB weight as the steers increased in weight and degree Of fatness. The composition Of each previously mentioned EB tissue and the percentage each tissue contributed to EB moisture, fat and protein is found in Appendix Tables 6, 7, 8, 9 and 10. 88 evwfim HIHN. MSWHK wOOK mNMEHHVH SdmObw POOwMHHOZ wMHZMMZ mfiwcomemw ONOGwm >6 UHmwMNMZB vam 02 MMHU omwm 0: Moon Hume cums molpmm melpmw onwwm onwmu molwmu mm mwmwmnmw Scmowm. Wm uo.u mm.w u~.u . mm.6 mm.q no.0 so many scmowm owes. o\o 666.6 6op.m mmo.o 660.6 6m6.o 684.6 & Om mm >00 wm.w wH.wm pw.Hm wu.m wm.w uV.H 89 TABLE 1-13. iMEANS OF PERCENTAGE OF EMPTY BODY COMPOSITION FROM MAJOR EMPTY BODY TISSUES Group Item 1 2 3 4 Skeletal muscle, % 46.09 43.79 41.51 41.75 SE .56 .44 .54 .68 Total EB bone, % 13.2 11.48‘ 10.46 9.87 SE .18 .32 .18 .22 Hide, % 7.97 8.65 8.09 8.15 SE .29 .22 .14 .11 Blood, % 5.74 5.5 5.27 4.56 SE .19 .20 .28 .06 GI tract, % 9.48 9.62 10.0 9.76 SE .27 .34 .28 .48 Empty body and carcass nonskeletal muscle soft tissues, % 15.4 18.98 22.93 24.37 SE .47 .51 .29 .46 Respiratory tract, % .93 .87 .73 .70 SE .06 .03 .04 .04 Heart, % .54 .52 .48 .43 SE .02 .02 .02 .02 Central nervous system, % .21 .18 .17 .14 SE .02 .015 .03 .02 Urinary/ reproductive tract, % .41 .40 .36 .27 SE .03 .007 .002 .004 SUMMARY Complete physical dissection and chemical analysis of all EB and carcass tissues Of 20 genetically similar steers at four developmental stages was conducted in this study. The continental European crossbred steers in this study were heavier in weight but similar in composition to studies reported earlier. Five steers were slaughtered per weight group when the fasted live weight was estimated to be 300, 390, 480 and 570 kg for Gl, G2, G3 and G4, respectively. EB weight as a percentage Of live weight was 91.8, 91.9, 91.7 and 92.7% for G1 to G4, respectively. Average daily gain, although decreasing slightly, did not differ (P>.10) between slaughter groups. Frame scores for steers in each group did not differ (P>.10) ranging from 5.4 to 5.75. Percentage EB moisture (EBHZO) and protein (EBP) decreased from 60.9:19.0 in 61 to 52.3:16.5% in G1 to G4, respectively. Percentage EB fat (EBFAT) increased from 15.1 to 27.1% in G1 to G4, respectively. Carcass moisture and protein decreased from 63.9:18.11 in G1 to 52.64:14.51% in G4, respectively. Carcass fat increased from 16.87 in G1 to 32.01% in G4, respectively. Total skeletal muscle increased from 126.25 in 61 to 215 kg in G4, respectively. Skeletal muscle as a 90 91 percentage of live weight. and EB weight decreased (P<.05) from 42.3:46.09 in GI to 38.7:41.75% in G4, respectively. Carcass skeletal muscle decreased (P<.05) from 66.0 to 57.9% from Gl to G4, respectively. Carcass soft tissue (includes muscle and fat) as a percentage Of hot carcass weight increased from 82.9 to 87.7% from Gl to G4, respectively. Percentage empty body bone (connective tissue, ligaments, tendons, etc. not included) decreased from 13.2 to 9.87% from Gl to G4, respectively. Total carcass bone (including connective tissue, ligaments, tendons, etc.) increased in weight from 32.06 to 45.04 kg from Gl to G4, but decreased as a percentage of the carcass between Gl and G4 (17.07 vs 13.43%), respectively. The carcass muscle to bone ratio also increased from 3.88 in 61 to 4.71 in G4 indicating that skeletal muscle was increasing in weight at a more rapid rate than carcass bone. Percentage lean body mass (LBMASS) decreased from 84.7 to 72.8% between Cl and G4, respectively. EBH20:LBMASS remained constant across all groups at .72. Likewise, EBH20:EBP remained constant across all groups at 3.2. The carcass H20:carcass protein ratio was 3.53 in G1 but increased and remained constant at about 3.63 in (:2 to G4, respectively. The skeletal muscle moisture:protein ratio did not differ (P>.10) between groups ranging from 3.52 to 3.55. 92 Several previously' unreported relationships were determined from this study. 1) 52% of empty body protein is derived from skeletal muscle and 2) 95% of carcass soft tissue protein is accounted for in the skeletal muscle Of the carcass. These relationships and others identified in this study can be useful in understanding and predicting changes in empty body and carcass composition Of cattle typical Of today's feedlot. EB fat gain (g/d) was greatest and EB protein gain (g/d) was the least during the feeding period d 65 to 128 averaging 597.3 and 142.03 g, respectively. EB fat gain (g/d) was 537.0 from d 0 to 183. EBP gain (g/d) was 178.7 from d 0 to 183. EB fat gain as a percentage of EB ADG was about 40-41% for the 183 d feeding period. EBP gain as a percentage of ADC was 13.5% for the 183 d feeding period. Carcass fat gain increased between each group with the greatest carcass fat gain (g/d) during the 128-183 d period averaging 466.0 g. Carcass fat gain (g/d) as a percentage of EB fat accretion during the 0-183 d period was 77.7%. Carcass protein gain (g/d) was 100.1 9 during the 0-183 d feeding period, but varied considerably during- the individual feeding periods. Carcass protein as a percentage of EB protein accretion was 56.0 for the 0-183 d feeding period. Skeletal muscle gain (g/d) was 36.7% Of EB ADG for the entire feeding period. 93 The hide and gastrointestinal tract as a percentage of EB weight did not differ (P>.10) between groups. The hide accounted for about 8% of the EB weight in each group. The gastrointestinal tract (including associated fat) accounted for between 9.5 and 10% Of the EB weight in each group. The greatest change in composition of dissectible tissues occurred in the EB and carcass nonskeletal muscle soft tissues (mainly adipose tissue) which increased from 15.4 to 24.4% of EB weight. All other tissues decreased as a percentage Of EB weight between groups. Chapter 2 Use of Deuterium Oxide Dilution Techniques to Estimate Skeletal Muscle Protein 94 ll.-- '1. '1'» I'll! . ABSTRACT Body composition estimated. by’ one and two pool compartment deuterium oxide (D20) dilution techniques was compared with body composition determined directly on twenty large framed continental European crossbred steers. Five steers were infused with D20 before slaughter at one Of four weights (300, 390, 480 and 560 kg live weight). Empty body water (EBHZO) was overestimated by both the one compartment (1CM, using slope, intercept method) and the two compartment kinetic (2CM) method in steers at 300 to 390 kg. At 480 and 560 kg, EBHZO was overestimated by 2.5 to 5.0% by both the 1 CM and 2 CM methods, however, the 1CM did not differ statistically from the direct method. Empty body protein (EBP) estimated by the 1CM did not differ statistically from direct methods, however, EBP was overestimated by 1.5 to 6.5% across all weight groups. In most cases the 2CM overestimated (P<.05) EBP in most cases from 2.0 to 10.0%. Empty body ether extract (EBFAT) was underestimated (P<.01) by both the 1CM and 2CM methods at 300 and 390 kg. EBFAT estimated by 1CM in steers at 480 and 560 kg was not statistically different from actual empty body fat, due to large standard errors, but was 8 to 9% less than actual. The 2CM method underestimated (P<.05) EBFAT in all groups by 13 to 30 %. Percentage gut fill did 95 96 not differ (P>.05) between direct and estimated fill in 300, 390 and 480 kg steers, however, large estimated variation was found at 560 kg steers. In general, both the 1CM and 2CM were not useful in accurately estimating empty body composition in crossbred steers at 300 to 390 kg. Both the 1CM and 2CM methods were somewhat more useful, although not accurate, in estimating empty body composition in steers at 480 or 560 kg. The assumptions that the amount Of EBHZO associated with EBP and ash were valid, however, values from this study differed slightly from previous studies. In animals with empty body weight greater than 175 kg, the calculated values from the literature for the ratios Of pmetein and ash to water are .302 and .0668, respectively. In this study the ratio Of EBP:EBH20 and EB ash:EBH20 was .312 and .0755, respectively. The ratio Of skeletal muscle protein to empty body protein was constant in all weight groups with a value of .52. 'The relationship between EBHZO and skeletal muscle protein can be useful in future studies investigating skeletal muscle growth using repeated indirect methods for estimating EBHZO and EBP. Skeletal muscle protein (kg) can be estimated by the following equation: -2.11 + .172 x EBHZO (kg) with R2=.97 and RSD = 1.18. Results Of this study suggest developmental changes occur in EBH2O to D20 relationships as cattle mature and fatten. In order to accurately predict EBP, developmental 97 interactions between EBHZO and 020 space must be accounted for when developing prediction equations. INTRODUCTION The accurate estimation of body composition and skeletal muscle of live animals has understandably attracted much attention. An accurate estimate of body composition and muscle mass would be extremely useful in studies to examine the rate of accretion and changes in chemical components in the body. Whole body analysis, while most accurate, is laborious, expensive and does not allow for repeated measurements. As indicated by Ferrell and Jenkins (1984), an ideal method of predicting body composition should be accurate, repeatable, easily performed, relatively inexpensive, applicable to animals of diverse ages and done with minimal distress to the live animal. Numerous research studies efforts have been attempted and methods developed to estimate carcass composition of cattle and other species. The most widely used include: component parts which have been examined for potential use as composition predictors (Hopper, 1944; Hankins and Howe, 1946: Hinks and Prescott, 1974: Ferrell et al., 1976) and specific gravity (Garrett and Hinman, 1969: Preston et al., 1974, Jones, 1985a) which have had varying success. Concurrently, substantial efforts have been made to measure composition Of the live animals using a variety of 98 99 procedures. Numerous measurements Of body composition involve the relationships between the chemical components water, protein and fat. While protein and mineral mass have been measured by creatinine excretion (Boileau et al., 1972: Aulstad, 1970) and isotopes, e.g., potassium (40K, 42K Lohman et al., 1966; 1968; McLellean et al., 1969: Frahm et al., 1971), the relationships involving water, the largest component in the empty body, especially the lean empty body, have been the most frequently studied. A number of investigators have conducted experiments using urea dilution (Preston and Kock, 1973; Hammond, 1984), 42K dilution (Trigg et al., 1978), dye dilution (Panaretto and Till, 1963), antipyrine (Wellington et al., 1956) and other infusates which are based on dilution principles to estimate body water and (or) fat. Further technological advances have allowed for use of the hydrogen isotopes, namely, tritium (TOH) and deuterium oxide (D20) as more ideal tracers for estimating body water (Foot and Greenhalgh, 1970; Searle, 1970a; Crabtree et al., 1974: Donnelly and Freer, 1974; Robelin, 1977: Byers, 1979b: Little and McLean, 1981: ArnOLd et al., 1985, Miller et al., 1988). However, none of these methods is without problems, which has been thoroughly discussed in the review of literature. Application of the biological nonradioactive tracer D20, is frequently used today in body composition studies. 100 However, use Of this technique is complicated by the direct passage of 020 into the ruminal water in the gastrointestinal tract (GITHZO) of cattle and sheep, thus causing overestimations of total empty body water. Sheng and Huggins (1979) discussed the relationship between tissue water and the lean body mass (LBM). Because tissue water is mainly associated with the lean body, generally accepted relationships between empty body water (EBHZO), empty body protein (EBP), fat (EBFAT) and ash (EBM) have been established and used to calculate the water, protein, fat and ash in the empty body (Byers, 1979b: Loy, 1983). Several authors have reported successful development of hydrogen isotope dilution techniques to estimate EBHZO and digestive tract fill of cattle from calves to cows and in cows of various breeds. Other studies report variable results and minimal ability to predict carcass fat (Byers, 1979b; Ferrell and Jenkins, 1984; Odwongo et al., 1984; Arnold et al., 1985: Martin and Ehle, 1986, Miller et al., 1988). Arnold et al. (1985) discussed three approaches used in developing mathematical models to determine body water after injection of a tracer. The commonly used methods in ruminants are modifications Of the one pool technique of Robelin (1975) and the two pool technique developed by Byers (1979b). Further refinement Of the previously mentioned techniques is necessary in order to validate the “h. 101 procedures to gain widespread acceptance. Berg and Butterfield (1976) recommended that muscle mass be the logical endpoint for the beef industry. While considerable data exist which examine the yield of saleable retail cuts from carcasses ( Harrington, 1971; Abraham, 1968,1980: Parrett et al., 1985; Johnson et al., 1989) and to a lesser extent the total separable muscle from carcasses (Butterfield, 1962; Cole et al., 1960b:1962: Allen, 1966: 1968: Berg and Butterfield, 1966: Jones, 1985a: Shanin and Berg, 1985a,b,c), relatively limited amounts of data exist which examine the relationship between muscle mass, skeletal muscle protein and EBP. Haecker (1920) performed extensive dissections of the whole body of cattle, reporting EBP found in the "flesh" (muscle and fat) Of cattle ranging from 45 kg calves to 682 kg steers. Other more recent work (Byers, 1979b; Little and McLean, 1981; Ferrell and Jenkins, 1984) has been limited to the determination of EBP without detailed dissection Of skeletal muscle and. determination. Of jprotein associated with skeletal muscle. The Objective Of this study was to determine the relationship between skeletal muscle protein and empty body protein. A second Objective Of this study was to examine the use Of one pool and two pool isotopic dilution methods and existing equations, utilizing D20 as a tracer, for estimating empty body protein and skeletal muscle of steers “-nu- 102 at four developmental stages Of growth. MATERIALS AND METHODS Twenty genetically similar continental European cross- bred beef steers were used in this study. Animals were randomly allotted to one of four slaughter weight groups, Gl to G4, (300, 390, 480, 560 kg, live weight), designed to represent animals at four developmental stages. The final weight group was to represent the finished market weight and amount Of fat which is considered within the Optimal range for steers in today’s market. The management and diets of the animals was the same as that pmeviously described. Predicted empty body composition Of the steers in this study was determined using a modification of the procedure described by Byers (1979b). When the animals reached the designated weight they were restrained in a squeeze chute, haltered and catheterized. Animals were held Off feed 16 h before the time of infusion to reduce excessive fill, but water was never restricted. A 50 cm length of polyethylene tubing (PE200, 1.0. 1.4mm) was passed through a 12 gauge needle into the jugular vein. The needle was removed, the tubing fitted with a 17 gauge adapter, flushed with either 3% citrate solution or heparinized saline and plugged. Deuterium oxide (D20, 99.8%, Cambridge Laboratories, MA) was used as the tracer 103 104 after 9 9 NaCl per liter were added to give a physiological infusate. The quantity infused was 10 g/ 45 kg body weight, which was sufficient to give an initial D20 concentration of 400 to 650 ppm. Sixty ml syringes were filled with D20 and weighed. Prior to infusion an initial blood sample was drawn (To), to determine background concentrations of DZO in each animal. Blood was stored in labeled 15 ml plastic heparinized tubes with rubber stoppers or plastic caps. After collections were completed each day, the samples were frozen at -30° C for later processing. At the beginning of each initial infusion, the catheter was flushed and D20 quickly infused with the beginning and ending times recorded (to the nearest .01 min). The times were averaged to arrive at an initial infusion and all subsequent samplings determined from this time. To ensure complete delivery of D20 the catheter was flushed with 50 ml of saline solution. TO prevent clotting, 10 to 15 ml of 3% citrate solution were infused and then the catheter was plugged. Syringes were weighed immediately after infusion to the nearest .01 g to determine actual dosage. After the infusion procedure was completed, blood samples were drawn at 10, 15, 20, 25, 30, 45, 60, 75, 90, 105, 120, 180, 240 and 300 min. The remaining samples were taken at 24 h (1440 min), 48 h (2880 min), 72 h (4320 min). The 120 min and later samples were taken by venipuncture. 105 For all samples, an initial 15 ml blood sample was drawn and discarded to remove residual H20 and citrate from the tubing. The start and end Of bleeding times were averaged to arrive at an actual bleeding time. After the 120 min sample was taken, the animals were returned tO the pens and allowed access to feed and water. Animals were weighed at the beginning of the infusion and when the 3, 4, 5, 24, 48 and 72 h samples were taken to Obtain an average live weight. All frozen blood samples were thawed, transferred to 100 ml volumetric flasks and lyophilized. Recovered D20 samples were refrozen at 0°C in 20 m1 serum bottles until analyzed. All samples were analyzed for D20 via infrared spectrophotometry, using procedures described by Byers (1979a). Water kinetics were examined by two methods. The two pool (2CM) standard curve peeling process of Byers (1979b) was used with several modifications. The doses of D20 infused were corrected for NaCl by multipling the infused amount by .991. Further adjustment to the pool sizes was made for the difference in the density Of D20 to H20 by dividing by 1.1044 to determine QAW (defined as EBHZO) and QBW (defined as gastrointestinal water, GITHZO). These corrections increased the accuracy Of the procedures. The second method was a one pool method (1CM) described by Loy (1983) and evaluated by Arnold et al. (1985). Modifications and adjustments to this procedure were the same as previously mentioned for the two pool method. 106 Examples of the equations for the two pool kinetics system were presented by Byers (1979b) and McCarthy (1981). Following completion of the sampling at 72 h the animals were transported to the meat laboratory and slaughtered. All tissues were individually collected, weighed and later analyzed for moisture, protein (nitrogen x 6.25) and ether extractable lipid (EEL). The right side of each carcass was physically separated into muscle, fat depots, heavy connective tissue and bone. The soft tissues were ground three times through a 3 mm plate, subsampled and powdered. All bones (including skull and feet) were weighed individually and as groups, and then frozen. Bones were ground through an Autio 801 grinder at The Ohio State University, subsampled and analyzed. The tail was weighed and ground through an 8 mm plate, subsampled and powdered. One side of the hide was ground for analyses. viscera was emptied of contents which were then pooled, weighed and subsampled. Individual viscera components, organs, internal (noncarcass) fat depots and all other internal body cavity components were ground, powdered and analyzed. All tissues collected were summed after analyses to derive empty body' weight (EBWTO. Empty body and carcass composition components were determined from the weight Of each individual sample and the resulting percentage composition. Skeletal muscle weight and moisture, EEL and protein percentages were determined. 107 Means and standard errors for all EB and skeletal muscle components were calculated for each group of animals. Analysis of variance was used to examine differences in composition between dilution methods. Equations predicting’ skeletal 'muscle, empty' body' water, empty body protein and empty body fat were derived using stepwise regression procedures according to the SPSS Base Manual (1989). RESULTS Empty body weights (EBWT) and EB composition data for the four slaughter groups (61 to G4) are shown in Table 2- 1. As expected as the weight of all components increased during development, the percentage of empty body moisture (EBHZO), protein (EBP) and mineral (EBM) decreased (P<.001) while EBFAT increased. Table 2-2 contains the lean body mass (LBM:kg) and percentage LBM for each group. As the steers matured, the absolute weight Of the LBM increased but the percentage Of LBM decreased 5.05, 6.8 and 2.8%, respectively, indicating each successive group deposited an increasing amount of fat. The ratio of EBHZO to LBM did not differ (P<.001) between groups and remained constant for all groups at 72.0%. The relationship of EBP:EBHZO and EBH20:EBP also remained constant (P<.001), averaging .312 and 3.21 for all steers. Table 2-3 gives the means and standard errors Of the actual and predicted EBWT for 1CM and 2CM methods. EBWT in 61 was slightly overpredicted (P<.05) by the 1CM and 2CM method, by 1.4 and 2.7%, respectivelyu As weight increased, both. methods improved (statistically) in accuracy (except in G3 for 1CM: P<.05) tO estimate EBWT. However, both methods overestimated EBWT in G2 and G3 from 108 109 TABLE 2-1. GROUP MEANS AND STANDARD ERRORS FOR ACTUAL EMPTY BODY COMPOSITION COMPONENTS Group Item 1 2 3 4 Actual empty body weight, kg 273.9 358.4 440.0 514.9 SE 3.55 1.24 2.64 3.32 Empty body H20, kg 166.8 208.0 237.5 269.4 SE 2.76 1.55 3.48 3.27 Empty body H20, % 60.9 58.0 54.0 52.3 SE .33 .57 70 .37 Empty body fat, kg 41.3 70.0 108.2 139.6 SE .52 3.28 4.18 2.06 Empty body fat, % 15.1 19.5 24.6 27.1 SE .33 .85 .95 .49 Empty body protein, kg 52.0 64.8 73.9 84.8 SE 1.04 .54 .88 1.04 Empty body protein, % 19.0 18.1 16.8 16.5 SE .20 .20 .18 .12 Empty body mineral, kg 13.2 15.4 18.2 20.6 SE .51 .40 .38 .70 Empty body mineral, % 4.8 4.3 4.2 4.0 SE .16 .12 .11 .12 110 TABLE 2-2. GROUP MEANS AND STANDARD ERRORS FOR ACTUAL LEAN BODY MASS AND RELATIONSHIPS OF EMPTY BODY PROTEIN TO EMPTY BODY WATERa Group Item 1 2 3 4 Actual lean body mass, kg 231.97 288.21 329.64 374.74 SE 3.87 2.31 4.23 4.58 Actual lean body mass, % 84.69 80.41 74.91 72.78 SE .32 .85 .88 .49 EBH20:LBMASS .719a .7216a .7204a .7188a SE .003 .002 .002 .002 EBPzEBHZO .3119a .3117a .3113a .3147a SE .004 .002 .002 .003 EBH20:EBP 3.21a 3.21a 3.21a 3.18a SE .04 .02 .02 .03 __— a Means in a row with different superscripts differ (P<.05). 111 .8 to 2.6%. In G4 the 1CM tended to overestimate EBWT (P>.05) by 1.05% and the 2CM method tended to underestimate (P>.10) by .9%. Group means and standard errors for the percentage of EBHZO from actual and prediction methods are presented in Table 2-4. The 1CM overestimated (P<.05) EBHZO in Cl and G2 by 8.2 and 7.5%, respectively. Estimation of EBHZO by the 1CM method tended to improve as the EBWT increased (P>.05). However, EBHZO was still overestimated by 5.0 and 2.5% in G3 and G4, respectively. The 2CM overestimated EBHZO (P<.05) in all groups by 8.9, 8.9, 11.9 and 6.35%, respectively. Predicted EBP (Table 2-5) using 1CM was not statistically different from direct measurements, although EBP was overpredicted in each group by 1.5, 2.3, 2.7 and .7%, respectively. The 2CM method did not accurately predict EBP in the young, lean steers in Gl, 62 and G3, as it overestimated EBP by 5.3, 5.4 and 8.5%, respectively. The 2CM estimated EBP did not differ (P>.05) from the actual EBP in G4 but was overestimated by 1.9%. Estimated empty body fat (EBFAT) presented in Table 2-6 was underestimated (P<.01) by both prediction methods. The 1CM underestimated EBFAT by 27.1, 21.4, 8.2 and 9.1% for the respective group. The 2CM method underpredicted EBFAT to a greater extent in each group by 39.3, 31.5, 29.9 and 12.6%, respectively. It is interesting to note, however, that as the steers fattened, both methods improved in the ability to estimate fat content. 112 TABLE 2-3. GROUP MEANS AND STANDARD ERRORS FOR ACTUAL EMPTY BODY WEIGHT AND EMPTY BODY WEIGHT DETERMINED BY D20 METHODSa Group Item 1 2 3 4 Actual empty body weight, kg 273.9a 358.4a 440.0a 514.9a SE 3.55 1.24 2.64 3.32 020 1 pool empty body weight, kg 277.7b 365.5a 451.4b 520.3a SE 3.39 2.83 1.43 1.42 DZO 2 pool empty body weight, kg 281.3b 361.1a 445.96a 510.5a SE 3.19 4.63 3.96 3.96 a Means in a column with different superscripts differ (P<.05). 113 TABLE 2-4. GROUP MEANS AND STANDARD ERRORS FOR PERCENTAGE AND WEIGHT OF EMPTY BODY WATER DETERMINED BY DIRECT AND 020 METHODSa Group Item 1 2 3 4 Actual empty body H20, % 60.88a 58.03a 53.97a 52.31a SE .33 .57 .70 .37 D20 1 pool Eggfy8b0dy 65.84” 62.38” 56.68a 53.61a SE .93 1.25 1.56 .66 D20 2 pool figgfy%b°dy 66.28” 63.20” 60.38” 55.63” SE .59 .87 1.31 .89 —5 Means in a column with different superscripts differ (P<.05). 114 TABLE 2-5. GROUP MEANS AND STANDARD ERRORS FOR PERCENTAGE AND WEIGHT OF EMPTY BODY PROTEIN DETERMINED BY DIRECT AND D20 METHODSa Group Item 1 2 3 4 Actual empty body protein, % 18.99a 18.09a 16.80a 16.46a SE .20 .20 .18 .12 DZO 1 pool empty body protein, % 19.27a 18.51a 17.25a 16.57a SE .21 .28 .35 .15 D20 2 pool empty body protein, % 20.0” 19.07” 18.22” 16.78” SE .18 .26 .39 .27 a Means in a column with different superscripts differ (P<.05). 115 TABLE 2-6. GROUP MEANS AND STANDARD ERRORS FOR PERCENTAGE AND WEIGHT OF EMPTY BODY FAT DETERMINED BY DIRECT AND D20 METHODSa Group Item 1 2 3 4 Actual ' empty body fat, % 15.09a 19.52a 24.58a 27.12a SE .33 .85 .95 .49 D20 1 pool Eggfy%b0dy 10.96” 15.35” 22.56a 24.64a SE 1.18 1.59 1.98 1.84 D20 2 pOOl gggfy%b0dy 9.16” 13.37” 17.24” 23.76” SE .81 1.19 1.79 1.22 a Means in a column with different superscripts differ (P<.05). 116 In Table 2-7, percentage empty body mineral (EBM) was underestimated (P>.05) to a greater extent using the 1CM method than the 2CM. EBM was underestimated using the 1CM method by 10.4, 3.7, 7.0 and 7.3% for each group, respectivly. EBM predicted using the 2CM method was underestimated in G1 by 6.0%, overestimated in G2 and G3 by 1.2 and .2%, respectively and underestimated by 4.3% in G4. Table 2-8 contains the actual weight and percentage of gut fill predicted by the 2CM method. Although not statistically significant, percentage gut fill differed from actual percentage fill by -14.5, +3.5, -3.5 and +20.7% for the respective groups. Quantity of fill (kg) differed by -22.1, —6.9, -12.3 and +9.9% for G1 to G4, respectively. While the magnitude Of difference from actual percentage and weight of gut fill appears to be great, the difference in water associated with gut fill does not completely account for the overestimation in EBHZO. Table 2-9 contains the means and standard errors for the actual weight of skeletal muscle (SKM) from the EB, percentage muscle Of the EB, protein content Of the EB skeletal muscle and percentage EBP originating from skeletal muscle. Skeletal muscle mass increased (P<.001) between each group, however, percentage SKM Of the EB decreased (P<.05) from G1 to G3 but did not differ (P>.10) between G3 and G4. SKM protein content, while numerically decreasing slightly, did not differ (P>.10) from G1 to G4, 117 TABLE 2—7. GROUP MEANS AND STANDARD ERRORS FOR PERCENTAGE AND WEIGHT OF EMPTY BODY MINERAL DETERMINED BY DIRECT AND 020 METHODSa Group Item 1 2 3 4 Actual empty body mineral, % 4.81a 4.30a 4.15a 4.00a SE .16 .12 .11 .12 DZO 1 pool empty body mineral, % 4.31a 4.14a 3.86a 3.71a SE .05 .06 .08 .03 D20 2 pool empty body mineral, % 4.57a 4.35a 4.16a 3.83a SE .04 .06 .09 .06 a Means in a column with different superscripts differ (P<.05). W 118 TABLE 2-8. ACTUAL AND PREDICTED WEIGHT AND PERCENTAGE GUT FILL FROM DISSECTION AND D20 DILUTION TECHNIQUESa Group Item 1 2 3 4 Actual GI fill, kg 33.51a 39.34a 48.24a 43.85a SE 1.13 3.03 2.28 3.93 D20 2 pool GI fill,kg 26.11a 36.63a 42.32a 48.19a SE 3.93 3.24 5.30 3.21 Actual GI fill, % 10.91a 9.87a 9.88a 7.84a SE .41 .69 .47 .69 D20 2 pool GI fill, % 9.33a 10.18a 9.53a 9.46a SE 1.45 .98 1.27 .70 ‘8 Means in a row with the same superscripts do not differ (P>.05). w 119 TABLE 2-9. GROUP MEANS AND STANDARD ERRORS FOR ACTUAL EMPTY BODY SKELETAL MUSCLE TRAITS USED WITH D20 PROCEDURES TO ESTIMATE SKELETAL MUSCLE Group Item 1 2 3 4 Actual empty body skeletal muscle, kg 126.25 156.95 182.68 214.97 SE 3.72 .58 2.81 2.69 Skeletal muscle protein, % 21.4 21.20 20.80 20.88 SE .24 .20 .14 .20 Actual protein from total skeletal muscle, kg 27.06 33.27 38.00 44.88 SE 1.09 .30 .61 .61 Actual percentage of EB protein from skeletal muscle, % 52.00 51.4 51.41 52.9 SE 1.27 .61 .44 .13 Percentage muscle of EB WT,% 46.09 43.79 41.51 41.75 SE .56 .44 .54 .68 120 averaging 21.0% for all animals. Quantity of protein (kg) in SKM increased with each group, however, the ratio of SKM protein to EBP did not differ (P>.10) between slaughter groups averaging 52% across all animals and groups. Since this relationship remains constant over the period Of time in which an animal is rapidly developing and fattening it can be useful in predicting skeletal muscle protein and ultimately SKM. Table 2-10 contains the regression equations developed from the data collected from the steers in this study to estimate EBHZO, EBFAT, SKM protein, EB LBM and EBP. In equation 1, 92% Of the variation in EBHZO was accounted for by the 020 pool A, suggesting that reasonably accurate determinations of EBHZO can be Obtained by using a 1CM method. Equation 2 and 3 estimate EBFAT (%:kg) from EBHZO (%:kg) which accounts for 99% and 91% of the variation in EBFAT, respectively. Predicting EBFAT by regression equation appears to be more accurate than estimating EBFAT by differences since errors in each method compound the problems and will reduce the accuracy Of estimation of EBFAT. Equations 4, 5 and 6 appear tO be useful in predicting the weight Of SKM protein, explaining 97, 98 and 87% Of the variation in skeletal muscle protein by using the relationships between EBHZO, EBP and D20 pool A and SKM protein. Equations 7 and 8 predict skeletal muscle quantity (kg) in the EB from EBHZO and EBP, respectively, «an. 4 ON: mm H tampons mm oa m6. \ on mm H mmmE Soon coma mm m om.m mm. mos.~ H.6Hn Acre mmm or .OHomsfi prmamxm w o.m mm. flow. mm.mau Roxy Ommmm or .OHOMDE Hmpmaoxm s Hm.~ 6w. 668d. one.m- 4 Soon can as .sflouono odomSE Hmpmamxm m oo.H mm. mam. 606.6: More one or .cflmuono fl THOMSE Hmpwfimxm m l mH.H so. Nee. HH.~I Roxy cummm ox .ceououo THOMSE ngmamxm e mm.HH am. New. m6.6ael Rose Ommmm ox .eammm m me. am. ~6m.Hu mm.mm Awe onmm m .eammm m oo.HH mm. Rom. mm.Hmn 4 Hood can or .onmm H unmanamuooo oaomaum> mannaum> a 0mm Mm COflmmmnowm DQOOMOPCH HCOUCOQOUCH ucmocwmmo Gem AAHh EDD 024 84% Nflom NBQEW ZHMBOMQ HAOmDS Adfimdmmm CMHB<3 woom NBQZM BUHDWMQ OB mZOHB.1). Calculations to determine the weight Of protein associated. with the skeletal muscle and subsequent determinations of the percentage of EBP from skeletal muscle are similar to those Of Haecker (1920) and Moulton (1922a,b). Protein determined in these earlier studies was determined from "flesh" as described previously. Since protein associated with fat was included in their calculations, removal of "fat. associated.jproteinfl ‘would reduce 'their ‘values. Of 'the %EBP (58%0 from SKM: tO be similar to those in the present study. Haecker’s study showed a narrow range for the percentage EBP from carcass flesh for the cattle that ranged in weight from 318 to 454 kg, which closely resembles the composition of the steers in the present study. While the percentage of EBP from skeletal muscle was decreased slightly in G2 and GB in this study, it was likely due to individual animal variation. One animal in G1 was slightly above average in muscling (compared to others in G1) thus increasing muscle protein and one steer in each Of 62 and G3 was slightly below average in muscle, thus causing lower muscle protein. Regardless, the values for EBP from SKM derived from cattle in this study, are similar to those derived from published data. The relationships can ultimately be useful in 130 predicting skeletal muscle mass as long as EBHZO can be accurately determined. SUMMARY Skeletal muscle ppotein. As the steers grew, the percentage Of skeletal muscle protein Of the empty body protein remained constant at about 52%. Percentage protein in the skeletal muscle, while becoming slightly diluted due to fattening (intramuscular fat), remained relatively constant at 21% across groups. These data suggest that skeletal muscle protein can be predicted if empty body protein can be accurately estimated or directly determined. Empty body water relationships. Empty body water as a percentage of lean body mass remained constant at 72.0% across all groups. Furthermore, the relationship of empty body protein to empty body water remained constant at .312. These data suggest that empty body protein and lean empty body mass can be predicted if empty body water can be accurately estimated. Dilution technigues. Equations from the one compartment dilution technique consistently overestimated empty body weight. The one compartment method showed a developmental change in accuracy of estimating empty body weight, overestimating empty body weight in lean animals and more accurately estimating empty body weight as the steers fattened. The two compartment equations overpredicted empty body weight in young, lean steers but 131 132 underpredicted EBWT in the final weight group. Epedigtion g: empty ppgy ghemicai gompopents. Both methods overestimated empty body water and thus empty body protein which is calculated from empty body water. The one compartment method equations more closely predicted empty body water in the leaner animals. These data suggest that equations used in this study do not adequately estimate empty body water and thus should not be utilized alone to accurately estimate empty body protein and in turn skeletal muscle especially in large frame, lean crossbred cattle. Furthermore, refinements and modifications of existing prediction equations and dilution principles are needed to account for the developmental Changes in empty body water, fat and protein relationships, in order to more accurately estimate empty body composition of cattle. Chapter 3 Estimation of Lean Body Mass, Empty Body Protein and Skeletal Muscle Protein from Urinary Creatinine Excretion in Continental European Crossbred Steers 133 ABSTRACT The relationship of urinary creatinine excretion (UCE) with lean body mass (LBM), empty body protein (EBP) and skeletal muscle protein (SMP) was studied. Genetically similar crossbred steers (Simmental X Angus X Charolais) were randomly allotted (5 per group) to one of four final slaughter groups (300, 390, 480 and 560 kg, respectively). Six days prior to slaughter, steers were acclimated to collection crates and total urine collected each day for 3 d. Individual day urine collections were measured, subsampled, pooled and analyzed for UCE at the termination of the collection period. Steers were slaughtered 2 d later with complete physical and chemical analysis conducted on all empty body components. Mean daily UCE (g/d) per slaughter group were 7.83, 11.42, 12.29 and 13.42, respectively. UCE was highly correlated to weight Of LBM, EBP and SMP (r=.92, .90 and .87, respectively). Equations predicting LBM, EBP and SMP were derived using stepwise regression procedures. Equations predicting LBM, EBP and SMP from UCE had R2 and RSD values of .84, .81, .75: 22.19, 5.46, 3.43, respectively. .Accuracy of prediction equations was greatly improved with the addition of fasted live weight (LW) into each equation. Prediction equations for LBM, EBP and SMP follow: 134 135 LBM = 59.37 + 4.915 x UCE (g/d) + .445 x LW (kg) EBP = 13.261 + .814 x UCE (g/d) + .1078 x Lw (kg) SMP = 6.338 + .161 x UCE (g/d) + .0642 x LW (kg) These data suggest that UCE may be useful as a research tool for estimating developmental changes in LBM, EBP and SMP in beef steers. INTRODUCTION Waterlow (1969) referred to the urinary metabolite of creatine phosphate, creatinine, as a valid global index of muscle mass. Past research data support this claim in humans, beef cattle and sheep, however, very little recent information is available which has quantified the relationship between urinary creatinine excretion and lean body mass in steers. Folin (1905) stimulated early interest in creatinine excretion during studies in which he found no change in the creatinine excretion from an individual receiving a meat - free diet. Brody (1945), Dinning et al. (1949), Lofgreen and Garrett (1954) and Van Niekerk et al. (1963a) each accumulated data from studies in beef cattle and sheep which showed high correlations (r > .65) between creatinine excretion and lean body mass. However, these researchers did not totally dissect the carcass and quantify the lean body mass. Recently McCarthy (1981), Benner (1983), Golpinath and Kitts (1984) and Hayden (1987) reported creatinine excretion increased. as live ‘weight increased indicating muscle mass was increasing. Each of these studies attempted to use creatinine excretion as a tool to assess the effects Of exogenous growth promoting agents and changes in frame size on muscle mass in beef. 136 137 In the present study, the Objective was twofold. 1) investigate the relationship between developmental changes in daily creatinine excretion and empty body composition. Secondly, develop equations which can be utilized to predict lean body mass, empty body protein and skeletal muscle protein and other live measurements in steers from daily creatinine excretion. METHODS Urine W Urine was collected by placing steers in individual 85 x 142 cm collection crates. Steers were placed into the collection crates 1-2 d before actual collection in order to allow them to acclimate tO the restraining chute and collection crates. Total urine was collected for 3 d from a 66 x 66 cm plexiglass collector under the collection crate. During the collection process, the urine passed through 2 layers of fine mesh steel screening and 2 layers of cheese cloth before entering the collector to minimize fecal and hair contamination. Urine was collected in 20 liter plastic containers to which 4 N H2804 was added to lower the pH Of the urine to 2-3. The containers were emptied daily and total volumes recorded. A 10% aliquot was Obtained each day, passed through 3 layers of Cheese cloth and stored at 2° C until the 3 d collection was completed. The 3 aliquots were composited and frozen at -20°C. Approximately 100 ml Of composited urine were filtered and analyzed. Mining, W Creatinine concentrations were determined in urine samples by a colormetric procedure (Sigma Chemical CO., 1978). W]. W Group means, standard errors of creatinine excretion, total urine excretion, lean body 138 139 mass, empty body protein and skeletal muscle protein were determined. Analysis of variance was conducted on all variables between slaughter groups. Fmediction equations were developed using stepwise multiple regression procedures. All analyses were conducted according to SPSS Base Manual (1989). RESULTS AND DISCUSSION Mean values for urinary creatinine excretion (mg/d), creatinine per kilogram live body weight (Cr/WT) and total urine output (TUR) for each group are presented in Table 3- 1. As expected, urinary creatinine excretion (UCE) increased with increasing live weight. ‘UCE significantly increased (P<.001) from G1 to G2 and G3. However, while UCE increased (P>.1) from GZ to G3, large variations in individual animal outputs were noted. Such variations are consistent with data from humans, rats and sheep (Forbes and Bruining, 1976). As expected, UCE was significantly higher in G4 than all other groups. Forbes and Bruining (1976) demonstrated the usefulness Of using UCE as an index of LBM as long as care is taken in collecting samples. In this study, urine output varied as much as 4 liters from day to day, however, UCE concentration also varied accordingly. Scrimshaw et al. (1966) reported that among other things, stress and strenuous excerise can each introduce a 5 to 10% variation in daily creatinine excretion. Paterson (1967) and Zorab et al. (1969) have demonstrated that daily UCE can vary and they stressed the importance of collecting several days urine output in order to accurately assess UCE. After examining available UCE data in cattle and sheep, these and 140 141 Table 3-1. GROUP AVERAGE DAILY URINE OUTPUT, URINARY EXCRETION OF CREATININE AND CREATININE PER KILOGRAM BODY WEIGHT IN CATTLE OVER TIME Group Item 1 2 3 4 No. of Animals 5 5 5 5 Average creatinine excretion, mg/day 7827.6a 11423.5” 12292.2” 13399.2C SE 332.0 212.0 393.8 582.2 Average daily creatinine excretion per unit of body weight, mg/kg 26.36” 29.22a 25.47” 24.71” SE 1.13 .48 .84 1.04 Average daily urine output, ml 3341.1 4539.1 6314.7 3684.0 SE 761.5 1262.0 1667.2 172.0 aMeans in the same row with different superscripts giffer (P<.01). ,c Means in the same row with different superscripts differ (P<.05). 142 other factors most likely are also applicable to livestock. Thus, potentially relatively large errors (5 to 20%) or larger are possible if one would rely strictly on a single day's UCE or single point UCE to predict lean body mass. Researchers in several recent studies each collected urine in cattle and determined daily UCE. They referred tO increasing UCE as an indicator Of differences in muscle mass or an index Of increasing muscle mass. McCarthy (1981) reported significant differences in UCE between small and large frame beef steers Of 6352 to 8705 mg/d and 6732.5 to 11982 mg/d, respectively. UCE values for comparable live weight, large frame steers in McCarthy's study were similar to steers of similar live weight, composition and UCE values in the present study. TUR and Cr/WT values in this study were similar to those reported by McCarthy (1981) and Hayden (1987) in steers Of similar weights. Gopinath and Kitts (1984) investigated muscle protein metabolism and UCE in Hereford steers with a beginning weight Of approximately 380 kg. After 24 d and approximately 33.6 kg gain, they reported similar UCE values (11,460 mg/d) to 62 steers in the present study. Throughout the duration of their study at collection days 56 and 63 (live wt Of approximately 450 to 465 kg), UCE values were similar to G3 steer UCE values in the present study. 143 Benner (1983) and Hayden (1987) each investigated the effects of trenbolone acetate and estrogenic implants on muscle protein metabolism and changes in body composition in continental European crossbred heifers (Benner) and steers (Hayden). These researchers reported increasing UCE values with increasing live weight and also higher UCE values for implanted animals. They concluded that increased UCE values Of implanted animals indicated increased muscle mass. Each supported their findings using either deuterium oxide or urea space dilution, estimating that the treated animals contained more empty body protein and thus more Skeletal muscle protein than controls. Table 3-2 contains values for weight Of lean body mass (LBM), weight Of fat-free muscle (FFM), percentage FFM Of LBM, weight of empty body protein (EBP) and weight Of skeletal muscle protein (SMP) for each group. Weight of LBM, FFM, EBP and SMP each increased from G1 to G4. However, percentage FFM Of LBM remained relatively constant at about 53.5%. This supports the finding of Forbes and Bruining (1976) in which they concluded that fat-free muscle comprised about one-half of the lean body mass in humans. Knowledge Of LBM, the percentage Of FFM of LBM and the ability to predict each is useful in measuring rates Of protein turnover i.e., synthesis and degradation studies in cattle. 144 TABLE 3-2. ACTUAL AVERAGE LEAN BODY MASS, FAT FREE MUSCLE, PERCENTAGE FFM OF LBM, EMPTY BODY PROTEIN AND SKELETAL MUSCLE PROTEIN IN GROUPS OF STEERS Group Item 1 2 3 4 No. of Animals 5 5 5 5 Actual lean body mass, kg 232.0 288.2 329.6 374.7 SE 3.87 2.31 4.22 4.58 Fat free muscle mass, kg 124.13 153.06 174.66 205.25 SE 3.62 0.66 2.87 3.14 Percentage FFM of LBM, % 53.53” 53.1” 53.0” 54.8a SE 0 74 0 25 O 40 0 25 Empty body protein, kg 52.0 64.8 73.9 84.8 SE 1.01 0 54 0.88 1.04 Skeletal muscle protein, kg 27.1 33.3 38.0 44.9 SE 1.09 .30 .61 .61 3° Values within a row with the same superscript differ (P <.05)- 145 Table 3-3 contains regression eqautions which predict LBM for steers in this study using UCE and other easily obtainable live animal traits. UCE (R2 = .84: eqn #1) was useful in predicting LBM. However, since live weight (LWT: kg) and 12th rib fat (12FT: cm) are highly related to body composition, equation #2 which includes UCE and LWT, accounted for 98% of the variation in LBM and dramatically reduced the residual standard deviation (RSD), from 22.2 to 6.6 kg. Equation #3 which included UCE, LWT and 12FT also accounted for 99% of the variation in LBM and only slightly improved the RSD (6.2 vs 6.6). A fourth equation which included only LWT and 12FH was also useful, but slightly less accurate, in predicting LBM (R2 = .98: RSD = 7.3). The high R2 and low RSD indicate these measurements allow for relatively easy determination Of LBM with or without using UCE as an independent variable. From the standpoint of predicting LBM from UCE and with as few number of other easily Obtained independent variables as possible, use Of UCE and LWT require the least amount of time and equipment necessary. Inclusion Of 12FT marginally improved the estimation Of LBM. However, accurate 12th rib backfat measurements must be Obtained by ultrasound which would necessitate a trained operator and thus an increase in labor and expense. 146 HH.em . Asoc unprepasu use has some + Ham.6 mm. eoems. eso.om Roxy usosm3 m>eu e ooo.mm : Asoc mmoGROAED poo has some + whom. Aexv unmfiw3 O>HH + om.o mm. mm.m Hoem.mm Ao\oc omumwoxm wcscsumono m Homvo. onv pooflm3 0>HH + mmo.o mm. mam.e oosm.mm Ao\oc oououoxm masseumouo m ma.m~ em. mm.am oomm.oo xo\oc ooumnoxm opacaummno H pcmaofimumoo moanmflwo> MODES: 0mm Nm cosmmmwmmm HQOOHODGH usmozomODCH coaumsom muss soon zsmu so emOHms GOHommo oe monesoom onmmmmomm .mam mamas 147 Table 3-4 contains equations which predict weight of EBP in steers from this study. As with equations predicting LBM, equation #5, using only UCE was useful (R2 = .81, RSD = 5.455) in estimating EBP. However, as previously mentioned, addition Of LWT and (or) 12FT as independent variables into equations with UCE increased R2 to .98 and significantly reduced the RSD, improving the ability Of equation #6 and #7 to accurately estimate EBP. Equation #8 also adequately estimated EBP without the need to analyze urine for creatinine content. Table 3-5 contains equations which predict weight of skeletal muscle protein. Equation # 9 using UCE as the sole indepedent variable in predicting weight of SKP had a coefficient Of determination (R2) of only .76 and RSD Of 3.43. Addition of LWT to equation #10 again greatly improved the ability to estimate SMP (R2 = .95, RSD = 1.6). Inclusion of 12FT into equation #11 marginally improved the ability to predict SMP (R2 = .96, RSD = 1.56), as did the elimination of UCE as an independent variable in equation #12 (R2 = .95, RSD = 1.51). Elimination of UCE as a variable related to muscle mass, may however, sufficiently bias the estimation of SMP, if an animal's actual weight is considerably exaggerated due to excessive fill. Table 3-6 contains the summary of significant differences using the Student’s T-Test comparing results of actual group values for LBM, EBP and SMP versus predicted 148 mmo.man Laue mnmsxoesu you new suwa + m~6.H mm. mass. moao.e “use pecans m>aq m mmoa.aal AEOV mmwsxofinu you new spud + mama. Roxy panama o>HH + moo.a mm. eon. mamm.e onoc omuouoxm mseceummwo 6 uses. Roxy prawns 0>AH + H68.H an. «as. mHo~.mH xo\ov oououoxo weesAuHOMO o mme.m Hm. oam.e Heeo.na xo\ov omuouoxo unassumono m usmflOwuumoo moanmwwm> Hones: omm Mm GOfimmmuomm umooumucH usmocwdwch cowumsom ZHmBONQ >D0m NBQEN b0 BEOHW3 BOHQmmm OB mZOHfifibom ZOHmmmmUmm .vln qu<8 149 omn.ou Asov mnocxoasu use new sums + mam.e no. case. Hmm.s Roxy panama m>su we oav.ou xsoc mumsxoasu use new sums + mmomo. onv panama o>HH + mmm.a mm. . eoao.» mmme.s xo\mc omumnoxm osncepmono as oaeoo. Amxv pnmflm3 o>flH + smm.a mm. Hoe. vmmm.o Ao\mv oouonoxo ocecepmono ca me.m m6. o.~ Noom.o xo\oc ooumnoxo msecflumono a ucmfiofimmooo moanoflum> Hones: 0mm Mm coammmuoom ummoumucH psmocmmoosH :OHuosom ZHmfiomm MQUmDZ AdBHAHXm m0 BmUHMB BOHQHMQ OB mZOHB.85, P<.001) for all steers suggesting that refinement Of prediction equations is needed to utilize these prediction methods with lean, large frame cattle today. 154 INTRODUCTION The most accurate determination of carcass composition as stated by Powell and Huffman (1968) is the complete chemical analysis Of the entire carcass. However, budgetary constraints, time, labor expenses and the loss Of carcass value limit the use of this procedure. Therefore, researchers are forced. to 'rely on convenient, indirect methods and procedures to Obtain reliable composition information at reasonable cost. Numerous methods to indirectly estimate carcass chemical composition Of cattle have been suggested (Hankins and Howe, 1946; Kraybill et al., 1952; Yeates, 1965: Garrett and Hinman, 1969: Ledger et al., 1973; Miller et al., 1988). Since carcass composition is the index for many research treatment comparisons, highly correlated estimation methods are essential tO give meaningful treatment results. deay, the most commonly used methods of estimating carcass chemical composition is that introduced by Hankins and Howe (1946) which uses the composition of the 9-10-11 rib section to predict the composition of the entire carcass. Specific gravity as first discussed by Kraybill et al., (1952) and later reviewed by Pearson et al., (1968), Garrett and Hinman (1969), has also been used as a predictor of carcass 155 . «.\I!:‘:'I\l..’u3 .. ..1.‘ I .8: I60. 1 |..w.!. 156 composition with both favorable (Garrett and Hinman, 1969: Ledger et al., 1973) and unfavorable results (Powell and Huffman, 1968; Lunt et al., 1985a: Jones and Rompala, 1985a: Miller et al., 1988). Fat thickness over the longissimus muscle at the 12 - 13 rib interface also has been examined and found to be highly correlated to the chemical composition of the carcass (Crouse and Dikeman, 1974). Development of the aforementioned methods to predict carcass composition was conducted using predominantly domestic-bred cattle notably Angus, Hereford, Shorthorn, Brahman or crosses of each” lThe biological and developmental nature of these breeds, when fed normal ad libitum diets, predisposes them to the accumulation of large quantities Of subcutaneous adipose tissue at market weights as indicated by Haecker, 1920: Trowbridge, 1922a,b: Callow, 1962 and thoroughly discussed by Berg and Butterfield, 1976. Interestingly however, Cole, Ramsey and Epley (1962) tested the equations of Hankins and Howe for predicting separable components (fat, lean and bone) in cattle of British, dairy and Zebu genetic background and they found them to be accurate predictors. The interest and increasing emphasis (n1 lean beef production has been a driving force behind research efforts to produCe less fat and more muscle in carcasses of domestic breeds of cattle. The introduction of continental 157 European breeds has proven to be genetically a much faster, easier method in which to significantly alter carcass composition of beef produced today than by altering the domestic breeds. Numerous research papers have documented the findings that continental European crossbred cattle produce leaner carcasses than domestic breeds of cattle. Recent studies by Charles et al. (1976a), Jones et al. (1982,1985b,c) and Shanin et al. (1985a,b,c) have shown that both the amount and distibution Of fat in the carcasses of continental European bred cattle differs from that of British breeds. Today’s crossbred cattle marketed at 13 tO 16 mo Of age typically have larger, heavier carcasses and less subcutaneous fat. These studies suggest that the established equations which estimate carcass composition by 9-10-11 rib section, specific gravity and fat thickness, may be less reliable in leaner carcasses from today’s feedlot cattle. Since cattle frame ~ types have changed since the time when estimating equations were developed, the present study was designed to evaluate the application Of existing prediction equations to carcasses from continental European crossbred animals at four developmental stages and body weights. Relationships between the prediction Of percentage Of carcass water, ether extractable lipid and protein using the composition and SG of the RIB and SG Of 158 the carcass were compared with actual carcass composition to determine usefulness Of these equations in cattle Of very uniform composition within each group as well as the diverse carcass composition between weight groups. New equations were generated if present equations proved to be inadequate. Furthermore, the relationships between the specific gravity Of the 9-10-11 rib section and specific gravity Of the carcass without kidney and pelvic fat and carcass composition also were examined. MATERIALS AND METHODS Expezimengal Animglgy Twenty, genetically similar, large framed (frame score 5 to 6), Simmental x Charolais x Angus crossbred beef steers previously described in Chapter 1 were used in this study comparing predicted carcass compostion with the actual chemical composition Of the carcass. The chemical composition Of the entire right side Of the carcass was determined by the procedures outlined in chapter 1. The left side Of each carcass was weighed, shrouded and chilled for a minimum Of 24 h. Left sides were ribbed, fat measurements taken at the 12-13 rib interface (to the nearest .01 mm), ribeye areas measured and USDA grades Obtained by trained MSU personnel. Each side was quartered with each quarter weighed in air to the nearest .05 kg on a platform scale. Each quarter was then immediately suspended in 4 C water and the weight (to the nearest gram) recorded, after any trapped air was removed from the carcass and kidney fat area. Specific gravity of the left side (SG) was determined by dividing the total of the forequarter and hindquarter weights by the difference between weight in air and the weight in water (Garrett and Hinman, 1969). Carcasses were allowed to drip for 5 min during which time the kidney and pelvic fat (KP) was removed and weighed. The hindquarter was then reweighed in 159 160 water without kidney and pelvic fat (8G2). This was done to reduce any variation in the amount Of trapped air in and around the KP on specific gravity and the resulting predicted carcass composition. Prediction Of carcass composition components was obtained from the equations Of Garrett and Hinman (1969) found in Appendix Table 4. The 9-10-11 rib section (RIB) was removed by the procedures described by Hankins and Howe (1946). The rib section was separated into soft tissues and bone with weights recorded and adjustments made for water loss. Soft tissues were ground three times through a 3 mm plate and subsampled. The samples were powdered and moisture, ether extractable lipid (EEL) and protein were determined by AOAC methods (AOAC, 1980). T-test comparisons were conducted between actual carcass composition and 9-10-11 rib estimated carcass composition using the equations reported by Hankins and Howe (1946) for steer carcasses, and those reported by Crouse and Dikeman (1974) and Miller et al. (1988). A complete list Of equations developed by Hankins and Howe (1946), Crouse and Dikeman (1974) and Miller et al., (1988) can be found in Appendix Table 13. Prior to dissection Of the rib section, the specific gravity Of the rib (SGR) was determined in the same manner as described for carcasses. Statistical analyses. Means and standard errors Of actual carcass composition and predicted composition were 161 calculated for each group Of five carcasses. Analysis Of variance was used to analyze differences between weight groups and the influence Of development on carcass components. Stepwise linear multiple regression procedures were used to develop equations to predict carcass composition. All statistical analysis were conducted using the Statistical Package for the Social Sciences (SPSS, 1989). RESULTS AND DISCUSSION Group means and standard errors of the carcass and 9- 10-11 rib section (RIB) chemical composition are presented in Table 4-1. Specific gravity means and standard errors for the left side of carcasses and the RIB of each group are also presented in Table 4-1. Additionally, the overall means and standard errors Of the chemical composition of the carcass and RIB Of all animals as one group is displayed in Table 4-1. The composition Of the carcasses and RIB within each group from this study were well within the range Of the carcasses and rib sections sampled by Hankins and Howe (1946). Carcass moisture from the overall group however, was 2.6% (absolute percentage points) higher than that of the Hankins and Howe (1946) study and 8.1% higher than the mean carcass moisture in the study by Crouse and Dikeman (1974). Overall carcass fat was 2.4 and 9.9 percentage points lower than the Hankins and Howe (1946) and Crouse and Dikeman (1974) studies, respectivelyu Similar values were true for the RIB with moisture being 1.0 and 12.0 percentage points, higher than reported in the Hankins and Howe (1946) and Crouse and Dikeman (1974) studies, respectively. RIB fat was 7.2 and 15.2% lower in the present study than the RIB fat reported in the earlier 162 163 studies mentioned. Interestingly, overall group mean carcass protein did not differ between the present study and the work reported by Hankins and Howe (1946) but was 1.75% higher than in the study Of Crouse and Dikeman (1974). The decrease in fat and increase in moisture is not surprising since during the past 10 - 15 yr there has been an effort to reduce fat in beef carcasses by selection, nutrition and use Of cattle from continental European genetic lines in this country. Table 4-2 contains the actual and predicted group means and standard errors for percentage carcass moisture. Predicted carcass moisture was derived using the equations Of Hankins and Howe (1946) and Crouse and Dikeman (1974) found in Appendix Table 4. AS seen in Table 4-2, both prediction methods overestimated carcass moisture (P<.05) in groups 1, 2 and 4, and while not statistically significant, also tended to overestimate carcass moisture in G 3. It is interesting to note that as the carcasses increased in fat content and decreased in moisture both equations tended to more accurately predict carcass moisture. When comparing methods Of predicting ether extractable lipid (EEL) of the carcass soft tissues in Table 4-3, EEL was underestimated (P<.01) in each group by the Hankins and Howe (1946) equation and also by the equation of Crouse and Dikeman ( 1974) in groups 1 and 2. Predicted carcass fat 164 TABLE 4-1. GROUP MEANS AND STANDARD ERRORS FOR CARCASS, 9-10-11 RIB COMPOSITION AND SPECIFIC GRAVITY Group Item 1 2 3 4 Overall Groups Carcass H O, % 63.93 59.53 ’54.8 52.64 57.72 58 .53 .77 .93 .68 1.06 Carcass EEL, % 16.87 23.18 29.28 32.01 25.34 SE .40 .96 1.16 .77 1.40 Carcass protein, % 18.11 16.46 15.11 14.51 16.05 SE .30 .18 .25 .19 .34 9-10-11 rib H O, % 66.96 61.27 53.24 50.6 58.02 SE . .58 .88 .36 .96 1.53 9-10-11 rib EEL, % 15.19 20.98 31.15 34.75 25.53 SE .39 .94 .38 1.4 1.84 9-10-11 protein, 17.47 17.14 14.94 14.17 15.93 SE .26 .10 .25 .36 .34 Carcass SG ' with KP 1.0747 1.0694 1.0585 1.0528 SE .0018 .0024 .0019 .0009 Carcass SG without KP 1.0828 1.0734 1.0638 1.0585 SE .002 .002 .002 .001 RIB SG 1.1116 1.085 1.0758 1.0664 SE .005 .0018 .0025 .0015 differ (P <.05). ‘ED Values within a column with different superscripts vaI.' 165 TABLE 4-2. COMPARISONS OF ACTUAL CARCASS MOISTURE WITH PREDICTED CARCASS MOISTURE Group Item 1 2 3 4 Actual H20, % 63.93a 59.53a 54.8a 52.64a SE .53 .77 .93 .68 Hankins/HoweC H O, % 67.05” 62.79” 56.76a 54.77” SE .43 .66 .27 .72 Crouse/Dikemand H O, % 65.18a 61.14a 55.44a 53.56” SE .41 .62 .26 .68 ab Values within a column with different superscripts c d differ (P <.05 or less). Equation from Hankins and Howe (1946). Equation from Crouse and Dikeman (1974). 166 tended (P>.10 or greater) to be lower in groups 3 and 4. Estimation of carcass fat by equations reported by Miller et a1. (1988) derived from fed (finished) steers (equation 1) and equation 2 from all types (calves, feeders, yearlings, fed steers and cows) overestimated (P<.05) carcass fat in group 1 but did not differ (P>.15) from actual carcass fat in groups 2, 3 and 4. The Miller equations when tested on other data sets in addition to this study may come to be widely accepted for predicting carcass fat. Table 4-4 contains the group means and standard errors Of the actual and estimated percentage carcass protein using the percentage protein in the RIB and the prediction equations Of Hankins and Howe (1946) and Crouse and Dikeman (1974). Both equations did not differ (P>.05) in predicting carcass protein from actual carcass protein in G 1. As the carcasses increased in fat and decreased in percentage protein the Hankins and Howe (1946) equation overestimated (P<.05) carcass protein. The equation developed by Crouse and Dikeman (1974) overestimated (P<.05) carcass protein in G 2 but did not differ (P>.15) from actual carcass protein in groups 3 and 4. The equation developed by Crouse and Dikeman (1974) while presently not widely used, appear to be valid for .he 170 predicting carcass protein in cattle with greater than 24% carcass fat. 167 Table 4—5 contains a summary of the student’s t-test statistical analysis using each equation and comparing the predicted composition to actual composition. As indicated in the footnotes Of each table, nonsignificance is indicated when P is greater or equal to .15. In several cases the reported P value approached significance. If more animals were included in the present study significant differences between the actual and predicted composition would be expected. Table 4-6 is a summary Of the differences in the means between actual and predicted carcass moisture, ether extractable lipid and protein. It is interesting to note that of all reported prediction equations used in the comparisons in the present study, no equation accurately predicted the carcass composition of the carcasses highest in moisture and protein and lowest in fat. It may be necessary to establish an accepted prediction equation for carcasses less than approximately 20% carcass fat or conduct total dissection and grinding in order to establish baseline carcass data if needed. As the basis for comparison in many research studies involving beef cattle, carcass composition must be easily and reliably obtained with carcass loss, labor and expenses kept to a reasonable cost. The results Of the present study indicate that although the 9-10-11 rib may be a widely accepted method of estimating carcass composition, it appears that enough 168 TABLE 4-3. COMPARISONS OF ACTUAL AND PREDICTED CARCASS ETHER EXTRACTABLE LIPIDa Group Item 1 2 3 4 Actual EEL, % 16.87” 23.18” 29.28” 32.01” SE .40 .96 1.16 .77 Hankins/Howed EEL, % 14.73” 19.02” 26.54” 29.23” SE .29 .70 .28 1.04 Dikemane EEL, % 15.58” 19.98” 27.70” 30.47” SE .29 .72 .29 .77 Miller 1f EEL, % 18.74” 22.79” 29.90” 32.45” SE .27 1.48 .60 .98 Miller 29 b EEL, % 19.12” 22.83 29.38” 31.66” SE .25 .61 .25 .90 abc Values within a column with different superscripts differ (P <.05 or less). d Equation from Hankins and Howe (1946). e Equation from Crouse and Dikeman (1974). f Equation from Miller et al. (1988), fed cattle only. g Equation from Miller et al. (1988), all cattle. 169 TABLE 4-4. COMPARISONS OF ACTUAL AND PREDICTED CARCASS PROTEIN Group Item 1 2 3 4 Actual Carcass Protein, % 18.11a 16.46a 15.11a 14.51a SE .30 .18 .25 .19 Hankins/Howe P, % 17.54a 17.33” 15.90” 15.40” SE .17 .07 .16 .23 Dikeman P, % 17.31a 17.06” 15.38a 14.80a SE .20 .08 .19 .27 5° Values within a column with different superscripts differ (P <.05). 170 TABLE 4-5. SUMMARY OF STUDENT’S T’TEST COMPARISONS BETWEEN ACTUAL AND PREDICTED CARCASS MOISTURE, FAT AND PROTEINa Group Item 1 2 3 4 NO. Of Animals 5 5 5 5 % Carcass H20 Hankins/Howe” .004 .011 .12 .003 Crouse/Dikeman” .08 .09 NS .04 % Carcass EEL Hankins/HOweb .003 .008 .05 .002 Crouse/Dékemanc .02 .02 NS .10 Miller 1 .005 NS NS NS Miller 28 .002 NS NS NS % Carcass Protein Hankins/Howe” NS .003 .01 .02 Crouse/Dikeman” .07 .009 NS NS Nonsignificance at P = .15 or greater. Equation from Hankins and Howe (1946). Equation from Crouse and Dikeman (1974). Equation from Miller et al. (1988), fed cattle only. Equation from Miller et al. (1988), all cattle. mQOUm 171 TABLE 4-6. SUMMARY OF ABSOLUTE DIFFERENCES BETWEEN ACTUAL AND PREDICTED CARCASS MOISTURE, FAT AND PROTEIN Group Item 1 2 3 4 % Carcass H20 Hankins/Howea 3.12 3.26 1.96 2.13 Crouse/Dikeman” 1.25 1.61 .64 .92 % Carcass EEL Hankins/Howea -2.14 -4.16 -2.74 -2.78 Crouse/Dikemanb -1.29 —3.20 -1.58 -1.54 Miller 1” 1.87 — .39 .62 .44 Miller 2d 2.25 - .35 .10 .35 % Carcass Protein Hankins/Howea — .57 .87 .79 .89 Crouse/Dikemanb - .80 .60 .27 .29 Equation from Hankins and Howe (1946). Equation from Crouse and Dikeman (1974). Equation from Miller et al. (1988), fed cattle only. Equation from Miller et al. (1988), all cattle. QOU‘m 172 change in the physical and compositional makeup of typical market. cattle: has occurred. which suggests that the equations reported by Hankins and Howe (1946) are not accurate enough for use today. Continued use of equations reported by Hankins and Howe (1946) overestimates the carcass protein and underestimates carcass fat to such an extent that incorrect and costly conclusions may be made. The more recent studies. by Crouse and Dikeman (1974) and Miller et al. (1988) have reported equations which were found to adequately estimate carcass fat and protein in steers which. had. in excess of 24% carcass fat in the present study. Further validation of either the previously mentioned equations or the equations derived from the present study using the 9-10-11 rib section needs to be more extensively studied. Tables 4-7, 4—8 and 4-9 contain the group means and standard errors of actual carcass composition and carcass composition predicted using the specific gravity Of each carcass and equations developed by Garrett and Hinman (1969). Specific gravity equations underpredicted (P<.05) carcass moisture in groups 1.2nul 2 and tended (P>.05) to slightly underpredict moisture in groups 3 and 4. Specific gravity estimated carcass fat in G 1 did not differ (P>.05) from actual, however, in groups 2, 3 and 4 carcass fat was underpredicted (P<.05) in all cases. Carcass protein in Table 4-9, was accurately predicted.iJ1(3 1 but 173 TABLE 4-7. COMPARISONS OF ACTUAL AND PREDICTED CARCASS MOISTURE USING SPECIFIC GRAVITY Group Item 1 2 3 4 Actual H20, % 63.93a 59.53a 54.8a 52.64a SE .53 .77 .93 .68 Garrett/Hinman H 0, % 59.42” 57.45” 53.36a 51.2a SE .67 .91 .71 .34 _4 ab Values within a column with differ (P <.05). different superscripts 174 TABLE 4-8. COMPARISONS OF ACTUAL AND PREDICTED CARCASS ETHER EXTRACTABLE LIPID USING SPECIFIC GRAVITY Group Item 1 2 3 4 Actual EEL, % 16.87a 23.18a 29.28a 32.01a SE _ .40 .96 1.16 .77 Garrett/Hinman ' EEL, % 17.80a 20.59” 26.39” 29.41” SE _ .95 1.29 1.0 .48 5° Values within a column with different superscripts differ (P <.01)- 175 TABLE 4-9. COMPARISONS OF ACTUAL AND PREDICTED CARCASS PROTEIN USING SPECIFIC GRAVITY Group Item 1 2 3 4 Actual Protein, % 18.11a 16.46a 15.11a 14.51a SE .30 .18 .25 .19 Garrett/Hinman Protein, % 18.27a 17.62” 16.26” 15.54” SE .22 .30 .24 .11 anValues within a column with differ (P <.05). different superscripts 176 was overestimated (P<.05) in groups 2, 3 and 4. These results are consistent with those of Powell and Huffman (1968), Lunt et al. (1985a), Jones and Rompala (1985) and Miller et al. (1988) all of which discouraged the use of specific gravity to estimate carcass fat. The results Of the present study however, are contrary to those reported by Waldman et al. (1969) and Gil et al. (1970) both of which reported that specific gravity was not accurate for carcasses with <20% fat. More research data for carcasses from the U.S. cattle population with < 20% carcass fat are needed in order to determine the most reliable method of determining composition. Specific gravity Of the carcass may continue to be a useful tool, contrary to the findings of Powell and Huffman (1968), Lunt et al. (1985b) and Miller et al. (1988). Researchers must realize however, that any method of handling which increases the chance of entrapping excess air under the fat layer (as is done in hide pulling) can render this method of estimating carcass composition useless. Careful thought and planning needs to accompany design of experiments utilizing specific gravity. Use Of specific gravity to estimate carcass composition should only be conducted on carcasses which have been skinned in the tradition cradle method. It is recommended that the equations developed by Garrett and Hinman (1969) not be used as the single estimate Of carcass composition since 177 biased, inaccurate results may be Obtained. The equations using carcass specific gravity with and without kidney and pelvic fat as derived in the present study, need to be validated with a different population of carcasses to further refine them. Regression equations in Table 4-10, predicting percent carcass moisture, ether extractable lipid and protein from the RIB composition Show that percentage chemical fat of the RIB accounted for a high proportion of the variation in carcass fat as indicated by an R2 of .93 and residual standard deviation (RSD) of 1.65. Additionally, percent moisture Of the RIB accounted for 91% Of the variation in carcass chemical moisture across all slaughter groups. Equation 3 (Table 4-10) was derived from all carcasses in the present study. It showed that 76% of the variation in carcass protein was accounted for by the percent protein in the RIB from groups 1 to 4. Results of the earlier analyses comparing various prediction equations showed that since carcass protein was accurately predicted by the Hankins and Howe (1946) equation, it may be possible to improve the ability Of the equation to estimate carcass protein by using only data from groups 2, 3 and 4. Equation 4 (Table 4—10) was derived from the percentage protein in the RIB from groups 2, 3 and 4. The R2 value was improved tO .82 and the RSD was decreased to .40, indicating that equation 4 did account for more Of the variation and reduce the 178 .SHGO e0 I No Bone omumHSOHwo o .Aeo I HOV mmsoum Ham Bone omuoasoaoo o mHm mo sawuoum w oe. mm. seem. emwm.m tampons w unmoumo e omHm mo cflmuoum w ms. 66. mmmmm. Hom.m seduced w nnnonmo m anm no 0mm 6 ee.s Hm. memo. mmm.ms 0mm 8 mmmonmo m bmHm MO Amm w mm.H mm. wmmn. voo.m Qmm w mmmOHOU H ucoflofimmmoo moHooHum> mauofluo> .0: 0mm Nu coflwmmummm ummouwucH ucmocmmoocH usmpcwmwo com ZHmeomm 02¢ QHmHA mqmdeoemexm mmmfim .mmDBmHOS mmmomflo mwdfizmommm BoHommm OB mZOHBdDOm onmmmmwmm .oalv mamdfi 179 standard. deviation of predicted carcass protein in carcasses from groups 2, 3 and 4. Table 4-11 contains regression equations predicting percent carcass moisture from the specific gravity of the carcass with and without the kidney and pelvic fat. As is evident in equations 5 and 7, removing the kidney and pelvic fat improved the ability (R2 = .83 vs .85) of specific gravity of the carcass to estimate carcass moisture. Addition Of hot carcass weight (HCWT) as well as specific gravity further improved both equations 6 and 8 (R2 = .88 and .89: RSD = 1.63 and 1.60, respectively). As with the use Of specific gravity to predict carcass moisture, Table 4—12 shows that removal Of kidney and pelvic fat from the carcass improved the ability to predict percent carcass fat (R2 = .84 and .86 for equations 9 and 11, respectively). Hot carcass weight as a second variable improved the equations even more as indicated by R2 values of .90 and RSD of 2.00 and 1.94, respectively for equations 10 and 12. Regression equations predicting percent carcass protein (Table 4-13) from carcass specific gravity accounted for less of the variation in carcass protein than equations previously discussed. This is not suprising since specific gravity is more highly associated with the degree Of fatness and water content. Regardless, carcass specific gravity with and without kidney fat accounted for 77 and 180 mmo.n 530m + om.H mm. o.vam mm.HoHI mM0\3 0m mmoouoo Omx w mmmonoo w em.e no. em.e~e 6.6mm: GMO\3 um Om: w mmmonoo mumOMmO s mmo.l B30: + «mo.e mm. os.mo~ ma.mmsn ox\3 om mucoumo Omm w mmouumu o mm.H mm. m¢.om¢ mv.amvl mM\3 mm ON: a wmmonou mmmouoo m usmflOeummoo mmaooeum> wanmeum> .0: 0mm Nm coflmmwumom uQOOHOuGH uGOOQOQOUCH ucmucommo com >BH> manoeuo> .0: 0mm Mm :Oflmmmuomm ummommch unmocmaoocH pcwocommo com VBH>¢mU UHmHOWmm mmdUMdU 20mm QHmHA mam¢eo4¢9xm MMZBN mm40m<0 mwdfizmommm BOHQHMA OB mZOHB manmwnm> .0: com um :OHmmmHmmm unmonoucH usmucmmoocH ucmocmmoo com mmdvmdo SOMh ZHWBOmm mmdomdo m04MU OHhHUmmm mZOHfidbom ZOHmwmmwmm .MHI¢ mumfla 184 mm.m m6. o.mom| mm.mmm Om mHm Amm w Ohmo om Hm. H6. 6H.mm mm.wml 0m mHm m w onto me m6N.N 66. mm.m~m mm.wwHI Om mHm Ommw tho ma mom.m 66. mmm.vmml mam.mmv Um mHm Ammw mHm 6H ucmfloflwuwoo mmauoewm> manwfluo> .Oc Qmm NM coflmmmumom pmoonmucH unmocmmoecH usmocwmmo com NBH>4mU UHhHUmmm mHm HHIOHIm 20mm DHmHA mqmfifiodmfixm mmmfim mHm Q24 ZHWBOMQ QZ< QHmHA mquEU .85: P<.05) to actual carcass moisture, EEL and protein. Prediction equations developed by Hankins and Howe (1946) consistently underpredicted (P<.05 or less) percentage carcass EEL by 2.1 to 4.1 percentage points. Prediction equations reported by Crouse and Dikeman (1974) also underpredicted carcass EEL by 1.3 to 3.2 percentage points. Predicted carcass EEL using equations reported by Miller et al., (1988) did not differ (P>.15) from actual carcass EEL. Carcass protein was overpredicted (P<.05) using the equations of Hankins and Howe (1946) in group 2, 3 and 4 steers and underpredicted carcass protein in G 1 (P>.15). Equations developed by Crouse and Dikeman (1974) to estimate carcass protein appear to be valid for predicting carcass protein in carcasses with greater than 24% fat. Although specific gravity of the carcass was highly correlated (r>.85) with carcass moisture, EEL and protein, the equations reported by Garrett and Hinman (1969) did not accurately predict carcass composition in carcasses with >20% fat in the present study. Results Of the present .he 185 186 189 .op study did however, suggest that carcass specific can be used to accurately predict carcass composition in carcasses with <20% fat using the equations Of Garrett anf Hinman (1969). Specific gravity of the carcass with the kidney fat removed was also highly correlated to carcass composition. It is concluded in the present study that enough of a change in the physical and compositional makeup Of typical market cattle has occurred to justify development and validation of refined equations using the 9-10-11 rib section and specific gravity from cattle typical Of the current U.S. cattle population. Chapter 5 Estimation of Beef Carcass Skeletal Muscle from 9-10-11 Rib Section of Continental European Crossbred Steers 187 ABSTRACT Growth Of carcass soft tissues (CST) and changes in the relationships involving distribution Of carcass moisture (CW), fat (CFAT) and protein (CP) in carcass muscle (CMUS) were examined in large frame (Simmental X Charolais X Angus) steers. Twenty steers, randomly allotted to one Of four groups (n=5/group), were slaughtered when fasted live weights were 300, 390, 480 and 560 kg for the four groups, i.e., G1, G2, G3 and G4, respectively. CW, CFAT and CP were directly determined by physical separation and chemical analysis. Carcasses were dissected into CST (CMUS and adipose tissue, AT) and bone (CB). CW was 63.9, 59.5, 54.8 and 52.6%, for G1 to G4, respectively. CFAT was 16.9, 23.2, 29.3 and 32.0%, for G1 to G4, respectively. CMUS comprised 66.0, 59.2, 59.2 and 57.9% of hot carcass weight, respectively, in each group. Protein (P) content Of the CMUS was not different (P>.10) between groups. Values ranged from 20.8 to 21.4%, with a mean Of 21% across all groups. Percentage CP in G1 to G4 was 18.0, 16.5, 15.1 and 14.5, respectively. Total CMUS P as a percentage of CP did not differ between groups (95.0, 95.0, 94.3, 95.2: P>.10), averaging 95%. Bone content Of the 9-10-11 rib section (RIB) was highly correlated (P<.001) to CB and can be used to predict CB. These data were used to develop multiple 188 189 regression equations to predict CST, weight and percentage Of CMUS in beef carcasses from this study. INTRODUCTION Simple and accurate estimation Of beef carcass composition by indirect methods continues to be a goal Of animal scientists“ Of current acceptable methods, Schroeder et al. (1987) and Miller et al. (1988) reported the 9-10-11 rib section method (RIB) described by Hankins and Howe (1946) to most accurately estimate carcass composition. Both studies, however, reported that although th RIB was the method Of choice in estimating carcass composition, as carcass fat increased in moderate to large frame steers the RIB became less accurate for predicting carcass fat and protein. Updated prediction equations have been generated which more accurately estimate carcass fat and protein. Selleck. and 'Fulloh (1968) and Berg and Butterfield (1976) recommended that fat, bone and edible product, (skeletal muscle) should be the endpoint by which changes in beef carcass composition should be measured. Present research efforts attempt to respond to the demand for lean meat products and high saleable yields by concentrating on decreasing carcass fat and increasing skeletal muscle by genetic improvements or treatment with exogenous growth promotants. Present prediction equations, however, do not appear to adequately recognize and measure the full 190 191 magnitude Of response Obtained through genetic selection and use of exogenous growth promoting agents. Increased emphasis on measuring lean tissue (i.e., muscle mass) in beef cattle necessitates development Of reliable research tools and prediction methods which can accurately and repeatably measure differences in skeletal muscle mass in beef carcasses. The present study was designed to evaluate developmental relationships and changes in carcass protein and bone, skeletal muscle protein as a percentage Of carcass protein, protein content of skeletal muscle and the composition Of the RIB for use in development Of prediction equations to estimate carcass skeletal muscle. MATERIALS AND METHODS Experimental animals. Twenty genetically similar Simmental X Charolais X Angus steers were randomly allotted to four slaughter groups as indicated in Table 5—1. All steers were fed ad libitum, a 13% crude protein corn silage — high moisture corn — soymeal concentrate diet during the growing phase (diet 1). After G 2 animals were slaughtered, the remaining steers (G 3 and G 4) were fed a 11 % crude protein corn Silage - high moisture corn and soy concentrate diet during the finishing phase. When each steer reached the designated weight, it was slaughtered according to commercial practices. Carcass Physical and Chemical Composition. Carcasses were split and the right Side of each carcass was physically' dissected. into individual soft 'tissues ‘which included: carcass skeletal muscle (CMUS), adipose tissues (AT) and. carcass bone (CB). All carcass tissues. were weighed and subsampled. Moisture, ether extractable lipid and protein (N x 6.25) were determined on each sample by AOAC methods. In order to Obtain left side tissue weights, the weight of soft tissues in the right side (minus kidney, pelvic and thoracic cavity (KPH) adipose tissue) as a percentage Of the right side, was multiplied by the weight of the left side (minus KPH). All weights were pooled to 192 III'" .I III. I| 1|! Ill 1.1. 1... ‘5 -nl '1 I I. ‘ .. ..‘b-I . 1||Drtf I. ..bllur'lugfa an .1“: I .. . 1’ I. u. .46.... . ......hqrnaaio... . . I. . 1 . 57... L 193 TABLE 5-1. EXPERIMENTAL ALLOTMENT OF STEERS INTO SLAUGHTER WEIGHT GROUPS Group 1 2 3 4 Number per group 5 5 5 5 Fasted live weight, kg 300 390 480 560 Age, mo 10 12 14 16 194 Obtain the physical and chemical composition Of each carcass. 9-10-11 Rib Section Composition. Rib sections were removed from the left side Of each carcass according to the methods described by Hankins and Howe (1946). Chemical analysis was performed on the soft tissues. Estimation Of carcass chemical composition and percentage carcass bone was made using equations reported by Hankins and Howe (1946) for steers found in Table 5—2. Statistical Analysis. Comparisons of estimated carcass composition using existing prediction equations with actual composition were reported in Chapter 4. Paired t-test analyses were used to evaluate differences between actual and.jpredicted.lcarcass composition. Stepwise linear regression procedures (SPSS/PC+ V2.0 Base Maual, 1989) were used to derive new prediction equations. Equations reported are those in which R2 and RSD were optimized. 195 TABLE 5-2. PREDICTION EQUATIONS DERIVED BY HANKINS AND HOWE (1946) TO ESTIMATE CARCASS PROTEIN AND BONE Carcass Protein: %CP = 6.19 + .65 x % P Of RIB R2 =.83 RSD = .79 Carcass Bone: %CB = 5.52 + .57 x % Bone in RIB R2 = .80 RSD II ...: N m RESULTS AND DISCUSSION Means and standard errors for actual carcass composition are presented in Table 5-3. The carcasses from the steers in the present study ranged in weight from 188.1 kg to 365.7 kg and had 12th rib fat measurements that ranged from 2.6 to 11.4 mm, typical Of the current cattle population in the [LSL Table 5-4 contains more detailed carcass dissection data including dissectible soft tissues which consists Of skeletal muscle and fat. As one would expect, the percentage Of soft tissues (CST) Of the hot carcass weight (HCWT) increased in each group from a low of 82.9 in G1 to 87.7% in G4, respectively, indicating that as the steers increased in both live and carcass weight the soft tissues of the carcass grew at a more rapid rate than bone, which as a: percentage decreased. Carcass skeletal muscle increased in absolute weight in each group, but, as expected the percentage Of the carcass skeletal muscle decreased to about 58% which is consistent with data in the literature. Table 5-5 contains the group means and standard errors of the chemical composition Of the hot carcass and the 9- 10-11 rib section (RIB) from the left sides of each carcass. Additionally, the percentage of bone in the carcass and the RIB is reported in Table 5-5 by group 196 TABLE 5-3. GROUP MEANS AND STANDARD ERRORS FOR CARCASS TRAITS Group Item 1 2 3 4 Hot carcass weight, kg 188.1 247.2 303.7 365.7 SE 3.8 1.84 2.74 3.12 12th rib fat, mm 2.6 4.8 8.7 11.4 SE .02 .03 .03 .05 Longissimus area, cm 60.3 75.2 80.8 86.6 SE .98 1.93 3.71 3.60 KP, % 2.0 2.5 2.5 3.1 SE .11 .16 16 .19 Yield grade 1.7 1.8 2.4 3.0 SE .12 .16 .13 .18 198 TABLE 5-4. GROUP MEANS AND STANDARD ERRORS FOR CARCASS TRAITS Group Item 1 2 3 4 Carcass soft tissues (CST), kg 156.0 209.9 262.9 320.7 SE 3.99 2.43 2.28 2.66 CST % of HCWT, 82.87 84.93 86.51 87.69 SE .57 .37 .36 .41 Carcass skeletal muscle, kg 124.2 154.5 179.7 211.7 SE 3.68 .46 2.76 2.72 Carcass muscle, % 66.0 62.51 59.19 57.89 SE .72 .52 1.0 .47 Carcass bone, % 17.1 15.1 13.4 12.3 SE .47 .44 18 .32 199 means. It is interesting to note that the decrease in percentage bone in the RIB is not as dramatic as the decrease in carcass bone as shown in Table 5-4. Table 5-6 contains the percentage protein (N X 6.25) found in the composite skeletal muscle. Though a slight nonsignificant (P>.10) numerical decrease Of protein occurred in successive groups, the average percentage protein for all steers was 21.0%, consistent with present USDA findings of 20.94% (USDA, 1987). Since detailed total physical dissection into skeletal muscle and carcass adipose tissue was conducted on each carcass, it was possible to determine both the total protein content (kg) Of the CST as well as the total protein content (kg) of only the skeletal muscle (Tables 5-4 and -5). The ratio Of skeketal muscle water to Skeletal muscle protein remained constant averaging 3.54. The ratio Of skeletal muscle protein (kg) to total carcass protein was determined to be constant averaging .95 across all groups. This relationship has not been reported in the literature. During normal development since the ratio Of water to protein in skeletal muscle remains constant as in the present study and the CST water to protein ration remained essentially constant at about 3.62 (Chapter 1), it follows that the relationship of skeletal muscle protein to carcass protein should remain constant. This relationship is important in studies in which the effects Of various exogenous anabolic compounds 200 on carcass composition and skeletal muscle mass are to be measured. In order tO measure the effects Of such compounds on muscle, either complete physical dissection must be conducted, or typically the RIB is used to predict carcass protein and fat, and then effects on carcass muscle are extrapolated from percentage carcass protein. Carcass muscle can be estimated only if equations accurately predict carcass protein and bone. Table 5-7 contains the group means, standard errors and statistical comparison (paired t-test) between actual percentage carcass bone, predicted percentage carcass bone from the equation of Hankins and Howe (1946) and predicted carcass bone using equation 1 in Table 5-8 derived from the present study. In G1 and GZ prediction Of percentage carcass bone using the Hankins and Howe equation (H/H) did not differ from actual carcass bone (P>.10). However, in G3 and G4 predicted percentage carcass bone (H/H) differed (P<.01) from actual. Table 5—8 contains equation 1 to predict percentage carcass bone using the percentage bone in the RIB as the independent variable. Percentage bone Of the RIB accounted for 76% of the variation in carcass bone across all groups and more accurately (P>.10) predicted percentage carcass bone in G3 and G4 (Table 5-7) than equations derived by Hankins and Howe (1946). Also included in Table 5-8 are equations 2 and 3 which estimate percentage carcass protein - 946' 201 TABLE 5-5. GROUP MEANS AND STANDARD ERRORS FOR CARCASS AND 9-10-11 RIB COMPOSITION Group Item 1 2 3 4 Carcass H20, % 63.93 59.53 54.8 52.64 SE .53 .77 .93 .68 Carcass EEL, % 16.87 23.18 29.28 32.01 SE .40 .96 1.16 .77 Carcass protein, % 18.11 16.46 15.11 14.51 SE .30 .18 .25 .19 9-10-11 rib H20, % 66.96 61.27 53.24 50.6 SE .58 .88 .36 .96 9-10-11 rib EEL, % 15.19 20.98 31.15 34.75 SE .39 .94 .38 1.4 9-10—11 protein, % 17.47 17.14 14.94 14.17 SE .26 .10 .25 .36 9—10-11 bone, % 19.63a 17.69” 17.23”” 15.79” SE .49 .46 .88 .40 “§°°° Values within a row with different superscripts differ (P <.05)- 202 TABLE 5-6. GROUP MEANS FOR PERCENTAGE PROTEIN IN SKELETAL MUSCLE AND PERCENTAGE OF SKELETAL MUSCLE PROTEIN IN TOTAL CARCASS PROTEIN Group Item 1 2 3 4 Skeletal muscle, protein, % 21.4 21.2 20.8 20.9 SE .12 .10 .24 .16 Skeletal muscle HZO/protein ratio 3.54 3.55 3.55 3.52 SE .03 .04 .03 .06 Carcass skeletal muscle protein of total carcass protein, % 95.0 95.0 94.3 95.2 SE .14 .12 .29 .13 203 from the protein content of the RIB as discussed in Chapter 4. Table 5-9 contains the flow chart and list Of required information to predict skeletal muscle using the RIB. Carcass soft tissues can be determined by subtracting the predicted carcass bone (kg) from hot carcass weight as in step 1. The quantity of carcass protein in CST is then predicted in step 2 using an equation which accurately predicts carcass protein from the RIB. Ninety five percent of the protein associated with skeletal muscle protein is determined in step 3. Weight of skeletal muscle can be predicted in step 4 by dividing skeletal muscle protein by .21. Table 5-10 contains an example using data from the present study tO estimate CST using the method outlined in Table 5-9. Table 5-11 contains actual and predicted carcass protein reported in Chapter 4. Multiplying the predicted CST by the estimated percentage protein in the carcass and then by .95 as indicated in Table 5-9, the weight of skeletal muscle protein was determined. G1 carcass protein was estimated using the Hankins and Howe equation since it was more accurate in predicting percentage carcass protein in this group. G2, G3 and G4 carcass protein was estimated by equation 3 (Table 5-8), 204 TABLE 5-7. GROUP MEANS AND STANDARD ERRORS FOR ACTUAL CARCASS BONE AND PREDICTED BONE FROM 9-10-11 RIBa Group Item 1 2 3 4 Carcass bone, % 17.1” 15.1” 13.4” 12.3” SE .47 .44 .18 .32 Hankins/Howe carcass bone, % 16.7” 15.6” 15.3” 14.5” SE .28 .26 .23 .23 Eqn #1 588255: 16.2” 14.5” 14.1” 12.8” SE .43 .40 .35 .35 a Calculated from Hankins and Howe (1946). Values within a column with different superscripts differ (P <.01). 205 .chHUMHSOHoU c“ poms can SHGO 60 I «0 Sony omumasoamo n .Aew I How MQDOHO Ham Scum omumHSOHmo m ov. mm. 66am. emom.m omHm mo cannons » m 66. 66. mmmmm. Hom.~ mmHm no seasons 6 m mm.H m6. mm6m. mmem.l mHm Ho mcon w a acmwOflmmmoo moanmehm> Hones: 0mm Na scammmummm ummououcH HCOUGTQUUGH coeumsom szeomm mmdomdo 024 mzom mmdom¢0 mw