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Boggs has been accepted towards fulfillment of the requirements for PhD degree in Animal Science December 11, 1981 Major professor RETURNING MATERIALS: MSU , Place in book drop to remove this checkout from w your record. FINES will be charged if book is returned after the date stamped below. TALLOW SUPPLEMENTATION AND SIMULTANEOUS PROTEIN WITHDRAWAL IN FINISHING RATIONS FOR LARGE FRAMED STEERS BY Donald L. Boggs A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Animal Science 1982 ABSTRACT TALLOW SUPPLEMENTATION AND SIMULTANEOUS PROTEIN WITHDRAWAL IN FINISHING RATIONS FOR LARGE FRAMED STEERS BY Donald L. Boggs Two feedlot trials and two rumen metabolism studies were conducted to evaluate the effects of tallow supplemen— tation and protein withdrawal. In feedlot Trial 1, steers fed low protein diets supplemented with 5% tallow (5%T) con- sumed less feed and had lower feed to gain (F/G) ratios than steers fed low protein diets without tallow (NC). In addi— tion the 5%T cattle had more external finish (BF), higher degrees of marbling and higher daily carcass fat deposition. Five percent tallow also increased the level of serum tri- glycerides and extractable lipid from the longissimus. In feedlot Trial 2, steers were fed NC, 5%T, low pro— tein, 7.5% tallow (7.5%T) or no tallow—high protein (PC) diets for 41, 82 or 123 days. Protein supplementation increased ADG, feed efficiency and quality grade. Cattle fed 7.5%T had lower ADC and lower intake. Maintenance of dietary energy intake was determined to be the key to suc— cessfully "force—finishing" large steers on a high tallow, low protein feeding regime. The effects of tallow supplementation (0 vs. 7.5%) and protein supplementation (8.5 vs. 12.0% CP) on rumen fermen— tation and digesta passage to the duodenum were estimated using 4 rumen fistulated steers, each fitted with a duodenal cannula. Tallow supplementation (T) increased lipid diges— tibility but did not effect ADF or cellulose digestibility. Dry matter (DM) and organic matter (OM) digestibilities were depressed by T only on the high protein (HP) diets. HP diets had higher DM, OM, ADF and cellulose digestibilities as compared to low protein (LP) diets. HP diets had higher levels of rumen ammonia. Tallow decreased total VFA cncen— tration. Tallow diets also increased the solid dilution rate. LP diets had a higher level of the N intake passing to the duodenum as NAN and on the no—tallow (NT) diets LP resulted in more undegraded, bypass protein. Tallow decreased synthesis of microbial CP and HP increased syn— thesis of MCP. In an in situ study of DM disappearance from nylon bags, neither tallow coating of feed nor dietary tallow affected the rate of DM digestion. ACKNOWLEDGEMENTS I would like to express my sincere appreciation to Dr. David R. Hawkins for his supervision, guidance and assis- tance throughout the graduate program. Gratitude is also expressed to Dr. Werner G. Bergen, Dr. Harlan Ritchie, Dr. J.T. Huber and Dr. Ronald Allen for their advice and assis- tance while serving as members of the guidance committee. Appreciation is expressed to Dr. W.T. Magee and Dr. Clyde Anderson for their assistance in the statistical analysis of the data presented. I have sincerely enjoyed the atmosphere of learning which prevails in the department due to the leadership of Dr. Ronald Nelson. His thorough knowledge and understanding of the livestock industry has been inspirational in my quest for such knowledge. A very special thanks is extended to Liz Rimpau and Elaine Fink for their help and expertise in laboratory pro— cedures. Special appreciation is also extended to Mrs. Pat Cramer for her friendship and ready assistance. The friend— ship and support of the faculty, staff and fellow students have certainly been enjoyed. My deepest love and gratitude are expressed to my wife, Rosemary. Her ability, talent and untiring effort were essential for the completion of this dissertation. However, the importance of these efforts are minute when compared to the importance of her love, patience and understanding. The completion of this dissertation culminates a long educational process. To reflect upon the many people who have contributed to my progess throughout the various stages of my educational career is very heart—warming. I feel for— tunate to have become friends with so many students, faculty, staff and fellow graduate students at schools across the country. ii TABLE OF CONTENTS LIST OF TABLES . . . . . . . . . . . . . . LIST OF PROCEDURES . . . . . . . . . . . . . . . . . . Vii INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 1 REVIEW OF LITERATURE . . . . . . . . . . . . . . . . . . 2 SUPPLEMENTAL FAT IN RUMINANT RATIONS . . . . . . . . . 2 A. Energy Considerations and Digestibilities of Fat Sources . . . . . . . . . . . . . . . . . B. Rumen Metabolism of Lipids . . . . . . . . . . . C. Blood Lipids and Adipose Tissue Metabolism . . . D. Effect of Fat on Voluntary Intake and Energy Intake . . . . . . . . . . . . . . . . . 9 E. Effect of Fat on the Digestibility of Ration Components . . . . . . . . . . . . . . . . . . .12 F. Effect of Fat on Rumen Fermentation and Passage Rate . . . . . . . . . . . . . . . . . .17 G. Effect of Fat on Feedlot Performance . . . . . .21 H. Effects of Supplemental Fat on Carcass Composition . . . . . . . . . . . . . . . . . .23 UTUJN WITHDRAWAL OF SUPPLEMENTAL PROTEIN FROM FINISHING RATIONS . . . . . . . . . . . . . . . . . .26 A. Effects of Level and Source of Protein on Feedlot Performance and Carcass Characteristics 26 B. Level of Nitrogen Intake Effects on Rumen Metabolism and Microbial Protein Synthesis . . .28 C. Effect of Level of Nitrogen on Digestibility of Ration Components . . . . . . . . . . . . . .31 USE OF MARKERS IN RUMEN PASSAGE AND DIGESTIBILITY STUDIES . . . . . . . . . . . . . . . .33 LITERATURE SUMMARY . . . . . . . . . . . . . . . . . .38 TALLOW SUPPLEMENTATION AND SIMULTANEOUS PROTEIN WITHDRAWAL IN FINISHING RATIONS FOR LARGE FRAMED STEERS SECTION I. EFFECTS ON FEEDLOT PERFORMANCE AND CARCASS CHARACTERISTICS . . . . . . . . .40 Introduction . . . . . . . . . . . . . . . . . . . .40 Materials and Method . . . . . . . . . . . . . . .42 Results and Discussion . . . . . . . . . . . . . . .46 iii —W~_——s—--—m m—r’s:r~ w, ,, ::< * * SECTION II. EFFECTS ON RUMEN FERMENTATION, MICROBIAL PROTEIN SYNTHESIS AND IN SITU NUTRIENT DISAPPEARANCE . . . . . . . . .60 Introduction . . . . . . . . . . . . . . . . . . . .60 Materials and Methods . . . . . . . . . . . . . . .61 Results and Discussion . . . . . . . . . . . . . . .67 Summary . . . . . . . . . . . . . . . . . . . . . .83 APPENDIX . . . . . . . . . . . o o o n o o o a o o o o 086 LITERATURE CITED . . . . . . . . . . . . . . . . . . . .99 iv —~4—MI ' ' ' 3r -fi'v’. ‘34; T 1‘ 1 1-3. l—4. 1-5. 1—6. 1—8. 1—9. LIST OF TABLES Composition of experimental diets (Trials 1 and 2) . . . . . . . . . . . . . . Diet effects on feedlot performance (Trial 1) Diet effects on feedlot performance (Trial 2) Diet effects on carcass composition (Trial 1) Treatment means of carcass measurements as affected by diet and time on feed (Trial 2) . Treatment means for carcass composition and daily carcass protein, fat and energy gains (Trial 1) . . . . . . . . . . . . . . . . . . Diet effects on percent carcass fat, daily fat and estimated protein deposition and estimated daily carcass energy gain (Trial 2) Diet effects on intramuscular fat and serum triglceride (Trial 1) . . . . . . . . . . . . Comparison of predicted versus actual live weight gains . . . . . . . . . . . . . . . . Composition of experimental diets (digestibility—passage study) . . . . . . . . Effects of tallow supplementation and protein withdrawal on apparent rumen digestion of dry matter, lipid, acid detergent fiber and cellulose . . . . . . . . . . . . . . . . . . Effects of tallow supplementation and protein withdrawal on rumen ammonia concentration . . Effects of tallow supplementation and protein withdrawal on rumen volatile fatty acids .. . Effects of tallow supplementation and protein withdrawal on rumen volume and rumen dilution rates . . . . . . . . . . . . . . . . . . . . Effects of tallow supplementation and protein withdrawal on nitrogen flow to the duodenum . Page .43 .47 .48 I50 .51 .54 .55 .57 .58 .62 .68 .70 .73 .75 .76 2—7. Effects of tallow supplementation and protein withdrawal on efficiency of microbial protein synthesis . . . . . . . . . . . . . . . . . . . . .79 2—8. The effect of dietary tallow and tallow coating of feed on the disappearance of dry matter, extractable lipid and crude protein from samples incubated in the rumen of steers . . . . .82 A-l. Individual steer data - steer 112 . . . . . . . . .86 A—2. Individual steer data — steer 158 . . . . . . . . .87 A-3. Individual steer data — steer 325 . . . . . . . . .88 A—4. Individual steer data — steer 388 . . . . . . . . .89 vi Procedure lA. Preparation of Chromium—EDTA solution 2A. Preparation of Ytterbium marked feed 3A. Feeding and sampling scheme for rumen digestibility study . . . . . . . . . 4A. Isolation of rumen bacteria . . . . . 5A. Procedure for determining D-alanine . 6A. Rumen ammonia analysis . . . . . . . 7A. Procedure for nylon bag experiments . 8A. Sample calculations for passage experiment LIST OF PROCEDURES vii passage— 9 o Page 090 .91 .92 .93 .94 .96 .97 .98 INTRODUCTION The incorporation of the larger framed European breeds of cattle into United States beef herds has forced changes in both feeding and marketing strategies of feedlot opera— tors. These later maturing cattle are typically leaner at given weights than their British breed counterparts. There— fore these larger framed cattle require more days on feed and must be taken to heavier weights to attain a desirable degree of finish and to reach the choice grade. With the recent spiraling of non—feed costs creating a need for a more rapid feedlot turnover, the extra time on feed required by these cattle has become a more dramatic disadvantage. The development of a feeding regime to reduce the time on feed and perhaps change the pattern of fattening to a more rapid deposition of intramuscular fat could therefore be very profitable. Such a system would allow the beef industry to take advantage of the ability of larger—framed cattle to grow rapidly and efficiently at lighter weights, yet still market a consumer acceptable product at a young age and a moderate carcass weight. This project was designed to study the effects of withdrawing supplemental protein and increasing dietary energy, via supplemental tal- low, on large—framed feedlot steers during the terminal fin— ishing period and to determine the feasibility of this feed— ing system in accomplishing the aforementioned goal. PM. 4.? - ;.1,_ -— REVIEW OF LITERATURE SUPPLEMENTAL FAT IN RUMINANT RATIONS A. Energy Considerations and Digestibilities of Fat Sources The addition of supplemental fats is an easy method to increase the caloric density of animal diets. On a caloric basis, fat will provide 2.25 times the energy of carbohy- drates and proteins. Lofgreen (1965) found the NEp for tal— low to be 2.59 Mcal/Kg when added at levels of 2.5, 5.0, 7.5 and 10 percent of the diet as compared to a barley diet reference standard with an NEp of 1.06 Mcal/Kg. Swift and Forbes (1944) showed that a further benefit of adding fat to carbohydrate—protein diets was a decrease in the specific dynamic effect or heat increment. Addition of 10 percent fat to a high carbohydrate diet for lambs fed at 1780 Kcal of energy intake per day resulted in a 45 Kcal increase in metabolizable energy (ME) and a 68 Kcal increase in net energy (NE) (Black, 1971). He concluded these increases were due to a reduction in the energy lost as methane and a decrease in the heat of fermentation. Czerkawski gt 31. (1966b) reported decreases in both methane production and urinary energy losses resulting in an increase in metaboliz- able energy of 9.5 Kcal/lOO g of diet when linseed oil was added to sheep diets. Continuous infusion of unsaturated fatty acids depressed methane production and resulted in ME values for the fatty acids of 104 percent of their heat of combustion (Czerkawski gt 31., 1966a). Most sources of fat are highly digestible. Andrews and Lewis (1970a) used sheep energy balance trials to determine digestibility coefficients for several lipid supplements. They compared coefficients of digestibility corrected for the lipid in the basal ration with uncorrected values for apparent digestibility determined by total lipid input and output. Following are the respective corrected and apparent digestibility coefficients for beef tallow (85.1%, 78.5%), hydrolyzed—esterified fat (74.2%, 70.8%), soybean oil (83.1%, 78.0%) and maize oil (78.3%, 70.3%). Corrected digestibility coefficients of partially purified samples of lauric, myristic, palmitic, stearic and oleic acids ranged from 81 to 93 percent (Andrews and Lewis, 1970b) with a slight decrease in digestibility occurring as the chain length of the fatty acid increased. Oltjen (1975) summar— ized that, after making corrections for fecal soaps, the true digestion coefficients for added fats is 95 percent. B. Rumen Metabolism of Lipids In the rumen, dietary lipids undergo three metabolic processes. These are: (l) hydrolysis of esterified fatty acids; (2) hydrogenation of the double bonds of unesteri— fied, unsaturated fatty acids; and (3) fermentation of the glycerol released during hydrolysis (Oltjen, 1975). Hydro- lysis of esterified lipids occurs rapidly via the action of lipolytic bacteria (Palmquist and Jenkins, 1980) and is a necessary step, and perhaps the rate limiting step, in the biohydrogenation of the unsaturated fatty acids. Hydrogena— tion results in an energy savings for ruminants since the double bonds of unsaturated fatty acids act as hydrogen acceptors, thus decreasing the production of methane (Black, 1971). Shorland _£ _1. (1957) incubated oleic, linoleic and linolenic acids with sheep rumen contents and found all three of these unsaturated acids resulted in the production of saturated stearic acid. They concluded the reason that ruminant depot fat does not resemble dietary fat is the ruminal hydrogenation of dietary unsaturated fatty acids, particularly linolenic acid. However, the degree of hydrogenation may be incomplete. Clarke and Roberts (1967) found that feeding different mixtures of fatty acids to give varying degrees of unsaturation, all resulted in increases in fecal stearic acid. However, the proportion of stearic acid in the feces decreased as the degree of unsaturation increased. Palmquist and Jenkins (1980) found reports of the degree of biohydrogenation of the C:18 unsaturated fatty acids ranging from 68 to 90 percent. The glycerol end—product of lipolysis is fermented in the rumen to propionic acid. Black (1971) found this conversion to be the most significant loss of energy in the digestion of fat in the rumen, although it still represented only 0.4 percent of the energy of fat. Lipids are also synthesized by rumen microbes. Rumen bacterial lipids are characterized by a high content of branched—chain and odd-carbon fatty acids (Oltjen, 1975) and are considered an important source of lipids to the host animal (Palmquist and Jenkins, 1980). C. Blood Lipids and Adipose Tissue Metabolism The long—chain fatty acids are not soluble in the rumen digesta but do attach to food particles in the rumen and are thus passed into the small intestine (Harrison and Leat, 1975). In the small intestine the fatty acids are emulsi- fied with bile, formed into micelles, and absorbed into the blood stream. In the blood, the fatty acids bind to blood proteins, primarily albumen, and equilibrate rapidly with the fatty acids of tissue (Emery, 1979). The uptake of lipids from the blood is mediated by the triacylglycerol acyl hydrolase, lipoprotein lipase. The fats which are incorporated into body fat depots come from either the diet or tissue synthesis. When dietary fat is high, preformed fats absorbed from the digestive tract are the major sources. However, when dietary fat is low, the ruminant relies upon d3 3222 synthesis of fatty acids as the major source of tissue fat (Bauman, 1974). Whereas non—ruminant species utilize glucose as the primary substrate for fatty acid synthesis, the ruminant relies upon acetate from rumen fermentation as the primary precursor for m:;. , fatty acid synthesis in both adipose and mammary tissue (Emery, 1979). This dependence on acetate is most evident, at the production level, in the “low fat—milk syndrome" in dairy cows which occurs with high grain-low fiber diets that result in a decreased acetate/propionate ratio (Bauman, 1974). To be utilized, the acetate must be converted to acetyl CoA via the mediation of acetyl CoA synthetase. This enzyme is not present in ruminant liver cells, hence conver- sion of acetate to fatty acids in ruminants occurs primarily in the adipose tissue (Ricks, 1979). Acetyl CoA carboxylase mediates the conversion of acetyl CoA to malonyl CoA and is considered to be the rate limiting enzyme for fatty acid synthesis within the adipose cell (Bauman, 1974). Large quantities of NADPH reducing equivalents are also necessary for fatty acid synthesis. The pentose—phosphate cycle and the isocitrate cycle are the primary producers of these reducing equivalents. Glucose—6-phosphate dehydrogenase and isocitrate dehydrogenase are the respective regulatory enzymes of these two pathways (Bauman and Davis, 1975). Feeding high levels of dietary fat generally reduces the activity of the enzymes associated with fatty acid syn— thesis (Yang st 31., 1978). These workers found high levels of dietary fat reduced in vitro rates of lipogenesis from acetate and glucose and increased in vitro rates of fatty acid release from adipose tissue. They also found an increase in lipoprotein lipase activity in adipose tissue, indicating an increase in the uptake of preformed fatty acids from the blood. A similar result was reported by Ben— son gt gt. (1972) when lactating cows were switched to restricted roughage rations. These activities resulted in a depression of milk fat percentage. Adding fat to ruminant rations commonly results in increases in the blood lipids (Stull gt gt., 1957; Mata- Hernandez gt _t., 1978). Bohman gt gt. (1962) found increases in plasma fat, cholesterol and plasma lipid phos- phorous when one half pound of fat was fed to wintering steers. The highest increases were reported when fat was added to low protein wintering rations. Wrenn gt _t. (1978) fed protected and unprotected fat as ten percent of the con— centrate for dairy cows and reported increases in plasma cholesterol and lipids of 1.7 times control for the pro— tected fat and 1.5 times control for the unprotected fat. This apparently is not an energy effect as Qureshi gt gt. (1972) fed all hay, hay—grain and high grain diets, and found no significant differences in proportions of blood lipids (triglyceride, free cholesterol, free fatty acids, cholesterol esters and phospholipids) between the diets. Macleod gt gt. (1972) added three percent tallow or three percent soybean oil to a low fat basal ration and found both types of fats would increase the plasma lipid fractions. They also reported the soybean oil increased stearic and oleic acids and decreased the shorter chain acids, whereas the tallow had no effect on the proportions or yields of fatty acids in milk. Marchello gt gt. (1972) found 6% safflower oil increased the unsaturated fatty acids in serum although neither the safflower oil nor 6% tallow had significant effects on the serum lipid levels. Marchello _t _t. (1971) added 0, 5, 10 and 15% animal fat to rations containing 60, 75 and 90% concentrate. Across all concentrate levels, the 5 and 15% fat levels increased serum lipids 36% while the 10% fat level resulted in 73% higher lipid levels. However, the 90% rate level resulted in lower serum lipids due possibly to a decrease in lipid absorption. Using similar diets, Dryden gt gt. (1971) reported high density lipoproteins (HDL) made up 76% of the total lipoproteins and contributed 41% of the lipid. The control steers had the lowest lipoprotein levels and the 10% fat supplemented steers had higher levels than the 5 and 15% supplemented steers. Similar results were reported for the quantity of lipids in the HDL and LDL (low density lipopro— teins). Protected fats which escape rumen fermentation also increase the blood lipid levels. Dryden gt gt. (1975) com— pared rations containing 6% unprotected safflower oil or 6% safflower oil complexed with 6% casein to control diets. The protected lipid resulted in increases in serum lipids of 2.1 times the control and 1.7 times the unprotected lipid. Serum LDL levels after 168 days on feed were four times higher for the protected lipid and the same diet resulted in increased linoleic acid in the serum. Palmquist and Mattos (1973) reported increases in total lipids and triglycerides in both serum and the LDL fraction when full—fat soy flour was fed both in protected and unprotected form. However, free cholesterol was higher only in the serum and not the LDL fraction. Kronfeld gt gt. (1980) fed protected tallow to provide 25% of the ME as fat for lactating cows and reported increases in plasma glucose and serum cholesterol and decreases in the concentrations of acetoacetate and B— hydroxybutyrate in plasma. D. Effect of Fat on Voluntary Intake and Energy Intake As previously discussed, additions of fat to ruminant rations increase the caloric density of these diets. In most cases, the feeding of these fat supplemented diets results in an increase in dietary energy intake (Bull, 1971). This appears to be most likely when fats, both saturated and unsaturated, are added at levels less than 5% of the total diet (Palmquist and Conrad, 1978; Macleod and Wood, 1972). Inclusion of supplemental fat above 5% of the total diet tends to decrease voluntary feed intake (Wray gt gt., 1980; Dyer gt gt., 1957). Figroid gt gt. (1971) reported an 11% decrease in feed intake with 10% tallow and a marked intake reduction with 15% tallow added to high con— centrate diets, although additions of 5% and 10% fat to 90% concentrate diets resulted in increased digestible energy intake per 100 pounds of body weight. Marchello gt gt. 10 (1971) reported feed intakes of 2.2 and 1.9% of the body weight when 10 and 15% levels of animal fat were added as compared to intakes of 2.5% of the body weight when 0 or 5% animal fat was added to the diet. Bull (1971) suggested the need for research concerning energy intake as a control of voluntary feed intake when fats are added to the diet. Dinius gt gt. (1975) reported data which would support this theory as a possible explana- tion for depressed intake when feeding high levels of fat. They fed a protected oil—casein complex (350% oil) at 0, 10, 20 and 30% of the diet of steers and found feed intake decreased linearly as the percent complex in the diet increased to facilitate equal intakes of the fat supplement complex among the treatments. Macleod gt _t. (1977) reported no differences in energy intakes when dairy cows were fed protected tallow at 5.0, 13.3 and 18.6% lipid in the diet dry matter, supporting the theory that cattle eat to a constant level of fat, regardless of ration concentra— tion. Other data support more than simple quantitative energy control as the reason for the depression in intake. Haaland _t _t. (1981) fed 5 or 10% protected tallow in high energy diets formulated to contain equal amounts of metabolizable energy and realized a depression in intake by the cattle receiving 10% fat. Both Faichney gt gt. (1972) and Cuitun t l. (1975) reported decreases in digestible energy intake 11 when feeding protected lipids to supply 8.8% and 6% lipid to the diet. Roberts and McKirdy (1964) suggested a decrease in microbial activity as an explanation for a reduction in feed intake by cattle fed 10% tallow. Kowalczyk gt gt. (1977) reported a decrease in the voluntary intake of dried grass by lambs when a high fat supplement (=66% tallow) was added at 7 and 14% of the estimated intake. However, when this supplement was suspended in a liquid to bypass rumen fermentation, the voluntary intake was not significantly altered. Johnson and McClure (1973) added graded levels of hydrolyzed, esterified fat (HEF) or corn oil to corn plant material prior to ensiling. Voluntary intake of the silages with added fat was lower than the control with the lowest intake occurring on the 12% HEF silage. They recorded intakes of digestible fat of 4.9 and 4.8 grams per unit of metabolic weight for sheep and cattle respectively, versus 1.4 grams of digestible fat intake per unit of metabolic weight for the control silages. Addition of 1% limestone to the silages with added fat resulted in higher intakes. Buchanan—Smith, gt gt. (1974) reported an animal fat x nitrogen source interaction on voluntary intake of low roughage rations. Addition of 5% fat to soybean meal sup— plemented diets increased intake 10% whereas fat added to urea supplemented diets decreased intake 5%. 12 E. Effect of Fat on the Digestibility of Ration Components Literature reports on the effect of supplemental fat on the digestibilities of the various ration components are highly variable. A decrease in the digestibilities of dry matter and organic matter are generally reported ¢rskov gt gt., 1978; Davison and Woods, 1960; Dyer gt gt., 1957). Czerkawski (1966) reported increases in the excretion of total fecal dry matter but decreases in the amount of lipid-free, cellulose-free dry matter in the feces when fat was added to the diet. Bradley gt gt. (1966) reported decreases in the digestibilities of dry matter and energy when 5% fat was added alone and with urea to steer finishing rations. Steele and Moore (1968) reported a decrease in dry matter digestibility when palmitic and stearic acids were given to sheep but no change when myristic acid was given. They noted an inverse relationship between the melting points and digestibilities of the fatty acids. In contrast Hatch t l. (1972) reported no change in dry matter diges— tibility when either 3 or 6% animal fat was added to beef cattle rations and Kronfeld and Donoghue (1980) reported an improvement in the digestibility of dry matter when feeding protected tallow. Addition of fat at low levels has been shown to increase the total digestible nutrients (TDN) of ruminant diets (Bohman and Lesperance, 1962) and increase the diges— tibility of the ration energy (Esplin t al., 1963). How- 13 ever, Figroid gt _t. (1971) reported decreases in the diges— tibility of gross energy when 10% or 15% tallow was added to 60% and 90% concentrate diets. Phillips and Roberts (1966) administered sunflower seed oil both orally and duodenally and found no difference in the digestibility of dietary energy due to site of administration. However with the oral administration of oil, the digestible energy occurring from the oil was higher and the digestible energy arising from fiber was lower. Little and Mitchell (1965) found 4—5% decreases in the digestibility of energy when either lard or corn oil was administered abomasally rather than orally. Consistent increases in the digestibility of ether extract have been observed when fats are added to ruminant rations (Palmquist and Conrad, 1978; Bradley gt gt., 1966; Esplin gt gt., 1963; Bohman and Lesperance, 1962; Davison and Woods, 1960). However, Figroid gt gt. (1971) recorded significant increases in fecal soaps of 7, 21 and 19% on diets containing 5, 10 and 15% tallow. They concluded, at high levels of fat feeding, estimations of fat digestibili— ties determined by ether extract were high. Phillips and Roberts (1966) found total fat digestibility to be 16-27 units lower than ether extract digestibility and suggested using total fat digestibility when assessing the value of supplemental fat and oil. Esplin gt gt. (1963) also noted increases in fecal soaps but they felt the absolute increases were relatively small and thus fecal soaps did not represent a major loss of energy from added fats. l4 Czerkawski (1966) also reported an increased fecal excretion of bacterial fatty acids when the level of dietary fat increases. Czerkawski gt gt. (1966b) found the proportion of bacterial fatty acids decreased and the proportions of C:18 fatty acids increased in the feces, but the total quan- tity of bacterial fatty acids excreted in the feces remained constant since the total output of fecal fatty acids increased. Depressions in the digestibilities of crude fiber and cellulose have also been consistently reported when fats and oils are fed to ruminants (Phillips and Roberts, 1966; Gra— inger gt gt., 1961; Dyer gt gt., 1957; Devendra and Lewis, 1974; Bohman and Lesperance, 1962; Davison and Woods, 1960; Kronfeld and Donoghue, 1980). Brooks gt gt. (1954) incu- bated 10 to 170 mg of corn oil with 1 gram of 50% cellulose dry matter and found reductions in tg vitro cellulose diges— tibility of 40 to 94%. In another experiment these workers found additions of 32 and 64 grams of corn oil to lamb rations reduced cellulose digestibility 52 and 70% respec- tively and equivalent levels of lard reduced cellulose digestibility 33 and 53%. Little and Mitchell (1965) recorded decreased cellulose digestibilities of 4.8 and 11.5% respectively when 10% lard or 10% corn oil was given orally as compared to administering the same quantities of these fats abomasally. Czerkawski (1966) observed approxi— mately a 1% depression in cellulose digestibility for each 1% increase in the level of dietary fat. 15 Devendra and Lewis (1974) offered the four following theories to explain the depressed fiber digestibility which accompanies fat supplementation: l. A physical coating of the fiber with fat prevents attack by the rumen microbes. 2. A modification of the rumen microbial population con- cerned with cellulose digestion. Fat possibly is toxic to some microorganisms. 3. Inhibition of microbial activity brought about by absorption of fatty acids on the cell walls changing cell permeabilities. 4. Reduced cation (Ca+, Mg+) availability as a result of formation of insoluble complexes with long chain fatty acids. Orskov _t gt. (1978) sprayed tallow on dried grass at rates of 0, 50, 100 or 150 g/Kg and incubated these samples in the rumens of lambs fed either fat-treated or untreated grass. They found no difference in the rate of disappear- ance for any of the levels of tallow. They concluded that tt the depression of fiber digestibility is due to physical coating of the fiber, then the coating is from non- esterified fatty acids in the rumen and not from dietary triglycerides. The effects of supplemental fats on nitrogen and crude 16 protein digestibilities have been highly variable. Little and Mitchell (1965) and Czerkawski (1966) each reported no change in the digestibility of crude protein when fat was added to the diet. Kronfeld and Donoghue (1980) reported an increase in protein digestibility when feeding protected tallow and Palmquist and Conrad (1978) suggested a benefi— cial fat x protein interaction on nitrogen digestibility when 3% fat was added to high protein diets. In contrast, Bradley, gt gt. (1966) reported significant decreases in crude protein digestibility when fat and urea were added simultaneously. Decreases in protein digestibility of 17 and 36% were recorded when 32 and 64 grams of corn oil were added to lamb diets (Brooks gt gt., 1954). Phillips and Roberts (1966) reported an increase in nitrogen retention when oil was given orally as compared to duodenal adminis- tration. Robinson gt _t. (1956) observed a decrease in uri- nary nitrogen and an increase in total nitrogen retention when 200 grams of corn oil were added to wintering rations of steers. Thompson gt gt. (1967) found the inclusion of fat in the diet significantly reduced the utilization of nonprotein nitrogen in the rumen. Dietary fats have been found to decrease the digesti- bility of the ash content of feeds (Davison and Woods, 1960), especially calcium (Grainger gt gt., 1961; Kronfeld and Donoghue, 1980). Grainger gt gt. (1961) found the addition of 4.4 grams of calcium or 6.2 grams of iron per day to the ration partially alleviated the negative effects 17 of corn oil on cellulose digestibility. Brooks gt gt. (1954) noted similar results when alfalfa ash was added to rations supplemented with lard and corn oil. Davison and Woods (1961) reported the addition of CaCO3 to corn cob diets supplemented with corn oil resulted in increased digestibility coefficients for organic matter, energy, pro- tein and cellulose. F. Effects of Fat on Rumen Fermentation and Passage Rate The literature reports several rumen parameters are affected by supplemental fat feeding; however, these effects have been quite variable. Czerkawski gt gt. (1975) found the number of protozoa decreased and the number of bacteria increased when 90 grams of linseed oil was added to 900 grams of a basal diet, but Brooks gt gt. (1954) reported similar numbers of bacteria between basal diets and those supplemented with lard. These workers also reported that addition of high levels of corn oil resulted in white, tur— bid rumen contents with a putrid odor. Kowalczyk _t _t. (1977) observed increases in pH and linear decreases in rumen ammonia when graded levels of tal- low emulsions were infused into the rumen of sheep. This increase in pH would follow with the Devendra and Lewis theory on reduced cation availability when fat levels are high.' Macleod and Wood (1972), on the other hand, found no effect on pH or rumen ammonia concentration when adding 3% 18 tallow or 3% soybean oil to basal rations. Rumen ammonia was not affected when tallow and blended vegetable fat were added as 10% of the concentrate which was fed as 50% of the diet dry matter for lactating dairy cows (Palmquist and Con- rad, 1980). Rumsey _t _t. (1971) reported a decrease in ruminal ammonia concentration when orchard grass pasture was supplemented with ground corn and fat as compared to molasses and urea. Phillips and Church (1975) reported a decrease in the tg vitro disappearance of ammonia from 4.71 to 3.30 mg/100 ml when 3% tallow was added to varying levels of carbohydrate. They also found a tallow x urea interac- tion for decreased ammonia disappearance. Shaw and Ensor (1959) observed an increase in the con- centration of total volatile fatty acids (VFA) in the rumen fluid when feeding unsaturated fats and fatty acids. How— ever, lard decreased the level of VFA in the rumen contents of lambs from 4.1 to 2.4 mg/100 ml (Brooks gt gt., 1954). Czerkawski _t gt. (1975) observed a similar decrease in the rumen VFA concentration when feeding linseed oil, however, the capacity of the rumen contents to produce VFA tg vitro increased with the high fat diet. Kowalczyk gt gt. (1977) observed a linear increase in the concentration of free fatty acids with increasing levels of tallow. Increases in dietary fat consistently resulted in a decrease in the proportion of acetic acid and an increase in the proportion of propionic acid in the rumen fluid (Thomp— l9 son gt _t., 1967; Shaw and Ensor, 1959; Palmquist and Con- rad, 1980; Palmquist and Conrad, 1978). Atypically, Johnson and McClure (1972) reported no effect of supplemental fat on molar proportions of VFA. Clarke and Roberts (1967) found the acetic to propionic acid ratio decreased as the level of unsaturation increased when fatty acids were mixed to give varying degrees of unsaturation. Phillips and Church (1975) found in vitro acetic acid production decreased and in vitro propionic acid production increased when 3% tallow was added to varying levels of carbohydrate. They also reported a tallow x urea interaction which resulted in decreased pro- duction of acetic and butyric acids. Czerkawski gt gt. (1975) reported increases in the dilution rate and the volume of the rumen contents when adding linseed oil to diets for sheep. High levels of tal— low injected into the rumen resulted in a decrease in the rate of digestion of grass and cotton thread (98% cellulose) (Kowalczyk gt _t., 1977). They suggested this decrease in the rate of fermentation could effect both retention time and voluntary intake. These workers also noted rapid decreases in the rate of digestion when the concentration of free fatty acids in the rumen liquor exceeded 5 mM. Phil— lips and Roberts (1966) compared the effects of oral versus duodenal administration of sunflower seed oil and soybean protein on the rate of rumen fermentation (RFR). They con— cluded that RFR was not closely related to fiber digestion and found no significant effects of oil on RFR. However, 20 since the highest RFR occurred with oral oil-oral protein and the lowest RFR occurred with oral oil—duodenal protein, they suggested the 7.4% crude protein level of the basal ration was too low to support maximal fermentation rates in the presence of supplementary oil. As was previously discussed, the feeding of supplemen— tary fats to ruminants generally results in a decrease in methane production. Czerkawski gt gt. (1966a) reported a reduction of 0.24 moles of methane per mole of double bonds and estimated the reduction in methane production on an energy basis for the addition of the three primary 18 carbon unsaturated fatty acids to be 13.8 Kcal CH4/100 Kcal of oleic aCidr 14-2 Kcal CH4/100 Kcal of linoleic acid, and 16.4 Kcal CH4/100 Kcal of linolenic acid. Czerkawski (1966) observed a 30% reduction in methane production (17 Kcal CH4/100 Kcal of additional fatty acids) when sheep were slowly adapted to high levels of fat over a period of weeks. A reduction of 28.9 Kcal CH4/100 Kcal of fatty acid occurred when sheep were not adapted to the high levels of fatty acids (Czerkawski gt gt., 1966b). These workers further compared a slow, continuous infusion of fatty acids versus a rapid administration of an equal quantity of fatty acids into the rumen. The continuous infusion decreased methane production 16.3 Kcal/lOO Kcal of fatty acid, whereas the rapid administration of the fatty acids decreased methane production 28.0 Kcal/lOO Kcal of fatty acid. Czerkawski gt al. (1978) observed a 23% depression in methane production 21 and a 17% decrease in VFA production when tallow was added to hay and barley using the Rusitec Rumen Simulation Tech- nique. Addition of whey to the tallow compensated for the detrimental effects of the tallow by increasing the rate of fermentation. G. Effect of Fat on Feedlot Performance Addition of low levels of fat to beef finishing rations has been a routine practice in many feedlots to control dust in the feed and facilitate the mixing of ingredients. Addi— tions of fat up to 5% of the diet dry matter have been shown to have a positive effect on feedlot performance (Bull, 1971). Many of the reported trials have recorded a decrease in feed intake with no effect on rate of gain to indicate an increase in the efficiency of feed conversion (Hubbert gt gt., 1961; Devier and Pfander, 1974; Willey gt gt., 1952). Hentges gt gt. (1954) reported an increase in the rate of gain of steers receiving 5% raw ground waste beef fat and a decrease in the feed required for gain when both 5 and 10% of the fat were added. A 28% increase in gain and a 23% decrease in the feed to gain ratio was observed by Bohman gt a1. (1957) when 5% fat was added to fattening rations for steers and a 16% decrease in the feed to gain ratio was observed when 10% fat was added. They attributed this increase in performance and efficiency to an improved calorie to protein ratio. Bohman gt gt. (1959) reported no effect on gain when 0.5 pound animal fat per day was given 22 to steers wintered on grass hay, however, the fat supple— mented steers did record higher gains during the following summer. Erwin _t _t. (1956) found the addition of tallow increased the rate of gain of steers on alfalfa, but decreased the rate of gain of steers receiving wheat straw. Effects of fat on performance at levels greater than 5% of the diet have been more variable. Lofgreen (1965) reported no difference in performance except for decreases in the feed to gain ratio as the fat level increased when 0, 2.5, 5, 7.5 and 10% tallow was added to barley rations. Marchello gt gt. (1971) showed decreases in average daily gains for steers fed 10 or 15% animal fat when compared to those fed 0 or 5%. Feed efficiency was improved with all three levels of fat although the highest feed efficiency occurred with the 5% tallow diets. Feeding a protected tal- low supplement to supply approximately 8% tallow in the diet resulted in an increase in gain and feed efficiency (McCar- tor and Smith, 1979). However, Faichney gt gt. (1972) noted slower gains when steers were fed similar levels of a pro— tected lipid supplement and Dinius gt gt. (1975) reported a linear decrease in gains as the quantity of a protected casein—oil complex increased from O to 10 to 20 to 30% of the diet. Haaland gt gt. (1981) observed decreases in live weight gains and feed efficiency when the protected tallow intake of steers increased from 5% to 10% of the ration. Bradley gt gt. (1966) found simultaneous additions of 23 fat and urea consistently depressed the rate of gain of fin— ishing steers. Hatch _t _t. (1972) reported similar results when 3 or 6% animal fat was added to urea supplemented rations. Addition of calcium did not improve the feedlot performance in either experiment. In contrast, Buchanan— Smith gt gt. (1974) reported no significant effects on aver- age daily gain or feed to gain ratio when 5% animal fat was added to either soybean meal or urea supplemented finishing rations. H. Effects of Supplemental Fat on Carcass Characteristics Reports of effects of feeding supplemental fat on the body composition of finishing steers has been highly vari— able. Lofgreen (1965) and Wray gt gt. (1979) observed no effects of dietary tallow on carcass characteristics. Hentges gt gt. (1954) found no differences in carcass qual— ity grade or organoleptic tests when either 5 or 10% raw ground waste beef fat was added to fattening rations for steers. Buchanan—Smith gt gt. (1974) found the addition of 5% fat in the diet resulted in an increase in backfat and liver fat, while Edwards gt a1. (1961) reported increases in separable rib fat when 5% animal fat was added to the diets of steers which had previously received low energy rations but not when steers had previously received high energy diets. Bohman gt gt. (1957) recorded a non—significant increase in quality grade from High Good to Low Choice when fat was added to the diet. Significant increases in 24 marbling score and quality grade were noted by McCartor and Smith (1978) when a protected tallow supplement was fed to provide 8% tallow in the diet. Dinius gt gt. (1975) found greater increases in intramuscular fat than in the other fat depots when protected tallow was fed to finishing cattle. In contrast to the other reports, Willey gt gt. (1952) observed a decrease in the percent fat and an increase in the percent protein in the 9—10—11 rib cut of steers fed high and low energy basal diets containing 5% cottonseed oil. They also reported decreases in the ether extract of the longissimus dorsi of the fat supplemented steers. Steers receiving tallow had a lower percent retail yield than control steers with the percent kidney and pelvic fat estimate being the most highly influenced parameter (Haaland _t gt., 1981). These workers also noted that, on a constant carcass weight basis, tallow fed steers were fatter as determined by carcass specific gravity than the control steers, but there was no difference between diets in the percentage of the steers grading Choice. Considerable attention has been given to the effect of supplemental dietary fats on the fatty acid composition of the body depot fats. In general, the addition of highly saturated animal fat has had very little effect on the fatty acid composition of the body fat stores (Dryden gt gt., 1973; Dryden and Marchello, 1973; Johnson and McClure, 1972). However, the addition of unsaturated dietary fats results in an increase in the degree of unsaturation of 25 fatty acids in the depot fat (Dryden and Marchello, 1973; Dryden gt gt., 1973). When unsaturated fats are protected from ruminal digestion these increases are more pronounced. Marchello gt gt. (1973) reported the linoleic acid content of subcutaneous fat obtained by biopsy was tripled after 56 days on a protected safflower oil supplement. Dinius gt gt. (1975) reported similar results, although they noted the changes in tissue fatty acid composition of finishing cattle were not as pronounced as the changes in lighter weight cat- tle. WITHDRAWAL OF SUPPLEMENTAL PROTEIN FROM FINISHING RATIONS A. Effects of Level and Source of Protein on Feedlot Performance and Carcass Characteristics Supplementary protein is generally the most expensive ingredient in beef feedlot rations. Therefore, a consider- able savings in the cost of feed would be realized if sup— plementary protein could be withdrawn from the ration. There is strong evidence indicating decreases in gain and feed efficiency when the level of protein is decreased in diets for steers in the growing or early finishing phase of the feeding period (Hanson and Klopfenstein, 1979; Raleigh and Wallace, 1963; Bohman gt gt., 1959; Winchester gt gt., 1957). Peterson gt gt. (1973) reported positive linear increases in weight gains and feed efficiency of growing— finishing cattle when high energy diets were supplemented to 9, ll, 13 and 15% crude protein. High silage diets, how— ever, did not respond to the increases in crude protein. Hubbert gt gt. (1961) found decreases in average daily gain and feed efficiency when steers were fed 10% crude protein diets throughout the feeding period as compared to 13% crude protein diets. However, long—fed steers did not respond to increasing crude protein from 10 to 14%. During the terminal phases of the finishing period, deletion of urea had no effect on animal performance (Putman et al., 1969). These workers concluded only 8—9% crude pro— 26 27 tein was needed to finish steers from 360 kg to slaughter. Klett gt gt. (1973) found no differences in performance of steers from 385 kg to slaughter when dietary crude protein was reduced from 11.5 to 9.0%. Young (1978) studied the effects of withdrawing supplementary protein from Holstein steers at weights of 318, 386 and 454 kg, receiving either a 40 or 80% corn diet. Protein withdrawal resulted in a dietary crude protein level of approximately 8.7% and had no effect on rate of gain or feed efficiency for either of the diets at any of the weights. Conflicting results have been reported by Greathouse t l. (1974), who reported decreases in daily gain and feed efficiency when crude pro- tein was reduced from 11.8 to 9.5% on all sorghum grain diets, and Dartt gt gt. (1976) who observed protein with— drawal from corn—corn silage—soybean meal diets after the 84th day of a 168 day finishing trial resulted in decreased average daily gain and increased TDN required per pound of gain. Crude protein in this trial was reduced to 7.6%. In most instances, carcass merit was not effected by protein withdrawal (Young, 1978; Klett gt gt., 1973; Peter— son, gt gt., 1973; Winchester gt gt., 1957). Greathouse gt gt. (1974) reported carcasses from steers fed low protein diets had smaller rib eye area and lower quality grade. Dartt gt gt. (1978) observed decreases in rib eye area and fat over the rib but no change in marbling or quality grade when protein was withdrawn from Hereford x Angus steers dur— ing the last half of a 168 day feeding trial. 28 B. Level of Nitrogen Intake Effects on Rumen Metabolism and Microbial Protein Synthesis Consistent decreases in the concentration of rumen ammonia have been recorded when the levels of nitrogen and crude protein in the diet are decreased (Smith gt gt., 1980; Crickenberger gt gt., 1979; Leibolz and Hatman, 1972). When supplemental protein was withdrawn from Holstein steers the rumen ammonia level prior to feeding fell to 4.6 mg/100 ml of rumen fluid (Young, 1978). In a further study, Young (1978) measured rumen ammonia concentration at 0, l, 4 and 6 hours post—feeding in heifers fed either 12.9 or 9.4% crude protein (CP) in the diet. Ammonia levels were lower in the low protein diet at all sampling times and were higher than the 5 mg/100 ml level determined necessary for maximal microbial growth by Satter and Slyter (1974) at only 1 and 4 hours post-feeding. Satter and Slyter (1974) reported that increasing the rumen ammonia concentration above 50 mg/liter of rumen fluid with urea had no effect on microbial protein synthesis. Sutton gt gt. (1975) observed no difference in the quantity of microbial protein synthesized per kilogram of organic matter digested when sheep were fed an unsupplemented ration with 8.9% CP versus a protein supplemented ration with 12.3% CF. In steers, low quality roughage rations supplemented with urea to 8.5% CP synthesized 17.9 g of microbial pro— tein/100 g of organic matter (OM) digested compared to 19.9 29 g/100 g of OM with urea supplementation to 10.8% CF, 19.3 g/100 g OM digested with soybean meal supplementation to 11.1% CF (Kropp gt gt., 1977). These workers also noted a decrease in bypass protein on the low level of urea supple- mentation. Increases in nitrogen intake from 2 to 4 to 9 g/day resulted in linear increases in production of micro— bial protein in sheep ranging from 32.5 to 50.0 g/day (Hume t 1., 1970) while nitrogen intakes of 16 g/day showed no further increase beyond the 9 g/day intake. Pilgrim gt gt. (1970) infused 15NH4SO4 continuously into the rumen of sheep and measured the concentration of 15N in bacterial-N, —N on high and low nitrogen diets. 3 They found that on low N diets, the proportion of 15N in protozoal—N and rumen NH bacterial—N and protozoal—N represented a higher percentage of the 15N found in rumen NH3-N. They concluded the extent of microbial protein synthesis on the low N diet was more dependent on rumen NH -N as a starting point for synthesis. 3 These workers further observed the extent of conversion of plant—N to microbial—N was 68% for the low—N diet and 54% for the high N diet. This indicates a decrease in the bypass of plant protein on low N diets. Harrop and Phillipson (1974) observed the rumen fluid volume in sheep when nitrogen intake was 11.4 g/day was only 78% of the fluid volume when nitrogen intake was 20.7 g/day. They also found the rate of dilution of the high— N diet to be only 65% of the dilution rate for the low N diet. They attributed this difference to an increase in saliva 30 production. Kropp gt gt. (1977) found no significant differences in digesta passage, dilution rate or rumen turn— over time in steers when low quality roughages were supple— mented with varying levels of urea. Leibholz and Hartmann (1972) recorded a non-significant decrease in the flow of digesta to the duodenum when sheep were fed 1.4 g N/day as compared to 16 g N/day. They also reported decreased flow of total N and ammonia—N to the duodenum on the low-N diet. Hume gt gt. (1970) observed the amount of nitrogen flowing out of the rumen of sheep exceeded the nitrogen intake when intakes were 2 g N/day and 4 g N/day. At 9 g N/day intake, the nitrogen flow out of the rumen was approximately equal to intake and at 16 g N/day intake, the nitrogen flow out of the rumen was less than the intake. Flow of nitrogen into the duodenum was similar for hay diets supplemented with Iurea to attain nitrogen intakes of 4.26 and 9.86 g/day (Beever _t _t., 1971). They suggested that further syn— thesis of microbial protein on the higher N diet was limited by a lack of available energy. Crickenberger gt gt. (1979) reported the abomasal flow of nitrogen measured as a percent of the nitrogen intake increased when the crude protein level of corn silage and high grain diets was reduced for growing steers. Mehrez _t gt. (1977) reported the minimal rumen ammonia concentration necessary for the maximal rate of fermentation of barley was 23.5 mg/100 ml of rumen fluid. Phillips and Roberts (1966) reported a higher rate of fermentation of 31 rumen contents when oil and protein supplements were both administered orally as compared with oral oil administration and duodenal protein administration. They suggested that the basal ration crude protein level of 7.4% was too low to support maximal rumen fermentation rate in the presence of supplementary oil. C. Effects of Level of Nitrogen Intake on Digestibility of Ration Components Decreasing the level of nitrogen or crude protein intake generally results in depression of dry matter, organic matter and cellulose digestibilities (Leibholz and Hartmann, 1972; Kropp t 1., 1977; Raleigh and Wallace, 1963). In contrast, Hume _t gt. (1970) observed no change in rate of cellulose digestion nor in the total apparent digestibility of organic matter when nitrogen intakes in sheep increased from 2-16 g/day. Harrop and Phillipson (1974) reported similar tg vitro cellulose digestion rates in sheep given either 11.4 g N/day or 20.7 g N/day. Leibholz and Hartman (1972) and Kropp gt gt. (1977) each observed increases in the ruminal digestion of organic matter and dry matter although total tract digestion of the two parameters decreased when low levels of nitrogen were fed to sheep and cattle, respectively. However, Beever gt a1. (1971) found no change in the site of digestion of energy or cellulose in sheep with different levels of nitro— 32 gen intake. Hume gt gt. (1970) reported similar results when varing levels of urea were added to semi—purified diets for sheep. Greathouse _t gt. (1974) recorded a decrease in crude protein digestibility when the dietary crude protein was reduced from 13.0 to 10.4%. Raleigh and Wallace (1963) reported increases in nitrogen digestibility with each increase in nitrogen level of the diet when low quality hay was supplemented with cottonseed meal or urea to 6.0, 9.0 and 12.0% CF. Nitrogen retention appears to be negatively related to the level of dietary nitrogen (Smith gt gt., 1980; Crickenberger t al., 1979). Smith gt al. (1980) observed that fecal nitrogen was not effected by the level of nitrogen intake but urinary nitrogen increased as the level of crude protein in the diet increased. USE OF MARKERS IN RUMEN PASSAGE AND DIGESTIBILITY STUDIES The ability to determine the composition and quantity of the digesta flowing through the various parts of the ruminant gastro-intestinal (GI) tract is essential in evaluating the value of various feedstuffs and dietary ingredients. The determination of the site of digestion is important since the efficiency of utilization of various nutrients will vary depending on whether they are digested in the reticulorumen by microbial fermentation or digested enzymatically in the lower gut. The extent of digestibility, or absorption, of a nutrient in any section of GI tract can be determined by measuring the difference between the inflow and outflow of the nutrient to and from that particular section of the tract (Faichney, 1975). He discussed the use of indigesti— ble markers for partitioning digestive processes and set the following guidelines for an ideal marker: 1. The marker must be non—absorbable. 2. The marker must not affect or be affected by the GI tract or its microbial population. 3. The marker must be physically similar to or inti— mately associated with the material it is to mark. 4. The method of estimation of the marker in digesta samples must be specific and sensitive and must not 33 34 interfere with other analyses. These markers can also be used to estimate the time available for the digestion of a nutrient. The time of retention and rate of digestion are essential factors in determining the extent to which a nutrient is digested in a particular section of the GI tract. Bull _t gt. (1979) discussed the time available for digestion in the rumen in terms of rumen turnover rate (reciprocal of feeding rate) and rumen dilution rate (feed— ing rate per day divided by 24 hours). They summarized literature indicating a shift in rumen fermentation toward more acetate, butyrate and methane and less propionate when the rate of ruminal turnover was increased. Evans (1981a) discussed the need for determining separate turnover rates for the liquid and solid phases of the rumen. She deter— mined the liquid turnover rate to be higher than the solid turnover rate due to a greater volume of water ingestion as compared to solid feed ingestion plus an increase in liquid volume due to additional salivary secretion. Evans (1981a) concluded feed intake to be the major dietary factor affect— ing liquid turnover, assuming the increased intake was asso— ciated with increased voluntary water intake. In addition, she summized the decrease in liquid turnover rate associated with increased level of grain in the diet to be due to a decrease in the secretion of saliva. Bull gt gt. (1979) also reported the addition of coarse fiber or osmotically 35 active agents to the diet increased the liquid turnover rate. Owens gt gt. (1979) reported an increase in the rumen solid turnover rate in cattle when the level of feed intake increased. However, this response was not apparent when diet changes accompanied the changes in intake (McAllan and Smith, 1976). Energy content of the diet, when included in regression equations with a term for feed intake, had a negative relationship to solid turnover rate (Evans, 1981b). However, these equations were derived from experiments in which the caloric density of the diet was altered by adjust- ing the level of roughage in the diet and not by adding sup— plemental dietary fats. Alterations in the rumen microbial population may also affect solid turnover rates. Faichney and Griffiths (1978) reported decreases in solid turnover rate in sheep fed concentrate diets when they had no rumen protozoa in comparison to sheep with rumen protozoa. Faichney (1980) discussed the importance of using two markers, one for the liquid phase and one for the solid phase, when estimating digesta flow from the rumen. Water Soluble markers such as polyethylene glycol (PEG), Chromium-EDTA and Cobalt-EDTA are often used to mark the liquid phase of the digesta although none of the three meet the requirements of an ideal marker. The primary problems with these markers appear to be some association with the solid phase as well as some absorption from the rumen (Isi- 36 chei, 1980). The result of these deviations from the ideal result in an overestimation of the rumen dilution rate, with PEG, Co-EDTA and Cr-EDTA giving the highest, intermediate and lowest turnover rates, respectively. Lignin, chromic oxide, indigestible ADF and rare earth metals such as ytterbium, lanthinum and ruthenium are indi- gestible markers used to mark the solid phase of digesta. Cr203 has been used for several years as a digesta marker although it moves through the GI tract independent of either the solid or liquid phase (Faichney, 1975). Crickenberger t l. (1979) reported much more highly variable abomasal passage data when using Cr as compared to lignin as an 203 indigestible marker. Lignin also deviates from ideal marker status in that it appears to be partially digested in the rumen (MacRae, 1975), thus overestimating flow from the rumen. Problems also existed in the laboratory analysis of lignin in abomasal digesta (Isichei, 1980). Teeter gt gt. (1981) reported success in the use of ytterbium bound to the feedstuff as a marker of the solid phase. They found differences in the binding affinity of different feedstuffs to Yb and suggested washing of the marked feed to remove unbound Yb. They further reported decreases in the digesti— bility of feedstuffs saturated with Yb indicating the sta— bility of the binding to digestive processes in the rumen. Estimates of the microbial contribution to the composi- tion of post—ruminal digesta can be obtained by the use of 37 microbial markers. In the past, commonly used microbial markers have included RNA, DNA, diaminopimelic acid (DAP) and radioisotopes of sulfur, phosphorous and nitrogen. There are several problems involved with these markers including cost, presence in non-microbial protein sources and variability in marker concentration among animals and at different times post—feeding. Garrett gt gt. (1981) dis— cussed D-alanine as a bacteria marker since it occurs only in bacterial cell walls and suggested a method for its analysis. They found D—alanine to be superior to DAP in that it had a lower coefficient of variation when used in a ratio with bacterial nitrogen. However, they still found variation in the bacterial N to D—alanine ratio when dif— ferent diets were fed and thus recommended separate N to D— alanine ratios be determined for bacteria for each dietary treatment. LITERATURE SUMMARY The inclusion of supplemental tallow in beef rations at levels up to 5% of the ration dry matter generally results in an increase in feed efficiency and an increase in the caloric density of the diet. The primary deleterious effects of feeding tallow to ruminants at levels above 5% of the ration dry matter are depression of dry matter intake and suppression of fiber digestibility. The causes of these effects are not clearly established. As the caloric density of the diet is increased, a decrease in the dry matter intake would be expected to allow for a constant energy intake. However, addition of high levels of tallow depresses the total energy intake below these expected lev— els. Furthermore, increases in the rate of rumen digesta passage and decreases in dry matter digestibility are not normally associated with decreases in voluntary feed intake. These atypical responses indicate an unidentified control on voluntary intake of high tallow diets. It is therefore evi— dent that more extensive research is needed to determine the causes of these negative effects of tallow supplementation on nutrient intake and digestibility, especially when tallow is added to high concentrate diets. Supplemental protein can be withdrawn from high concen— trate diets during the terminal finishing phase without deleterious effects to performance or carcass characteris— tics. However, decreasing the crude protein level to below 38 39 8 or 9% or withdrawing supplemental protein from light— weight, growing cattle will result in decreased gain and feed efficiency. Most literature reports indicate no effect of protein withdrawal on carcass characteristics. Both the addition of supplemental tallow to high con— centrate finishing rations and the withdrawal of supplemen- tal protein from these rations have met with varying degrees of success. As yet, the capability of the simultaneous use of these two dietary manipulations to force finish large framed steers in a shorter period of time has not been esta— blished. It would appear this capability is dependent on feeding tallow at a level which would optimize metabolizable energy intake while feeding protein at levels high enough to maintain maximum rates of rumen fermentation. SECTION I EFFECTS ON FEEDLOT PERFORMANCE AND CARCASS CHARACTERISTICS INTRODUCTION Large framed, European breed cattle have become increasingly popular as feeder calves in U.S. feedlots. However, the extra time on feed required by this type of cattle to attain a desirable degree of finish causes a dramatic increase in the non—feed costs associated with pro- duction. The development of a feeding regime which would reduce the time required on feed and change the pattern of fattening to a more rapid deposition of intramuscular fat would therefore be profitable. Withdrawal of supplemental protein during the terminal finishing phase of the feedlot period while simultaneously increasing the energy density of the diet, via addition of supplemental tallow, could possibly produce such an effect. McCartor and Smith (1978) reported increases in gain, feed efficiency, marbling scores and USDA quality grade when high levels of protected tallow were added to diets fed to steers for 56 days following pasture feeding. This project was designed to evaluate the effectiveness of a high tallow, low protein feeding regime for "force— finishing" large framed steers. If successful, this system would allow the beef industry to take advantage of the abil— 40 41 ity of large framed cattle to grow rapidly and efficiently at lighter weights, yet still market a consumer acceptable product at a young age and a moderate carcass weight. MATERIALS AND METHODS TRIAL 1. Thirty-eight steers were randomly allotted to two dietary treatments with two replicate pens of eight steers per pen and an initial kill group of six steers. The steers appeared to be approximately 50% Simmental breeding. The cattle had been pre—fed for six weeks to attain the desired mean initial weight of approximately 140 kg less than their predicted ideal carcass endpoint. All weights were obtained after withholding feed and water for 12 hours. On day 43 of the test period one—half of the steers from each pen were slaughtered and carcass data obtained. The remainder of the cattle were terminated from the experiment, slaughtered and carcass data obtained after 78 days on feed. During the experiment the steers received either the negative control (NC) ration or the five percent tallow (5%T) ration described in Table 1—1. The 9—10—11 rib section was removed from the carcasses according to Hankins and Howe (1945). The specific gravity of this cut was obtained by weighing in air and then under water at 4°C and percent carcass fat determined according to Kraybill _t gt. (1952). The 9-10—11 rib section was boned and then ground to obtain a representative sample of the soft tissue. These samples were frozen and stored for chem— ical analysis. 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Hume 31 31. (1970) reported a net gain in the amount of N leaving the rumen when low nitrogen diets were fed to sheep and attributed this to recycling of N to the rumen. Crickenberger 33 31. (1979) noted a similar decline in the percentage of the N intake passing to the abomasum as NAN when the level of protein increased in the diet. These workers found higher net ruminal N losses than were observed in this study, but they were working with higher protein levels in the diets. NAN recoveries in this trial are in the range of values reported by ¢rskov 31 31. (1971) with barley-soybean meal rations and Kropp 31 31. (1977) with soybean meal supplemented roughage diets. Tal— low supplementation did not effect the passage of NAN to the duodenum in this trial. Analysis of the undegraded feed N (bypass N) data revealed a tallow x protein interaction. The NT—HP diet resulted in the lowest rumen bypass of N reflecting a higher degree of microbial activity. However, when tallow was added to the HP diet, passage of undegraded protein increased indicating a decrease in rumen protein degrada— tion. Pilgrim 31 31. (1970) reported results which contrast this trial. They found the bypass of plant protein to be lower when low N diets were fed. However, the primary source of protein for the LP diets in this trial would be from zein in the corn which has low rumen degradability Hume, 1970). Thus, the increased bypass on the LP diets in 78 this trial seems logical. Microbial crude protein (MCP) flow to the duodenum (Table 2-7) was higher (P<.01) for HP diets than for LP diets and lower (P<.05) for the T diets than for NT diets. The protein effect is consistent with the previously dis- cussed effects of protein supplementation on DM digestibil— ity and rumen ammonia concentrations and would further indi— cate a higher degree of rumen fermentation on the HP diets. These data are in agreement with Hume 31 31. (1971) but con— trast with Sutton g1 31. (1975) who reported no change in the quantity of MCP synthesized when sheep were fed concen- trate rations supplemented to 12.3% CP versus 8.5% CP unsup- plemented rations. D—alanine is reportedly found only in bacterial cell walls and was used in this trial as an indicator of micro— bial N in the duodenum (Garrett 33 31., 1981). There were trends for the D—alanine concentration in the bacteria to be low and for the bacterial N to D—alanine ratio to be higher in the high tallow rations. Hypothetically, this could be due to an increase in bacterial cell size which would result in a lower proportion of cell walls in the bacteria and therefore less D—alanine in relation to the cell nitrogen. This matter is worthy of future investigation. Organic matter intake, OM flow and OM digestion data are presented in Table 2-7. 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