”waste MIMI/71W77/7/7791?)W “@2311 State ”Shea-guy This is to certify that the thesis entitled ENDOCRINE-GENETIC RELATIONSHIPS IN HOLSTEIN HEIFER CALVES presented by Barbara L. Irion has been accepted towards fulfillment of the requirements for Masters degree in Animal Science 5624/de [ax—"7 Major professor Date /0’ 7’9; 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution RETURNING MATERIALS: IV1ESI.J Piace in book drop to [JBRARJES remove this checkout from .—__ your record. FINES win be charged if book is returned after the date stamped below. W #56?» ENDOCRINE-GENETIC RELATIONSHIPS IN HOLSTEIN HEIFER CALVES By Barbara L. Irion A THESIS Submitted to Michigan State University in partia] fuifiTTment of the requirements for the degree of MASTER OF SCIENCE Department of Animal Science 1982 ABSTRACT ENDOCRINE-GENETIC RELATIONSHIPS IN HOLSTEIN HEIFER CALVES By Barbara L. Irion- The abi1ity to identify genetica11y superior heifers at an ear1y age wou1d be a great asset to the dairy industry. In this thesis are resu1ts of an experiment designed to describe: 1) re1ationships among endocrine traits measured ear1y in Tife and economica11y important traits expressed Tater, and; 2) changes in secretion of certain metabo1ic hormones with age. Twenty Ho1stein heifers, born between January 1977 and March 1979, were in each of two groups differing 640 kg for sire's Predicted Difference for miTk and out of dams produced by a se1ected breeding regimen over 11 years. Anima1s were fed between 0600 and 0730 h dai1y. When heifers were 1,3,5 and 8 months of age, b100d was co11ected at 15 minute intervaTs between 1000 and 1300 hours. A11 sera were assayed for insu1in and growth hormone. Concentrations of tota1 g1ucocorticoids were determined in sera co11ected at 1000, 1130, and 1300 h. Differences due to genetic groups were not significant, but there were changes in concentrations of these hormones due to age. GTucocorticoids averaged 5.0 ng/mT at 1 month and increased to 7.9, 11.0 and 9.2 ng/m1 at 3, 5 and 8 months, respective1y. SimiTarTy, growth hormone increased with age from 7.7 ng/m1 at 1 month to 9.1, 9.8 and 9.4 ng/m1 at 3, 5 and 8 months. In Barbara L. Irion contrast, concentrations of insu1in were greater at 1 month than at 3, 5 and 8 months (5.6, 1.9, 1.8 and 2.3_ng/m1, respective1y). Insu1in decreased from 11.3 ng/m1 at 1000 h to 1.6 ng/m1 at 1300 h at age 1 month, but remained unchanged throughout the day in heifers at 3, 5 and 8 months. Concentrations of g1ucocorticoids, insu1in and growth hormone in young dairy heifers se1ected for high mi1k production did not differ from concentrations of these hormones in heifers se1ected for Tower 1eve1s of mi1k production. Therefore, these hormones wou1d not be good criteria to se1ect geneticaTTy superior dairy heifers at an ear1y age. To my Mom and Dad ACKNOWLEDGMENTS There are a number of peopTe I wou1d 1ike to thank in conjunction with the comp1etion of this thesis. I wou1d 1ike to eXpress my deep appreciation to Lynn Dzuba for a11 her technica1 assistance in the anima1 aspects of this project. My thanks a1so to Drs. C1yde Anderson and John Gi11 as we11 as Larry Chapin for their he1p in the computer work and statisticaT ana1ysis. I wou1d 1ike to express gratitude to Dr. Bi11 Thomas for his he1p as nutritionaT consu1tant in the formuTation of the diets of my experi- menta1 anima1s. I wish to thank Drs. Werner Bergan, Roy Fogwe11, and Lon McGi11iard for serving on my committee. I express my most sincere gratitude to a11 my peers and fe110w graduate students for their mora1 support and he1p in making this thesis a rea1ity. I'd 1ike to acknow1edge Dr. Vasantha Padmanabhan for her guidance and interest in me both before and during my graduate studies. Last1y, I'd 1ike to thank Dr. Ed Convey, not on1y for a11 the he1p he's given me concerning my thesis, but a1so for being my mentor and friend. ii TABLE OF CONTENTS ACKNOWLEDGMENTS LIST OF TABLES ....................... LIST OF FIGURES ...................... LIST OF ABBREVIATIONS ..... . ............. INTRODUCTION . . . . . . . . ............... REVIEw 0F LITERATURE ................... Endocrine Metabo1ism ......... ' ........ Insu1in ..................... G1ucagon ..................... Growth Hormone .................. G1ucocorticoids ................. Factors Contro11ing Endocrine Re1ease ......... Insu1in ..................... G1ucagon ..................... Growth Hormone .................. G1ucocorticoids ................. Changes in the Contro1 of Endocrine Metabo1ism Associated with Aging and Growth ........... Insu1in ..................... Growth Hormone .................. G1ucocorticoids ................. Endocrino1ogy of Genetica11y Different Anima1s Insu1in ..................... Growth Hormone .................. G1ucocorticoids ................. MATERIALS AND METHODS ................... vi vii Ommu \l mount» 0.) (.0 11 11 12 13 13 14 16 17 AnimaTS ...................... Feeding, Caring and Housing of Experimenta1 Anima1s .................... BTood CoTTection Procedures ............ Hormone Assays .................. Statistica1 Ana1ysis ............... RESULTS .......................... Feed Tria1 ....................... Growth Ana1ysis .................... Insu1in ........................ Growth Hormone ..................... G1ucocorticoids .................... DISCUSSION ......................... SUMMARY AND CONCLUSIONS .................. LIST OF REFERENCES ..................... iv LIST OF TABLES Tab1e 1. Summary of Hormona1 Effects on Metabo1ism in Various Tissues ............... .. 10 Tab1e 2. Feed Tria1 Data, comparing "Best" and "Worst" heifers for tota1 gain, average dai1y gain, average dai1y intake and feed efficiency . . . 24 Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. LIST OF FIGURES Body weight gain of "Best" and "Worst" heifers measured monthTy from one to 12 months Insu1in concentrations in serum of "Best" heifers in a month by time interaction ..... Insu1in concentrations in serum of "Worst" heifers in a month by time interaction ..... Growth Hormone concentrations in serum of "Best" and "Worst" heifers by month ...... Tota1 gTucocorticoid concentrations in serum of "Best" and "Worst" heifers by month ..... vi 25 28 30 33 35 ACTH ADG ANOVA CNS DNA FFA GH GLM GnRH k9 MABC MCR ME NEFA NRC RIA SAS TRH ABBREVIATIONS adrenocorticotropic hormone average dai1y gain ana1ysis of variance "best" centra1 nervous system deoxyribonucTeic acid free fatty acids unit gravity growth hormone Genera1 Linear Mode1 gonadotropin re1easing hormone ki1ogram Michigan Anima1 Breeders Cooperative metabo1ic c1earance rate mature equivaTent non-esterified fatty acid Nationa1 Research Counci1 radioimmunoassay Statistica1 Ana1ysis System thyrotrOpin re1easing hormone ”worst" vii INTRODUCTION As the popu1ation of the wor1d increases, the need for economica11y produced, high1y nutritious food becomes more acute. Mi1k and dairy products are good sources of nutrients, but they are not uti1ized to the extent they might, 1arge1y due to high costs of production. One method for 1owering costs is to identify anima1s, at an ear1y age, that are genetica11y superior for mi1k production. E1iminating genetica11y inferior anima1s at a young age wou1d decrease costs of rep1acements. In addition, ova from genetica11y superior animaTS, coTTected ear1ier, cou1d decrease the generation intervaT through embryo transfer and therefore increase the rate of genetic progress. Mi1k production and growth have been shown to be heritabTe traits and great genetic advances in potentia1 for'mi1k production and growth have been made through the se1ection of superior sires and the use of artificia1 insemination. Many physio1ogica1 processes, inc1uding 1actation and growth are regu1ated by the endocrine system, especia11y the metabo1ic hormones. It seems reasonab1e to examine whether or not concentrations of metabo1ic hormones may be an index Of genetic merit for traits of economic importance. At present, it is not known whether hormonaT concentrations measured at an ear1y age have va1ue in predicting an individua1's genetic potentia1 for mi1k production. In this thesis, I asked two questions. First, do concentrations in insu1in, growth hormone and tota1 g1ucocorticoids in b1ood vary re1ative to genetic abiTity of heifers to produce mi1k? Second, how do concentrations of these hormones change with increasing age from birth to eight months? LITERATURE REVIEW ENDOCRINE METABOLISM Ruminant anima1s digest ce11u1ose via microbia1 fermentation in the rumen. Major products of ce11u1ose digestion are vo1ati1e fatty acids, inc1uding acetate, propionate and butyrate. Ba11ard,_;t._l. (1969) and Trenk1e (1971a) found acetate, rather than gTucose to be the major substrate for energy metabo1ism in most peripheraT tissues of ruminant anima1$ after weaning. However, Lindsay (1975) demonstrated that gTucose is the principTe source of energy for the centra1 nervous system in ruminant as we11 as non-ruminant anima1s. 0n1y sma11 quantities of gTucose are absorbed by the gut of ruminant animaTs and therefore g1ucose must be synthesized via gTuconeogenesis. Substrates for gTuco- negenesis inc1ude propionic acid, amino acids, 1actate and g1ycero1 (Ba11are, et a1., 1969; Armstron, 1965; Bergman, et a1., 1966; and t a1. (1966) and Leng, et 31, (1967) dem- Trenk1e, 1978). Bergman, onstrated that propionic acid is a major precursor for 91ucose and may) be sutbstrate for 50 percent of the gTucose produced in the 1iver. According to Judson and Lang (1973a, 1973b), specific hormone changes he1p to maximize g1ucose production from propionate via g1uconeogenesis in ruminant anima1s, thus conserving amino acids for synthesis of protein. Insu1in Because gTucose is required by the centra1 nervous system, its rn regu1ation is important in ruminant as we11 as non-ruminant animaTS. Since insu1in is an important regu1ator of g1ucose production through g1uconeogenesis, it is essentia1 in maintaining homeostasis. Insu1in is a po1ypeptide hormone produced and secreted by the beta-ce11s in the isTets of Langerhan.. Reid, gt__l, (1963) and Jarrett, £3.21, (1972) found that insu1in deficiency, brought about by either pancreatectomy or the diabetogenic agent a11oxan, wi11 cause a diabetic condition in ruminants. This 1eads to impaired uti1ization of g1ucose, acetate and beta-hydroxybutyric acid and a1so causes ketoacidosis and death (Reid, _t_a_1_., 1963; Jarrett, 32331., 1972). Acetate is the princip1e source of energy for periphera1 tissue in ruminant animaTS. Effective uti1ization of acetate is dependent on the stimiTatory effects of insu1in and gTucose (Ba11ard, 1972; Skarda and Bartos, 1969, and Yang, gt_gl,, 1973). Ba11ard (1972), Yang and Ba1dwin (1973), and Mears and Mende1 (1974) have shown that insu1in stimuTates uti1ization Of both gTucose and acetate by adipose tissue. Horn and co-workers (1977) suggested that insu1in may reduce breakdown of muscTe protein rather than affect uptake of amino acids. This hypothesis has been disputed by Trenk1e (1978), who suggested that insu1in inhibits 1ipoTysis and proteo1ysis and stimuTates uptake and incorporation of amino acids into ce11s. i Prior and Christensen (1978) and West and Passey (1967) reported that insu1in inhibits g1uconeogenesis and secretion of g1ucose by the 1iver. It is 1ike1y then, that the high concentrations of insu1in that occur after feeding minimize g1ucose production from propionate and amino acids in the 1iver. However, during the post-prandia1 period, g1uconeo- genesis and hepatic g1ucose output are increased (Katz and Bergman, .4 I. 1") BY | (41’ ) u“) (f l (T) In 1969; Thompson, t 1., 1978), suggesting that the effects of insu1in are offset by other regu1atory hormones or substrate avai1abi1ity. G1ucagon In ruminant as we11 as non-ruminant anima1s, g1ucagon is probabTy the major hormone counteracting the effects of insu1in on metabo1ism of g1ucose in the 1iver. GTucagon is a po1ypeptide hormone produced and secreted by the pancreatic a1pha-ce115 in the is1ets of Langerhan. According to Trenk1e (1978), g1ucagon favors hepatic uptake of propionate. g1ucogenic amino acids and 1actate. G1ucagon a1so stimu1ates g1ycogeno1ysis, adipose tissue trig1yceride breakdown and g1uconeogenesis, thereby main- taining hepatic secretion of g1ucose (Bassett, 1978; Brockman, t a1., 1975b). Growth Hormone Other hormones that are invo1ved in metaboTism inc1ude catacho1amines, gTucocorticoids, thyroid hormones and growth hormone (GH). Of these, on1y secretions of GH appear to f1uctuate with diets varying in energy ba1ance. Concentrations of GH in serum of fasted anima1s or those fed 1imited amounts of feed tend to be 1ower than in animaTs fed ag_1ibitum, suggesting that GH may p1ay a ro1e in mobi1izing fat for energy (Carstairs, 1978). Bassett (1971, 1974b), Hove and B1om (1973), and 810m, §t_al, (1976) found concentrations of GH in serum to be negativeTy corre1ated with feed intake and insu1in concentrations. However, Herte1endy and Kipnis (1973) observed a positive re1ationship between concentrations of GH and free fatty acid (FFA) in serum. This positive association with FFA suggests that GH may be invo1ved with antagonism of g1ucose uti1ization .FJ. Du and promotion of 1ip01ysis (Bassett, 1978). Growth hormone has been shown to exhibit anti-insu1in 1ike effects (Baughaday, §__aa1. 1975), and therefore cou1d be considered catabo1ic in regard to adipose tissue. Growth hormone may p1ay an important ro1e in musc1e deve1opment by stimu1ating mitosis of sate11ite ceTTS. Sate11ite ce11s are mononu- c1eated ceTTS, Tying within the basement membrane of musc1e fibers. As they undergo mitosis, these nuc1ei become incorporated into the musc1e fibers, thereby increasing the amount of DNA avai1ab1e to direct synthesis of protein (Mauro, g___l_.,1970). Post-nata1 increase in DNA content of musc1e is arrested by hypophysectomy, but partia11y restored by exogenous GH, and comp1ete1y restored by exogenous GH p1us thyroid hormone (Trenk1e, 1976). GTucocorticoids Rei11y and BTack (1973), and Rei11y and Ford (1974) found that g1ucocorticoids promote proteo1ysis and increased hepatic uptake of amino acids. This process reduces avai1abi1ity of amino acids to extra- hepatic tissues for protein synthesis, so gTucocorticoids can be considered to be cataboTic. McNatty,e .(1972) observed that g1ucocorticoid concentrations in b1ood are not inf1uenced by eating, but rather fo11ow a circadian rhythm. Mi11s and Jenny (1979) reported that gTucocorticoid concentrations increased during fasting. This increase has been associated with g1ucagon re1ease (Marco,e a1.,1973; wise, §__aa1. 1973, and Bassett, 1975), and coincides with 10w insu1in 1eve1s. Thus, the endocrine ba1ance during starvation favors degradation of musc1e protein, increased uptake of amino acids by the 1iver, and extensive g1uconeogenesis. The net effect is 1055 of ske1eta1 musc1e mass. FACTORS CONTROLLING ENDOCRINE RELEASE Insu1in Bassett (1974a, 1975) and Trenk1e (1970c) both reported that insu1in concentrations increase in serum after eating in ruminant animaTS. Lofgren and Warner (1972) and Ross and Kitts (1973) observed the insu1in increase to be more pronounced in animaTS fed hay than those fed concen- trates. Bassett, gt_al, (1971) and Horino, gt_§l, (1968) found insu1in concentrations in serum of sheep to be positive1y re1ated to the intake of digestab1e organic matter and protein. The amount of food ingested seeming1y inf1uences the magnitude of serum insu1in concentrations attained after feeding. However, Bassett (1975) hypothesized that the composition of the feed has 1itt1e direct inf1uence on the insu1in re- sponse except through rates of digestion or amounts of nutrients absorbed. Intravenous injections of FFA, butyrate and propionate stimu1ate insu1in secretion in fasted sheep (McAtee and Trenk1e, 1971b; Trenk1e, 1970c). But, it is not c1ear how these fatty acids participate in contro1 of secretion under physioTogica1 conditions (Trenk1e, 1978; Bassett, 1975). 'McAtee and Trenk1e (1971a), Herte1endy and Kipnis (1973), and Davis (1972) a11 reported that intravenous injections of amino acids in amounts resu1ting in super-physioTogicaT concentrations of amino acids in the b1ood increased insu1in in p1asma. But concentrations of amino acids that are norma11y found in p1asma after feeding do not significant1y a1ter insu1in secretion (Bassett, 1975). Trenk1e (1978) observed a biphasic change in secretion of insu1in in response to feeding. The first increase occurs within one hour post- prandia11y, and the second peaks four to six hours Tater. A1though the mechanism by which feeding increases insu1in is not known, it has been hypothesized that the first insu1in re1ease is due to a re1ease of I choTecystokinin-pancreozmin and secretion, resu1ting from feed passage into the rumen (Bassett, 1974a; Trenk1e, 1972). The second increase may be due to absorbtion of short-chain fatty acids from the rumen as we11 as absorbtion of g1uconeogenic precursors from the digestive tract (Trenk1e, 1978). I A1though insu1in is the major regu1ator of gTucose turnover rates, concentrations of g1ucose in p1asma may not be an important determinant of insu1in secretion in ruminant anima1s (Chase, _t_al,, 1977; Bhattacharya and A1u1a, 1975; Bassett, 1975; Trend1e, 1978). A definitive statement regarding the mechanism of insu1in secretion in ruminant animaTS can not be made at this time. GTucagon G1ucagon secretion is stimu1ated by hypog1ycemia, catachoTamineS (Bassett, 1972; Brockman and Bergman, 1975a), and g1ucocorticoids (Driver and Forbes, 1978; Wise, gt _l., 1978). There is a postprandia1 increase in g1ucagon, coinciding with increase gTuconeogenic output of g1ucose from the 1iver. Bassett (1975) has hypothesized that the ratio of insu1in to gTucagon is important in 91ucose regu1ation, but evidence supporting this view must be considered pre1iminary. Growth Hormone Growth hormone concentrations f1uctuate great1y in serum of ruminant anima1s, i.e. it is episodic (Bassett, 1974b; Hove and B1om, 1973; McAtee and Trenk1e, 1971b). Manns and Boda (1967) Observed that fasting does 1m ri- -—-4 Cr not cause an increase in mean concentrations of GH in sheep, but both the amp1itude and frequency of the episodic surges are greatest during this time (Bassett, 1974b; Wa11ace and Bassett, 1970; McAtee and Trenk1e, 1971b; Driver and Forbes, 1978). In sheep, GH concentrations decrease in p1asma after eating, and both the frequency and amp1itude of the episodic secre- tions are decreased for two to four hours (Trenk1e, 1967, 1978; Bassett, 1974b, 1975, 1978; Driver and Forbes, 1978). Bassett (1974a) reported that growth hormone concentrations tend to be Tower in serum of sheep fed 1arge quantities of food, and the effects of feeding re1ative to time of feeding are more difficuTt to resoTve than in sheep fed 1imited quantities. Hove and B1om (1973) Observations with cattTe were consistant with those of Bassett's (1974a) findings in sheep. Secretion of GH is re1ated inverse1y to avai1abi1ity of nutrients. Increased concentrations of growth hormone wou1d seem to increase mobi1ization Of energy from adipose tissue to satisfy metabo1ic requirements. GTucocorticoids The concentrations of gTucocorticoids in b1ood change in response to fasting (Mi11s and Jenny, 1979; Trenk1e, 1978), but not in response to feeding (Bassett, 1974b, 1975; Trenk1e, 1978; Grigsby, §t_gl,, 1973). This may be due to the fact that g1ucocorticoids increase when an anima1 is stressed. Thus, the increase in gTucocorticoids due to fasting may be a resu1t of stress. Evidence for the mechanism of secretion and regu1ation is not c1ear at this time. The effects of some metabo1ic hormones are summarized in Tab1e 1. 224.11% CthIJx _: .23.. FCAEJCE :C vgtcxkk -.:C:>.CI .~ my :.:\K. 10 .mpmevcm “cmcwsacuco: Av cw awsmcovpmpmc m>wpmmmz .222; 22.55.. 9 :? awcmcoquch m>wuwmom .mpmswcm acmcwszgucoc cw awcmcovumpmg m>wpwmoa.nv mpmewcm uzmc_szc Av cw awsmcowpmpmg m>wummmz cowumu Tacoma :wmuoca mmmmpmm << oxmua: .0 Illlll mwmmcmm Tooxpo mwmapo -cmmooxpo commo:_w .couoozpw mcosgo: cpzocm :__:m:H mcosco: Lw>wo vo Emeonmumz co muommvm PacoeLo: mwmmguczm camouxpw fl “commcmch mmou=Fw commozpw .cououzpo mcosco: cgzccu c_F:mcH mcoELo: mpomzz we Emvponmumz co mpuwvvm chosgo: O .0 Av .av Av xv Av Av Av Av Av Av Av Iv. Av . mwmmcmm mvmmcmmoawo m_mm:mmouwx -omcoozpu Av Av .31 Av Av .av Av .av Av Av fl Av Av Av Av mwmmsucmm “commence mwmap grapes; << nocmmooxpw Av Av D. -0 -0 Av AV _Av .I. Av Av .4. Av Av IIIII IIIIIII 1 IIIIIIIIII mmeESEAm coLBeuvacvmu amouzpu evapoca -ac 0.10) for ca1ves in the two genetic groups (Tab1e 2). Tota1 weight gained during this feeding tria1 ranged from 13.9 to 38.6 kg with a mean of 25.3 kg for a11 animaTs. Average dai1y gain and average dai1y intake were 0.83 kg/day and 3.2 kg/day, respective1y. Feed efficiency, defined as the ratio of kg of gain to kg of feed was higher (P<0.06) in ca1ves from the "Best" group than for those of the “Worst" group. Growth Ana1ysis Body weight was not different (P>0.10) due to genetic groups unti1 9 months of age (Figure 1). From 9 to 12 months, ca1ves from the "Best" group were heavier (P<0.05) than those in the "Worst" group. There were no differences (P>0.10) due to genetic group in the height‘ of the withers at any of the ages examined. Insu1in When averaged over month and time within months, concentrations of insu1in were not different (P>0.10) in serum of ca1ves in the "Best" and "Worst" genetic groups. Mean va1ues were 2.8 :_1.2 and 3.1 :_1.2 ng/m1, respective1y. However, concentrations of insu1in in serum did change with age (Figures 2 and 3). Insu1in concentrations averaged 23 24 Tab1e 2. Body weight and feed intake of heifers in "Best" and "Worst" genetic groups. ‘ Tota1 Average dai1y Average dai1y % feed b gain gain (kg/day) feed intake efficiency (kg) (kg/day) Best 26.1 .87 3.2 29.0 Worst 24.7 .81 3.1 26.2 Range .13.9:38.6 .044-1.26 2.1-4.8 14.4-35.6 AnimaTS in "Best” group were more feed efficient (P<0.06) than those of the "Worst" group. b Feed efficiency = ggéfi- x 100 25 Figure 1. Body weight gain of "Best" and Worst" heifers measured month1y from one to 12 months. 300 250 52‘ 200 '— 8 6 ISO 3 >. o O 100 c0 50 O H BEST O--O WORST lLlllllJl Ill |234567891011|2 AGE (months) Figure 2. 27 Insu1in concentrations in serum of "Best" heifers in a month by time interaction. Standard errors ca1cu1ated from poo1ed mean square error for comparisons 1) between genetic groups = :_.4 ng/m1, 2) between months = i 1.1 ng/m1 and 3) among times within months = :_.5 ng/m1. I4 13 :12 in 510 29 3 0:8 LIJ m7 Z6 .2. _,5 84 Z -3 2 l o ”BEST” o—o M01 O—O M03 A—A M05 A—AMOB R a f‘ A A A“! ‘ " A ‘ “Anya-.24, - ‘"+v v ‘n . . ' ,. 1111111111111 1000 1030 1100 1130. 1200 1230 1300 TIME 29 Figure 3. Insu1in concentrations in serum of "Worst" heifers in a month by time interaction. Standard errors ca1cu1ated from a poo1ed mean square error for comparisons 1) between genetic groups = :_.4 ng/m1; 2) between months + 1.1 ng/m1 and; 3) among times within months = :_.5 hg/mT. BZEGE INSULIN IN SERUM (ng/mI) O—wammflmm "WORST" HMOT CF43 MONS .AFHA NKD5 HMOB A A A 11“ A. A ‘1 _" nn_n “._I\r\ \fl/ [1111 J L] 1100 1130 1200 1230 I300 THWE 31 over time of day were 5.6 :_.7 ng/m1 at one month of age, then decreased (P<0.01) to 1.9 :_.2, 1.8 :_.1 and 2.3 :_.2 ng/m1 at 3, 5 and 8 months of age, respective1y (Figures 2 and 3). Concentrations of insu1in at one month of age were higher at the start of samp1ing. This peak was f011owed by a decTine during the interva1 from 1000 h to 1300 h. Growth Hormone When averaged over months and time within months, concentrations of GH in serum did not differ (P>0.10) between genetic groups. Averages for "Best" and "Worst" were 8.8 :_2.0 and 9.2 :_1.9 ng/m1, respective1y. However, GH was affected by age, i.e., 1ower (P<0.05) in serum coT1ected at one month than at 3, 5 and 8 months of age (Figure 4). Mean concen- trations were 7.7 :_0.5, 9.1 i 0.7, 9.8 i 0.5 and 9.4 i 0.6 ng/mT at 1, 3, 5 and 8 months of age, respective1y. There was no change (P>0.10) in GH concentrations throughout the four hour samp1ing period at any of the ages examined. G1ucucorticoids Serum tota1 g1ucocorticoid concentrations, when averaged over months and time within months, were not affected by genetic groups. However, g1ucocorticoid 1eve1s did change with age (P<0.05). Mean g1ucocorticoid 1eve1$ were 5.0 :_0.7, 7.9 :_1.3, 11.6 :_1.6 and 9.3 :_0.9 ng/m1 for ages 1, 3 5 and 8 months, respective1y (Figure 5), with serum concentra- tions being higher (P<0.05) at five months of age than at one month. There was no change (P>0.10) in tota1 gTucocorticoid 1eve15 over time of samp1ing within age. 32 Figure 4. Growth hormone concentrations in serum of "Best" and "Worst" heifers by month. Standard errors ca1cu1ated from poo1ed mean square error for comparisons; 1) between genetic groups = :_.62 ng/m1, 2) between months = i_1.6 ng/m1 and; 3) among times across months = 2.3 ng/m1. AmficoEv med. m m m _ d _ Ammo; 01.0 . a mem I \ .1 \\ ?" Hill I “ 111IOI|11 l (CLOVPON—O \ \ \ SH? (IN/5U1WOHBS NI 3NOINEI0H HIMOEIO l 03 II :9 34 Figure 5. Tota1 g1ucocorticoid concentrations in serum of "Best" and "Worst" heifers by month. Standard errors ca1¢u1ated from pooTed mean squared error for comparisons; 1) between genetic groups = i_1.1 ng/m1; 2) between months = :_1.6 ng/m1 and; 3) among times across months = :_8.4 ng/m1. l (Ila/fill) wnaas NI smoouuoooomo “IVLOL H BEST O-O WORST 5 AGE (months) DISCUSSION One objective of this thesis was to determine if re1ationships exist between traits measured in individua1s ear1y in Tife and their breeding va1ue for mi1k yie1d. If anima1s with high breeding va1ue cou1d be identified at an ear1y age, costs of rearing rep1acements cou1d be reduced by e1iminating genetica11y inferior anima1s. For examp1e, if inferior bu11s cou1d be identified and e1iminated at an ear1y age, the costs to maintain them unti1 information regarding their daughters' first 1actation performance became avai1ab1e wou1d aTSo be reduced. Based on data presented, there is no difference in concentrations of insu1in, GH or tota1 gTucocorticoids between the two groups of heifers which were compared. Fai1ure to detect- any differences in these hormones may indicate that the hormones measured are not re1ated to genetic abi1ity to produce mi1k. On the other hand, mi1k producing abi1ity may not be re1ated to a sing1e hormone, but rather a comp1ex interaction among severaT hormones. C1ear1y, other hormones, such as pro1actin, thyroid' hormones, and parathyroid hormones are invoTved in mi1k production and metaboTism which were not studied. Perhaps one or more of them wou1d be a better indicator of a young anima1's potentia1 to produce mi1k. An a1ternative exp1anation for these data is that abso1ute concen- trations of any one hormone in serum may not be as important in regu1at- ing metabo1ism as the response it e1icits from certain tissues. Responses may be regu1ated by changes in receptor concentrations or affinity, or by changes in the amp1ification systems invo1ving cyc1ic nuc1eotides, 36 37 protein kinases or protein gradients. Since no differences in growth were observed between VBest? and "Worst" heifers unti1 nine months of age, perhaps hormonaT differences do not occur unti1 this time a1so. Any such differences wou1d have gone undetected in this study as b1ood samp1ing was discontinued after heifers were eight months of age. Based on 305 ME 2.x 1actationa1 records, heifers in the "Best" group produced 1004 kg more mi1k than those in the "Worst" group, averaging 6994 kg and 5990 kg, respective1y. Seven heifers were cu11ed before their first 1actation records were avai1ab1e; four vo1untari1y and three invoTuntari1y. It is important to keep in mind that the two groups of heifers used in this study were genetica11y different from each other based on an 11 year breeding program uti1izing bu11$ of diverse genetic backgrounds. Neverthe1ess, the possibi1ity remains that differences in mi1k production potentia1 between groups were not sufficient for differences in endocrine measures to be resoTved. Dams of the heifers used in this experiment differed between ”Best" and "Worst” groups in mi1k production by 737 kg. Broster, _t_al, (1969) reported that Ho1stein cows producing 1arge quantities of mi1k wi11 preferentia11y direct energy toward mi1k pro- duction and away from body tissues. The converse is true for Ho1stein cows producing 1esser quantities of mi1k (Broster, t 1., 1969) and for beef cows (Hart, gt al,, 1979). Hart, _t_gl, (1978) a150 observed that Ho1stein cows have higher GH, NEFA, and beta-hydroxybutyrate con- centrations than do beef cows, but beef cows have higher insu1in con- centrations throughout 1actation than do dairy cows. Partition of energy between the mammary g1and and other tissue is based on rate and '38 direction of metaboTism which is regu1ated through endocrine contro1. Perhaps the endocrine differences that exist between dairy and beef cows cause the differences in partition of energy described above. A1ternative1y, endocrine differences may resu1t from metaboTic differences rather than cause them. When eva1uating data of the type reported by Hart, _t_gl, (1978), it is important to keep in mind that dairy and beef cows differ in many ways in addition to differences in abi1ity to produce mi1k. Thus, it is impossib1e to attribute endocrine varia- tion to a singTe characteristic or c1ass of characteristics such as metabo1ism. Fai1ure to detect any hormonaT differences attributabTe to se1ection in these young (1 to 8 month 01d) growing heifers may be exp1ained if important measurab1e endocrine differences occur on1y at the tme of 1actogenesis or 1actation. In support of this view, Hart, _tpgl, (1978) reported that differences in growth hormone and insu1in concentrations in serum were resoTved between beef and dairy cows during 1actation, but not during the dry period. Being ab1e to discern endocrine varia- tions in adu1t 1actating catt1e wou1d not be particu1ar1y usefu1 in se1ection of genetica11y superior mi1k producing anima1s at a young age. The second objective of this thesis was to describe changes in secretion of insu1in, GH and gTucocorticoids in dairy heifers as they age. Concentrations of insu1in in serum of one month 01d ca1ves are higher than at 3, 5 or 8 months. Insu1in concentrations a1so change with time of day at one month of age, but not at any other age examined. This increase at one month may be due to increased re1ease of insu1in in response to feeding. For examp1e, Trenk1e (1978) observed a biphasic increase in insu1in in serum postprandia11y in sheep. The 39 first increase was detected within one h of eating and was thought to be due to re1ease of gastrointestina1 hormones from a neura1 response to the act of eating. The second increase in insu1in occurred four to six h postprandia11y. A simi1ar insu1in response to time post-feeding was observed when ca1ves in the present study were one month 01d, but not at 3, 5 or 8 months. This may be due to a combination of factors. First, these ca1ves were fed at 0600 h unti1 they were two months 01d, and at one month of age, insu1in concentrations in serum were greatest at 1000 h, or approximate1y four h after eating. By three months of age, ca1ves are no 1onger fed mea1s, but rather grouped with animaTs of simi1ar size and fed ag_1ibitum. Feed being avai1ab1e at a11 times wou1d tend to mask insu1in response to mea1 feeding. A150, at one month of age, ca1ves were being fed who1e mi1k which contains 1actose. Lactose is digested in the gut to ga1actose and gTucose, both of which cause an increase in b1ood insu1in. By three months, the diets of these ca1ves did not contain 1actose and there- fore an insu1in response due to digestion of sugars was not expected or observed. The dec1ine in insu1in concentrations after 1000 h at one month of age may be in response to decreased absorbtion of nutrients from the gut. The gradua1 decrease in insu1in cannot be attributed to metabo1ic c1earance fo11owing a sing1e transient re1ease of insu1in because the t13 of insu1in is 1ess than 10 minutes (R. Nachreiner, personaT communication). Concentrations of GH were 1ower in serum of ca1ves at one month of age than at 3, 5 or 8 months. Irvin, and Trenk1e (1971) and Purchas, t a1. (1970) reported that age did not inf1uence GH concentrations in 4O p1asma. However, Trenk1e (1970a) reported that concentrations of GH were greater in serum of eight week 01d Hereford ca1ves than in serum of o1der ca1ves. In addition, Ke11er gt__l, (1979) reported that con- centrations of GH in serum are greater in Hereford ca1ves at one month than at three or seven months of age. Resu1ts of these experiments by Trenk1e (1970) and Ke11er, _t__l, (1979) do not agree with those pre- sented herein. PossibTe exp1anations for these differences are as fo110ws.' Trenk1e (1970) and Ke11er, _t__l. (1979) both samp1ed jugu1ar b1ood via venipuncture once dai1y. Since GH secretion is thought to be episodic, one samp1e wou1d not necessari1y give an accurate account of the hormone concentrations in young ca1ves. A1so, in both experiments, (Trenk1e, 1970; Ke11er, _t__l., 1979), Hereford ca1ves were used. Irvin and Trenk1e (1971) fouhd no evidence to support the view that GH varies between breeds. But those measurements were across beef breeds and crossbred beef breeds on1y i.e., beef and dairy breeds were not compared. Perhaps a difference in CH secretion exists between beef and dairy breeds that has not yet been reported. After the first month, there was no change in concentrations of insu1in or GH associated with aging in this study. Growth hormone is known to exhibit anti-insu1in effects and perhaps the increase in GH seen after one month of age may be re1ated to the decrease in insu1in concentrations found in serum at the same time. The Tower 1eve1s of GH found at one month of age compared to 3, 5 and 8 months may be due to changes in diet or differences in mode of digestion of nutrients associated with onset of rumen function. Lower mean concentrations of GH observed at month one may aTSo be re1ated to heifers being mea1-fed. Whi1e both Trend1e (1967) and Bassett (1974a) observed a decrease in 41 concentrations of GH postprandia11y in sheep, it must be kept in mind that hormone 1eveTs of those experimenta1 anima1s were measured after they were starved for three to five days, then fed. This experimenta1 design wou1d not necessari1y revea1 physioTogica11y norma1 hormone responses to feeding. Anfinson, _t__l, (1975) observed that secretion of growth hormone is episodic. Simi1ari1y, GH secretion in the present study was episodic at a11 ages studied. However, average concentrations of GH did not change with time of day at 1, 3, 5 or 8 months of age. To the author's know1edge, no one has previou1sy described changes in tota1 gTucocorticoid concentrations re1ative to growth and aging of catt1e. G1ucocorticoids maintain b1ood gTucose (Long and Lukens, 1936; Lum1ey and Nice, 1930) and 1iver and musc1e g1ycogen stores by stimu1at- ing production of gTucose via g1uconeogenesis. Ca1ves at one month of age wou1d have 1ess need for gTucose than wou1d oner ca1ves since they are sti11 ingesting mi1k and have no funciona1 rumen. This may exp1ain why concentrations of gTucocorticoids were 1ower in serum c011ected from ca1ves at one month than at 3, 5 or 8 months of age. Higher concentrations of g1ucocorticoids observed at five months are difficu1t to exp1ain. In agreement with Unepresent resu1ts, Leung (1979) observed an increase in g1ucocorticoids with age in dairy ca1ves with a peak observed at approximate1y five months. This increase may be associated with onset of puberty. For examp1e, Desjardins and Hafs (1969) observed a rapid increase in ovarian weight from birth to five months, f011owed by a p1ateau from five to eight months and resumed ovarian growth from 8 to 12 months of age. Since age at onset of puberty in Ho1stein heifers is 8 to 12 months (Morrow, 1968), the p1ateau of 42 ovarian growth observed at five to eight months of age may be an indication of prepuberta1 ovarian deve10pment. A ro1e for adrena1 steroids in puberty has been estab1ished for humans and rats. Ducharme, _t;_l, (1976) hypothesized that, in humans, a prepuberta1 increase in the adrena1 steroids dehydroepiandrosterone, andresteindione and estrone may be responsibTe for the change in gonada1 hormone 1eve1s necessary for the onset of puberta1 deve10pment. In addition C011u and Ducharme (1978) reported that adrena1 steroid secretion increased three to four years prior to onset of puberty in humans. These authors hypothesized that the adrena1 steroids, especia11y a1dosterone, are important in the process of maturation of the hypothaT- amus. The re1ationship they observed between adrena1 and gonada1 steroids is evidence in favor of a ro1e for adrena1 steroids in the maturation of the centra1 nervous system mechanisms which 1ead to puberty. Gorski and Lawton (1973) demonstrated that adrena1ectomy of immature rats at 19 and 25 days of age, but not at 35 days, significantTy de1ayed time of onset of puberty. They a1so found that autotranspTan- tation of the adrena1s at 18 days prevented this de1ay. These data were interpreted as evidence that during a certain period, the adrena1s p1ay a ro1e in maturation of the hypothaTamic-pituitary-gonada1 axis. Per- haps the increase in tota1 g1ucocrticoids we observed in dairy heifers at five months of age is an indication of prepuberaT maturation. A1ternative1y, the increase in g1ucocorticoid concentrations at five months may have been due to management procedures. Ca1ves were group housed by age beginning at three months of age. At approximate1y five months of age, heifers were moved into a pen of oner ca1ves, thereby putting them into a group in which they were the sma11est 43 anima1s. This cou1d have posed a stressfuT situation for the ca1ves, resu1ting in an increase in adrena1 gTucocorticoids. Because a comp1ete understanding of the actions of the g1ucocorticoids is not avai1ab1e at this time, it is not possib1e to exp1ain for certain what significance the changes in these hormones associated with aging may entai1. SUMMARY AND CONCLUSIONS The re1ationship between insu1in, growth hormone and g1ucocorticoid concentrations measured in serum ear1y in 1ife of HoTstein heifers and their genetic potentia1 to produce mi1k was studied. In addition, changes in hormone concentrations with age through eight months was determined. These heifers were the cu1mination of a genetics project begun in 1967 whereby cows in the Michigan State University herd were divided into two groups and arbitrari1y 1abe1ed ”Best" and "Worst". The cows were then bred to sires se1ected on the basis of the first eva1uation of daughters' mi1k yie1d. Predicted differences between mi1k yie1d of . daughters of bu11s in the 10th c1ass (B10 and W10) differed by 600 kg; PD of bu11s from the 11th c1ass (BH and W1]) differed by 820 kg. Dams of these heifers differed between "Best" and "Worst“ groups in mi1k production by 737 kg. Daughters of cows became members of the same group as their dams. First 1actation records of heifers used in this experiment differed between "Best" and "Worst" by 1004 kg of mi1k. During a 30 day feeding tria1 when ca1ves were 60 to 90 days 01d, tota1 weight gained, average dai1y gain and average dai1y feed intake were not different between the genetic groups. Feed efficiency, defined as the ratio of kg of gain over kg of feed, was higher in ca1ves from the "Best" group than for those in the "Worst" group. Heifers were weighed and height of withers recorded month1y unti1 12 months of age. Rate of gain of body weight was not different due to genetic background unti1 9 months of age, after which time ca1ves 44 45 from the "Best? group gained weight faster and were heavier than ca1ves in the "Worst" group. There was no difference between genetic groups in wither heights at any of the ages examined. B100d was co11ected when heifers were 1, 3, 5 and 8 months of age. Concentrations of insu1in, GH and tota1 gTucocorticoids in serum were not different due to genetic background at any of the ages examined. But, there were changes in a11 hormone concentrations attributabTe to aging. At one month of age, insu1in was higher and GH concentrations were 1ower than at other ages. Insu1in concentrations in serum a1so changed with time of day when heifers were one month 01d, i.e., highest at approximate1y 1000 h and dec1ining 1inear1y unti1 1300 hours. The effects of age and/or time of day may be due to a change in the response of the pancreas to feeding. No changes in hormone concentrations throughout the day were observed for GM or g1ucocorticoids at any age, and none for insu1in after one month of age. Tota1 g1ucocorticoid concentrations in serum increased from 5.0 ng/m1 at one month to 11.6 ng/m1 at 5 months, fo11owed by a sTight decrease to 9.3 ng/m1 at 8 months of age. This peak in gTucocorticoid concentrations in serum observed at 5 months of age may be an indication of prepubera1 maturation. We conc1ude that there is no difference in insu1in, GH or tota1 gTucocorticoids in serum of genetica11y diverse groups of dairy heifers when examiined at 1, 3, 5 or 8 months of age. Possib1e exp1anations for fai1ure to see differences inc1ude; 1) hormones different than those measured or ratio of hormone concentrations or hormone/receptor re1a- tionships may be better indices of genetic potentia1; 2) endocrine differences between anima1s se1ected for mi1k production may not exist 46 unti1 1actation begins, and 3) genetic diversity of these heifers was not adequate to detect endocrine differences. Therefore, these methods wi11 not provide a system to identify superior anima1s ear1y in 1ife. Changes observed in insu1in and GH concentrations in serum associated with aging seem to be re1ated to change in diet, time of feeding, and maturation of the digestive system from a monogastric-1ike anima1 to that of a ruminant anima1. Changes in tota1 g1ucocorticoid concentra- tions in serum may be re1ated to genera1 maturity or specifica11y re1ated to processes 1eading to puberty. LIST OF REFERENCES LIST OF REFERENCES Anfinson, M.S., S.L. Davis, E. Christian and 0.0. 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