Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 5-1990 The Effects of Methionyl Bovine Somatotropin Administration on Luteinizing Hormone in Dairy Cattle Joseph Charles Dalton Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Dairy Science Commons Recommended Citation Dalton, Joseph Charles, "The Effects of Methionyl Bovine Somatotropin Administration on Luteinizing Hormone in Dairy Cattle" (1990). All Graduate Theses and Dissertations. 4084. https://digitalcommons.usu.edu/etd/4084 This Thesis is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. THE EFFECTS OF METHIONYL BOVINE SOMATOTROPIN ADMINISTRATION ON LUTEINIZING HORMONE IN DAIRY CATTLE by Joseph Charles Dalton A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Dairy Science Approved : UTAH STATE UNIVERSITY Logan, Utah 1990 ii ACKNOWLEDGEMENTS This research project was initiated in February 1989 under the direction of Dr. David P. Marcinkowski. I would like to thank Dave for the many long hours and sleepless nights devoted to this research. Thanks also for providing suggestions, software, and a computer for writing this thesis. Thanks must also be extended to the members of my Graduate Committee: Dr. LeGrande C. Ellis for his guidance and suggestions on the assays and Dr. Donald V. Sisson for his help with the statistical analysis. Others who assisted this research included Dr . Warren C. Foote, who helped analyze the LH data; Dr. Robert C. Lamb, who gave a critical review of the research proposal; Dr. Gary Hartnell and Rick Hoffman of Monsanto Agricultural Company in St. Louis, Missouri, who donated the BST and provided many helpful suggestions; and Raj Juahar, who performed the LH and progesterone assays. I would also like to thank veterinarians Dr . Robert J. Callan, Dr. Jane Kelly, and Drs. Mark and Altina Wickstrom for their help with the catheterizations and weekly palpations. Thanks to Stan Henderson for his cooperation and assistance in locating cows for this study. Thanks also to the many students who restrained animals and collected blood samples. Thanks to my parents, Fred and Irma Dalton, and my iii f amily , Rita and Michael Baumann and Fred and Lisa Dalton, for their love, concern, and support throughout my educational career. Finally, to my wife, Nell, I extend a heartfelt thanks f or the many hours of hard work, sacrifices, suggestions, ·and words of encouragement. I could not have completed this research without her. I will never forget her help. Joseph Charles Dalton i v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS. • . ii LIST OF TABLES .......... .. .. ..... ... ............... ... v LIST OF FIGURES. v i ABSTRACT. • . v i i STATEMENT OF THE PROBLEM .. .. ... .... .. .. .... .. .... .. 1 Introduction. 1 Purpose a nd Objectiv es . .... .. .. ... ... .. ... ... 2 LITERATURE REVIEW. 3 Hy pothalamic-Pituitary Axis .... .... ...... ... ....... 3 The Bovine Estrous Cycle . .. .... .... ... .... ... 4 Bovine Somatotropin (BST) ..... ........ .. ...... .. 5 BST and Milk Producti on ... ............... ... ... .. .. 6 BST, Nutrition and Reproducti on. 8 BST a nd Reproductive Performance ... .... .... 10 MATERIALS AND METHODS. 13 Experimental Design . .... .............. ... ..... .. .. 13 Sta~i ~ tical Analysis ........ ...... ...... .. .... 17 Def~n~t~ons . .. ........... ..... .. • ..... .... .. 17 RES ULTS AND DISCUSSION. 19 Milk Production ...... .... ..... .... ..... ... ... .. 19 LH Concentrations During Prostaglandin Induced Estrus. 21 Basal Collection and GnRH Challe nge .. ...... .. ... 26 CONCLUSIONS . ....... ............. ... ..... ..... 33 RE FERENCES . 3 4 APPENDICES . 41 v LIST OF TAB LES Table Page 1 Experimental design summary .. ..... .... ..... .. 15 2 Summary of the responses to the third prostaglandin injection and subsequent LH peaks captured .. ........ ... .......... ... 22 3 Plasma progesterone profiles and summary of treatment responses ... ... .. ........... ... 44 4 Phase of the estrous cycle at the time of GnRH challenge ................................ 27 5 A treatment group comparison of LH variables during the basal collection period .. ..... .. ...... .. ...... .......... .. 28 6 Paired t-test analysis of LH variables during the basal collection period .......... .. 28 7 A t r eatment group comparison of LH variables during the GnRH challenge period .... ... .. ...... .. ....... .. .. ... ... .. 31 8 Paired t-test analysis of LH variables during the GnRH challenge period ... .... .. .... 31 vi LIST OF FIGURES Figure Page 1 Example of samples used in the calculation of basal values .......... ........ 18 2 The effect of BST on milk production .......... 20 3 LH peak of cow # 6720 (BST) following the third prostaglandin injection .... ........ 23 4 Plasma progesterone profile of cow # 6714 (placebo) showing partial luteolysis following the third prostaglandin injection . .......... ... ...... .. 25 5 Basal LH profile of cow # 6700 (placebo) showing infrequent pulsatile activity ...... .. 53 6 Basal LH profile of cow # 6672 (placebo) showing frequent pulsatile activity ........... 54 7 Mean LH response to the GnRH challenge by treatment group ............................ 30 vii ABSTRACT The Effects of Methionyl Bovine Somatotropin Administration on Luteinizing Hormone in Dairy Cattle by Joseph C. Dalton, Master of Science Utah State University, 1990 Major Professor: Dr. David P. Marcinkowski Department: Animal, Dairy, and Veterinary Sciences sixteen lactating regularly cycling dairy cows (14 primiparous, 2 multiparous) were used to determine the effects of somatotropin administration on basal, peak, and pulse luteinizing hormone concentrations during the breeding period. In addition, the effects of somatotropin administration on the pituitary response to a gonadotropin- releasing hormone challenge was studied. The experimental group received daily somatotropin treatments (25mg) for 24 days. The control group received a daily placebo. All animals were treated with three injections of prostaglandin F2-alpha (25 mgjtreatment) for estrus synchronization. Somatotropin and placebo treatments began with the second prostaglandin injection. Sixty hours following the final prostaglandin injection, all cows were catheterized via a jugular vein. Blood samples were collected at 15-minute intervals for 24 viii hours. The estimated mean time to the preovulatory luteinizing hormone peak was 62.5 +/- 1.8 (SE) hours among 6 of 16 animals responding. Mean plasma peak luteinizing hormone concentration (regardless of treatment) was 13.49 +/- 4 .18 (SE) ngjml. On Day 10 of the subsequent estrous cycle, blood samples were collected at 20-minute intervals for 6 hours to determine basal levels of luteinizing hormone. Immediately fo llowing this collection period, a gonadotropin-releasing hormone challenge (100 ug) was administered intravenously. Blood samples were collected at 15-minute intervals for an additional 8 hours. BST did not affect basal, peak, or pulse luteinizing hormone concentrations . There were no differences in basal luteinizing hormone concentration, pulse amplitude, pulse interval, or pulse frequency. BST did not affect the pituitary response to a gonadotropin-releasing hormone challenge. Time to peak, time to return to basal, peak con­ centration, peak width, and peak luteinizing hormone amplitude were not different among treatment groups following the gonadotropin-releasing hormone challenge. Milk pro­ duction of BST-treated cows was increased 7% (2.1 kg/d) over controls. (65 pages) STATEMENT OF THE PROBLEM Introduction Many dairymen and professionals believe high milk yield and lowered reproductive performance are closely related. Miller et al. (39) observed a direct relationship between the amount of milk produced in the first lactation and a longer calving interval. Stevenson and Britt (57) reported that high levels of milk production and its associated negative energy balance delayed the initiation of postpartum ovarian activity in dairy cattle. Nevertheless, scientists and dairymen continue searching for ways to increase milk production. Semen selection and artificial j nsemination can result in milk production increases of approximately 100 kgjyr (42). Embryo transfer can cause increases of an additional 40 kgjyr (60). Somatotropin (BST) administration has the potential to increase milk production by 2000 kg/lactation (3). Historically, the major focus of BST research has been on the influence of BST on milk production . However, recent research indicates BST may adversely affect reproduction. Hard et al. (31) found days open and calving intervals were higher ( 5 days) in BST-treated cows. In the same study, pregnancy and successful calving rates were 10% lower in EST­ treated cows. Gilts treated with exogenous porcine pituitary somatotropin (PST) showed increased growth rate and improved feed efficiency (9) . However, PST reduced the response of granulosa cells to gonadotropins in vitro and was associated 2 with a delayed onset of puberty (9). In an initial study by Schemm and Deaver (55), BST was shown to have an effect on circulating gonadotropin concentrations in dairy cattle. However, few studies have focused on the effects BST may have on luteinizing