Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2007 Induction of ovulation and LH response in cyclic mares treated with gonadorelin diacetate tetrahydrate Jennifer Ann Ingwerson Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Animal Sciences Commons, Physiology Commons, and the Veterinary Physiology Commons Recommended Citation Ingwerson, Jennifer Ann, "Induction of ovulation and LH response in cyclic mares treated with gonadorelin diacetate tetrahydrate" (2007). Retrospective Theses and Dissertations. 14897. https://lib.dr.iastate.edu/rtd/14897 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Induction of ovulation and LH response in cyclic mares treated with gonadorelin diacetate tetrahydrate by Jennifer Ann Ingwerson A thesis submitted to the graduate faculty in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE Major: Animal Physiology (Reproductive Physiology) Program of Study Committee: Peggy Miller-Auwerda, Co-major Professor Curtis Youngs, Co-major Professor Carolyn Komar Lawrence Evans Iowa State University Ames, Iowa 2007 UMI Number: 1449655 UMI Microform 1449655 Copyright 2008 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, MI 48106-1346 ii Dedication I dedicate this to my dad, James Ingwerson, and my aunt, Linnea Baney, who lead me to horses. I also dedicate this to my mom, Diane Ingwerson, who instilled in me a love of academics. Without them my passion for horses would have never started to lead me down this path in my life. iii TABLE OF CONTENTS LIST OF TABLES.................................................................................................. v LIST OF FIGURES .............................................................................................. vi ABSTRACT..........................................................................................................vii CHAPTER 1. LITERATURE REVIEW ..................................................................1 1.1 Introduction................................................................................................1 1.2 Seasonality................................................................................................2 1.2.1 Estrous cycle.....................................................................................4 1.2.2 Follicular waves.................................................................................4 1.2.3 Hypothalamic-pituitary-gonadal axis .................................................5 1.3 GnRH ........................................................................................................5 1.3.1 GnRH pulsatile release .....................................................................6 1.3.2 Regulation of GnRH ..........................................................................8 1.4 Endocrinology of the estrous cycle ..........................................................10 1.4.1 Follicular phase ...............................................................................10 1.4.2 Luteal phase....................................................................................11 1.5 GnRH analogues/hormones used to control estrus.................................12 1.5.1 Cattle...............................................................................................12 OvSynch…………………………………………………………………13 CO-Synch ……………………………………………………………....13 Select Synch ……………………………………………………………14 1.5.2 Horses………………………………………………..…………………...15 hCG………………………………………………………………………16 iv PGF2α (and analogues)……………………………………………….17 Deslorelin Ovuplant™…………………………………………………18 Deslorelin BioRelease………………………………………………...19 Kisspeptin……………………………………………………………....20 1.5.3 Cystorelin™ (gonadorelin diacetate tetrahydrate) …………………...20 1.6 Rationale for experiment..........................................................................22 1.7 Literature Cited ........................................................................................23 CHAPTER 2. INDUCTION OF OVULATION AND LH RESPONSE IN CYCLIC MARES TREATED WITH CYSTORELIN™…………………………………………28 INTRODUCTION ................................................................................................28 MATERIALS AND METHODS ............................................................................30 Experimental animals ....................................................................................30 Treatments ....................................................................................................30 Blood sample collection.................................................................................31 Assay of plasma LH levels ............................................................................33 Data Analysis.................................................................................................33 RESULTS ...........................................................................................................34 Days to ovulation ...........................................................................................34 LH response ..................................................................................................35 DISCUSSION .....................................................................................................39 LITERATURE CITED..........................................................................................43 ACKNOWLEDGEMENTS ...................................................................................45 v LIST OF TABLES Table 1. Timeline for blood sample collection and treatment with Cystorelin™……………………………………………...…………………………………32 Table 2. Ovarian status and response to treatment with either Cystorelin™ or saline………………………………………………………………………………………..34 vi LIST OF FIGURES Figure 1. Pineal gland control of reproductive seasonality in mares….. ………….....3 Figure 2. Hypothalamic-pituitary-gonadal axis feedback mechanisms in the female……………………………………………………………………………………….10 Figure 3. Methods currently being used to synchronize ovulation in postpartum beef cows: OvSynch, CO—Synch, and Select Synch. …...…………………….…………..15 Figure 4. LH profiles of individual mares treated with Cystorelin™.…………………35 Figure 5. LH profiles of individual mares treated with saline ………….……………..36 Figure 6. Average LH response of treatment and control mares…………………….37 Figure 7. Mean plasma LH increase over time between treatment and control mares…………………………………..........................................……………………...38 vii ABSTRACT Regulating the time of ovulation in the mare has many practical and beneficial management applications, including use with artificial insemination. The objective of the present study was to test the effectiveness of Cystorelin™ (gonadorelin diacetate tetrahydrate) to elicit increased LH secretion and to induce ovulation in cyclic mares. A total of 24 mares of Thoroughbred and stock type breeding was used in this study. Mares possessing an ovarian follicle 3.5 cm to 4.0 cm in diameter were assigned to either treatment with three 75 µg (1.5 mL) i.m. injections of Cystorelin™ or three 1.5 mL i.m. injections of sterile saline (control). Treatment with Cystorelin™ reduced (P < .05) the mean number of days until ovulation (2.25 ± 0.25 vs 3.23 ± 0.41 for Cystorelin™ and saline, respectively), although variation in the time to ovulation was similar (P>.81). Mean plasma LH levels were calculated over four time periods (-30 to 0 (Period 1), 30-120 (Period 2), 150-240 (Period 3), 270-360 min (Period 4)). Luteinizing hormone response was analyzed by comparing the mean LH value of Period 1, 2, and 3 with the baseline mean. Although the level in Period 2 tended (P<.07) to be higher than baseline, LH levels in Periods 3 and 4 were not different from baseline (P>.15, P>.18 respectively). In summary Cystorelin™ effectively hastened ovulation in mares. Further research is necessary to develop a protocol that can also reduce variability in the time of ovulation. 1 CHAPTER 1. LITERATURE REVIEW 1.1 Introduction Regulating the time of ovulation in the mare has many practical and beneficial applications and the increasing use of artificial insemination technologies in the equine industry has increased the importance of controlling the time of ovulation in the mare. Controlling the time of ovulation can increase management and labor efficiency, optimize the time of breeding when using transported semen, and reduce the number of times a mare is bred during a given estrous cycle. In cyclic mares, human chorionic gonadotropin (hCG), prostaglandin F2alpha (PGF2α) (and analogues), and gonadotropin releasing hormone (GnRH) have been used in attempts to control the time of ovulation. A new product to time ovulation in the mare, EquiPure-LH (by AspenBio Pharma) has been sold as a specially labeled reagent to licensed veterinarians since late 2005. AspenBio Pharma is seeking U.S. Food and Drug Administration (FDA) approval. Apparently, no research has been