Deslorelin) Implant During and After the Postpartum Summer Heat-Stress Period in Dairy Cattle
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REPRODUCTIVE, OVARIAN AND UTERINE RESPONSES TO A GNRH-AGONIST (DESLORELIN) IMPLANT DURING AND AFTER THE POSTPARTUM SUMMER HEAT-STRESS PERIOD IN DAIRY CATTLE By FLÁVIO TEIXEIRA SILVESTRE A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003 Copyright 2003 by Flávio Teixeira Silvestre Dedicated to Juliana, Pai and Mãe, Gustavo, Paula and Daniel ACKNOWLEDGMENTS I would like to express my appreciation to Dr. William W. Thatcher for the opportunity to join this graduate program and financial support. Doctor Thatcher’s enthusiasm, knowledge and hard work have been an example for me and influenced me as a person and professional. I extend my appreciation to Dr. Peter J. Hansen and Dr. Louis F. Archbald, members of my committee, for their valuable suggestions on my experiments during formal and informal discussions. I would like to thank friends and colleagues in our laboratory who have been supportive and always helpful during my entire program: Dr. Metin Pancarci, Dr. Shun Kamimura, Dr. Aydin Guzeloglu, Todd Bilby, Alvaro Arteche, Ricardo Mattos and Oscar Hernandez. Special thank go to Marie Joel Thatcher for her endless help on computer programming and hormone assays. I would like to acknowledge friends in the Animal Science Department: Jeremy Block, Marcio Libone, Maria Padua, Mirian Lopes. I extend my appreciation to all friends in Gainesville who made Juliana and myself feel closer to home: Eduardo Carlos and family, Steel Vasconcelos and family, Marcelo and Aline Carvalho, Luis Lima and family, Whocely Vitor and family. I extend my appreciation to Shirley who was my family during the period prior to this program. iv I would like to express my appreciation to Peter Gelber and staff at Alliance Dairies for the expert management of experimental cows. v TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................................................................................. iv LIST OF TABLES............................................................................................................. ix LIST OF FIGURES ........................................................................................................... xi ABSTRACT..................................................................................................................... xiii CHAPTER 1 INTRODUCTION ........................................................................................................1 2 LITERATURE REVIEW .............................................................................................5 Introduction...................................................................................................................5 Effects of Heat Stress on Reproduction........................................................................6 Effects on estrus behavior .....................................................................................6 Effects on fertility..................................................................................................6 Effects on follicular dynamics...............................................................................7 Effects on Corpus Luteum...................................................................................10 Effects on oocyte .................................................................................................11 Heat-Stress Carry Over Effects ..................................................................................14 Increasing Autumn Fertility........................................................................................16 Embryological Origin of the Pituitary Gland .............................................................18 Pituitary Histology and Anatomy ...............................................................................19 Gonadotropin-Releasing Hormone Receptor .............................................................20 Regulation of GnRHr..................................................................................................22 GnRH Molecule..........................................................................................................23 GnRH-Agonist Deslorelin ..........................................................................................24 GnRH-Agonist Treatments.........................................................................................25 Initiation of Follicle Growth.......................................................................................26 Follicular Recruitment and Dominance......................................................................32 Follicular Dynamics Using a GnRH-Agonist.............................................................35 GnRH-Agonist Recovery............................................................................................36 Follicular Dynamics During GnRH-Agonist Treatment. ...........................................38 Possible Mechanisms of GnRH-Agonist Treatment on Milk Yield...........................39 Role of Growth Hormone in lactation.................................................................40 Growth Hormone responses to GnRH-Agonists .................................................41 Prolactin responses to GnRH-Agonists...............................................................42 vi Estradiol responses ..............................................................................................44 Influences of Uterus – Ovarian Interactions and GnRH-Agonist in Postpartum Uterine Involution in Cattle ...................................................................................45 Uterine Physical Involution ........................................................................................46 Uterine Histological Involution ..................................................................................47 Uterine Mechanisms of Involution .............................................................................48 Uterine Infections .......................................................................................................49 Evaluation of Uterine Involution................................................................................52 Postpartum Ovulation .................................................................................................53 Role of Progesterone...................................................................................................56 Role of Estradiol.........................................................................................................59 Role of Prostaglandin .................................................................................................62 Role of Oxytocin.........................................................................................................65 Delaying First Ovulation Postpartum .........................................................................67 Direct Effects of Gonadotrophins on the Reproductive Tract...................................68 Uterine Histology Upon Chronic GnRH-Agonists.....................................................70 3 REPRODUCTIVE RESPONSES FOLLOWING SUPPRESSION OF FOLLICULAR DEVELOPMENT WITH A DESLORELIN IMPLANT DURING SUMMER HEAT STRESS........................................................................72 Introduction.................................................................................................................72 Materials and Methods ...............................................................................................74 Implant removal...................................................................................................75 Ultrasound (ovarian activity)...............................................................................76 Ultrasound (ovarian recovery).............................................................................77 Synchronization protocol.....................................................................................78 Ultrasound (pregnancy diagnosis).......................................................................80 Resynchronization protocol.................................................................................80 Body condition score (BCS)................................................................................81 Blood samples and hormone assays ....................................................................81 Milk yield ............................................................................................................83 Temperature Humidity Index (THI)....................................................................83 Statistical Analysis......................................................................................................84 Results.........................................................................................................................85 Temperature Humidity Index ..............................................................................85 Day 7 postpartum P4 ............................................................................................86 Ovarian responses................................................................................................86 Frequencies of Cyclic and Ovulation Status for All Cows..................................92 First service reproductive responses....................................................................95