INFLUENCE OF THE LUTEINIZING HORMONE-RELEASING-HORMONE AGONIST, DESLORELIN, ON PATTERNS OF ESTRADIOL-17-BETA AND LUTEINIZING-HORMONE SECRETION, OVARIAN FOLLICULAR RESPONSES TO SUPERSTIMULATION WITH FOLLICLE-STIMULATING-HORMONE, AND RECOVERY AND IN-VITRO DEVELOPMENT OF OOCYTES INHEIFER CALVES

The objective of this study was to determine the effects of inducing p ituitary desensitization by treatment with an LHRH agonist (deslorelin ) on reproductive hormone secretion and ovarian follicular status in h eifer calves, before and during stimulation with FSH. The recovery and in vitro development of oocytes was also investigated. Brahman (Bos i ndices) calves, 6 mo old, received either no treatment from Day 0 to D ay 8 and injections of FSH on Days 9, 10, and 11 (controls, n = 10), o r bioimplants of deslorelin on Day 0 and injections of FSH on Days 9, 10, and 11 (deslorelin calves, n = 10). Ovarian follicular characteris tics were determined on Days -2, 0, and 8 by ultrasonography; follicle sizes (2-4 mm, 5-7 mm, 8-9 mm, or greater than or equal to 10 mm) wer e recorded. Ovaries were removed surgically on Day 12, surface follicl e numbers and sizes were recorded, and oocytes were aspirated, graded (A-grade, B-grade, denuded, atretic), and prepared for in vitro fertil ization and culture. Blood samples were taken throughout the experimen t to monitor plasma concentrations of LH, estradiol-17 beta (estradiol ) and progesterone. Treatment with deslorelin desensitized the pituita ry in heifer calves and altered patterns of LH and estradiol secretion . There were no apparent consistent effects of deslorelin treatment on follicle numbers and growth. A higher number of combined A-grade and B-grade oocytes were obtained from heifers treated with deslorelin, wh ich, in turn, resulted in twice the number of blastocysts. Treatment w ith an LHRH agonist provides a model for studying the hormonal require ments for follicle growth and in vivo oocyte maturation in heifer calv es.