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Title:The effectiveness and efficiency of ovulation induction agents in mares
Author(s):Sauberli, Debra
Advisor(s):Herrmann, John A.
Department / Program:Vet Clinical Medicine
Discipline:VMS-Veterinary Clinical Medcne
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):ovulation induction
human chorionic gonadotropin (hCG)
interovulatory period
Abstract:Study 1: A retrospective analysis of the effects of hCG and deslorelin on the reproductive efficiency on two commercial horse farms. Reproductive data from two central Illinois horse farms was analyzed to compare the effectiveness of hCG (Chlorulon™) and a sustained release implant formulation of deslorelin (Ovuplant™) for inducing ovulation and their overall effect on reproductive efficiency. Data were collected over 3 consecutive years, from 1999-2001; a total of 1422 cycles were examined from 658 mares. Of the 1422 cycles examined, 383 were treated with hCG, 451 with deslorelin and 583 cycles were untreated. Mares in this study were over 2.1 times more likely to become pregnant if ovulation was induced (p<.001). Mean days to ovulation was significantly shortened by using hCG or deslorelin compared to no treatment for all follicle sizes except those >45 mm (p=.001). Time from treatment to ovulation was affected by follicle size at time of treatment and by treatment given. When treatment was given at follicle sizes from 35 mm-39 mm, time to ovulation was shorter with deslorelin (2.02 days) than with hCG (2.68days) (p=.000). The number of palpations was not decreased by the use of ovulation induction but follicle size at administration and day of administration showed a positive effect on reducing the number of palpations. Administration of either agent at the first breeding examination when follicles were less than 35 mm in diameter decreased the number of palpations per cycle by one in comparison to non-treated mares. (p=.009) Fewer artificial inseminations per cycle were performed using deslorelin for follicles between 35 and 44 mm compared no treatment [35-39 mm follicles (p=.000): deslorelin 1.21 AI, untreated 1.39 AI; 40-44 mm follicles(p=.000): deslorelin 1.16 AI, untreated 1.48 AI] . Administration of either hCG or deslorelin to mares possessing a <35 mm follicle at the first breeding exam decreased the number of artificial inseminations required per cycle by 1 (p=.001). Both agents performed equally well at inducing ovulation within 48 hours of administration. Deslorelin appeared more consistent in decreasing the days to ovulation in comparison to hCG . Deslorelin decreased the days to ovulation at <35 mm follicles (p=.001)[deslorelin, 2.34 days, hCG 2.57days, untreated 3.54days], 35-39 mm follicles (p=.000) [deslorelin 2.02 days, hCG 2.68 days, untreated 3.87 days] and 40-44mm follicles (p=.000) [deslorelin 2.10 days, hCG 2.47 days, untreated 3.49 days] , Human chorionic gonadotropin only decreased the days significantly on follicles sized between 35-39 and 40-44 mm. Deslorelin also significantly decreased the days to ovulation over hCG at follicles sized between 35-39 mm. Use of these agents in a commercial breeding setting appears to be of value for improving pregnancy rate and decreasing the time to ovulation for improved timing of insemination. Management of the estrus cycle of the mare will determine if ovulation induction decreases the number of palpations and artificial inseminations per cycle. Management schemes must be considered in evaluating effectiveness of ovulation induction drugs since time of administration within the cycle and size of follicle at administration appear to affect reproductive efficiency. Study 2: Effect of deslorelin sustained release implants on the interovulatory period and response to PGF2 administration 6 days after ovulation Ovuplant™ is a sustained release implant that contains the gonadotropin releasing hormone (GnRH) agonist deslorelin. Subcutaneous administration to a mare during estrus will induce ovulation within 48 hours. Clinical evidence suggests that Ovuplant™ causes an increase in the interovulatory period of mares not conceiving on the treated cycle. A down regulation of the hypothalamic pituitary axis is thought to be the main cause of the increased interovulatory interval but no investigation has occurred concerning the function of the corpus luteum formed by ovulation induction by Ovuplant™. This study was performed using six teaching mares at the University of Illinois Veterinary Teaching Hospital in a cross over design clinical trial with four treatment cycles: a control (untreated cycle), a natural cycle with luteolysis induced with prostaglandin F2 alpha (PGF2α), a cycle with ovulation induced with Ovuplant™, and a final cycle with ovulation induced with Ovuplant™ and luteolysis induced with prostaglandinF2alpha (PGF2α). Progesterone levels for assessment of corpus luteum function were determined every three days during the diestrus period and days between ovulations on each treatment cycle determined the interovulatory period. The goals of the study were to determine the effect of Ovuplant™ administration on the interovulatory period, to examine the progesterone production of the corpus luteum formed after ovulation induction with Ovuplant™, and to determine the response of the corpus luteum formed by Ovuplant™ to induced luteolysis. Progesterone levels differed between control mares and mares induced to ovulate with Ovuplant and administered prostaglandin 6 days after corpus luteum formation (p=.02). The interovulatory periods of mares treated with Ovuplant™ (26.00d) did not differ significantly from untreated mares(21.67 days) (p=..01). The interovulatory periods of untreated mares administered prostaglandin (11.8 days) differed significantly from those treated with Ovuplant™ (26.00days) (p=.01). Four mares treated with Ovuplant™ experienced delayed returns to estrus of 3-25 days. Ovuplant™ did not induce a corpus luteum which differed in progesterone production or its ability to respond to PGF2α. Ovuplant™ appears to extend the interovulatory period of sensitive mares.
Issue Date:2014-01-16
Rights Information:Copyright 2013 Debra Sauberli
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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