Effect of constant administration of a gonadotropin-releasing hormone agonist on reproductive activity in mares: induction of ovulation during seasonal anestrus.
Abstract: The potential of a gonadotropin-releasing hormone (GnRH) agonist (goserelin acetate), delivered constantly for 28 days via a subcutaneous depot, to induce ovulation in seasonally anestrous mares, was investigated. Two experiments were conducted, in which a range of doses (30 to 240 micrograms/mare/d) was examined. Mares were selected on the basis of lack of substantial follicular development (follicle diameter < 20 mm determined ultrasonically) and low serum concentrations of luteinizing hormone (LH) and progesterone. Constant administration of the GnRH agonist-induced ovulation in anestrous mares, but a dose-response relation was not observed. Furthermore, with identical doses tested in consecutive or alternate years, considerable variation was observed in the ovulatory response. In general, ovulation in all treated mares was accompanied by increased circulating concentrations of LH and a decrease in follicle-stimulating hormone values. Ovulation was preceded by an increase in estradiol and LH concentrations. In mares in which ovulation did not occur, concentration of LH increased during agonist treatment, whereas that of follicle-stimulating hormone either increased or did not change. It was concluded that constant administration of GnRH agonists may induce ovulation in mares during seasonal anestrus; however, percentage of mares ovulating and the lack of reproducibility of effect indicate that this approach is inappropriate for use as a reliable method to manipulate breeding activity in commercial broodmares.
Publication Date: 1993-10-01 PubMed ID: 8250401
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- Clinical Trial
- Journal Article
- Randomized Controlled Trial
- Research Support
- Non-U.S. Gov't
Summary
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This research investigates whether a hormone treatment can stimulate ovulation in horses outside their normal breeding season. However, the inconsistency of results suggest this is not a reliable option for breeding management in commercial settings.
Objective of Research
- The main aim of this study was to explore the effect of a gonadotropin-releasing hormone (GnRH) agonist on mares during their seasonally anestrous period. This hormone was delivered via a subcutaneous depot for 28 days to see whether it could trigger ovulation.
Design and Methodology
- Two experiments were conducted using various doses of the GnRH agonist, ranging from 30 to 240 micrograms.
- The mares involved in the study were selected because they showed no significant follicular development and had low serum concentrations of luteinizing hormone (LH) and progesterone.
Results and Observations
- It was observed that the constant administration of the GnRH agonist could induce ovulation in anestrous mares, but a dose-response relation was not observed.
- Despite using identical doses, considerable variation was seen in the ovulatory response when tested in consecutive or alternate years.
- All mares that underwent ovulation displayed increased circulating concentrations of LH and a decrease in follicle-stimulating hormone values.
- Before ovulation occurred, it was preceded by an increase in estradiol and LH concentrations.
- In mares where ovulation did not occur, the concentration of LH increased during agonist treatment, whereas follicle-stimulating hormone levels either increased or showed no change.
Conclusion and Implication
- The study concluded that while constant administration of GnRH agonists could induce ovulation in mares during seasonal anestrus, the lack of consistent results indicated that this could not be a reliable method for breeding management.
- This inconsistency makes it unsuitable for application in commercial broodmares where reliable ovulation and conception rates are crucial.
Cite This Article
APA
Fitzgerald BP, Meyer SL, Affleck KJ, Silvia PJ.
(1993).
Effect of constant administration of a gonadotropin-releasing hormone agonist on reproductive activity in mares: induction of ovulation during seasonal anestrus.
Am J Vet Res, 54(10), 1735-1745.
Publication
Researcher Affiliations
- Department of Veterinary Science, Maxwell Gluck Equine Research Center, University of Kentucky, Lexington 40546-0099.
MeSH Terms
- Anestrus / drug effects
- Animals
- Estradiol / blood
- Female
- Gonadotropins, Pituitary / blood
- Goserelin / pharmacology
- Horses / blood
- Horses / physiology
- Ovulation Induction / methods
- Ovulation Induction / veterinary
- Progesterone / blood
Citations
This article has been cited 1 times.- Tsukada T, Kojima AY, Sato K, Moriyoshi M, Koyago M, Sawamukai Y. Intrafollicular Concentrations of Steroid Hormones and PGF2α in Relation to Follicular Development in the Mares during the Breeding Season. J Equine Sci 2008;19(2):31-4.
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