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Pituitary responsiveness of mares challenged with GnRH at various stages of the transition into the breeding season.
Abstract: Four groups of mares, representing anestrus (AN; n = 8), early transition (ET; n = 7), late transition (LT; n = 8) and estrus (EST; n = 12) were used to examine release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) after a bolus injection of gonadotropin releasing hormone (GnRH) during the transition from anestrus into the breeding season. Estrous mares received GnRH on d 2 or 3 of estrus in the cycle immediately preceding slaughter. Anestrous, ET and LT mares received GnRH exactly 1 wk prior to slaughter. A single injection of GnRH (Sigma LHRH, L-0507, 2.0 micrograms/kg body weight in .9% saline, iv) was given to each mare. Blood samples were collected at -2, h, -1 h, directly prior to GnRH, then 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 300, 360, 420 and 480 min post-injection. Maximum release of LH and FSH was observed within 30 min after injection of GnRH. Except for the LH response in EST mares, concentrations of both hormones had returned to pre-injection baseline levels within 8 h. Group means for area under the curve (AUC) of concentrations of LH in serum, and the maximum amount (MAX) of LH quantified in serum, post-GnRH, increased (P less than .05) progressively from AN to the breeding season. The AUC and MAX responses for FSH showed a reverse pattern, decreasing (P less than .05) from AN to the breeding season.(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1987-03-01 PubMed ID: 3106292DOI: 10.2527/jas1987.643790xGoogle Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
The study investigates the release pattern of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in mares following an injection of gonadotropin releasing hormone (GnRH) during different stages of reproductive transition. The research revealed alterations in the release of these hormones based on the reproductive stage with LH concentration changes from anestrus to the breeding season.
Research Methodology
- The study divided mares into four groups based on their reproductive stages: anestrus (AN), early transition (ET), late transition (LT) and estrus (EST).
- Each mare in the group was given a bolus injection of GnRH. The estrous group mares received the hormone on day 2 or 3 of estrus in the cycle just before slaughter. In contrast, the other groups’ mares received their injections one week before slaughter.
- They collected blood samples at several intervals before and after the injection to analyze the concentration of LH and FSH.
Research Findings
- The results showed that the maximum release of both LH and FSH occurred within 30 minutes after the injection of GnRH.
- The exception was observed in the estrous phase group, where LH concentration did not return to pre-injection levels within 8 hours.
- In terms of LH, the area under the curve (AUC) of concentrations and maximum quantities found in serum post-GnRH increased progressively from the anestrus phase to the breeding season – suggesting the role of GnRH increases in mares throughout the stages of reproductive transition.
- Conversely, these measurements showed a decreasing pattern for FSH quantity from anestrus to the breeding season – indicating that the influence of GnRH on FSH decreases as the mare moves closer to the breeding phase.
Study Conclusion
- The patterns of LH and FSH release in response to GnRH vary with the stage of reproductive transition, with significantly differing hormonal dynamics during anestrus, early transition, late transition, and the estrus.
Cite This Article
APA
Silvia PJ, Squires EL, Nett TM.
(1987).
Pituitary responsiveness of mares challenged with GnRH at various stages of the transition into the breeding season.
J Anim Sci, 64(3), 790-796.
https://doi.org/10.2527/jas1987.643790x Publication
Researcher Affiliations
MeSH Terms
- Anestrus / drug effects
- Animals
- Estrus / drug effects
- Female
- Follicle Stimulating Hormone / metabolism
- Horses / physiology
- Luteinizing Hormone / metabolism
- Pituitary Hormone-Releasing Hormones / pharmacology
Citations
This article has been cited 1 times.- Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K. Effect of birth month on endocrine function in Thoroughbred foals born in Hokkaido, the northern part of Japan. J Vet Med Sci 2025 Jul 7;87(7):804-815.
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