Changes in the hypothalamic-hypophyseal axis of mares associated with seasonal reproductive recrudescence.
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 changes in the hypothalamus and anterior pituitary during the period of transition from winter anestrus into the breeding season. Mares were of mixed breeding, between the ages of 3 and 20 years, and had shown normal patterns of estrous behavior and ovulation during the breeding season previous to this experiment. Hypothalamic content of gonadotropin-releasing hormone (GnRH) and anterior pituitary content of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were determined by radioimmunoassay. The number of receptors for GnRH in anterior pituitary tissue was also determined. There was no effect of stage of transition into the breeding season on receptors for GnRH or content of FSH (p greater than 0.05). Likewise, content of GnRH in the hypothalamus did not differ between the four groups (p greater than 0.05). However, pituitary content of LH increased progressively from anestrus to the breeding season (p less than 0.05). Means for the AN, ET, LT and EST groups were 1.1 +/- 0.2, 2.2 +/- 0.3, 6.3 +/- 1.4 and 15.2 +/- 1.8 micrograms LH/mg pituitary, respectively. In addition, serum concentrations of LH associated with the first ovulation of the year for 5 of the EST mares were significantly lower (p less than 0.01) than those associated with the second ovulation of the year.(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1986-11-01 PubMed ID: 3028519DOI: 10.1095/biolreprod35.4.897Google 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.
This research investigates the hormonal changes in mares, specifically in the hypothalamus and anterior pituitary gland, during the transition from the inactive breeding season (anestrus) to the active breeding season, focusing on changes in gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
Overview of the Experiment
- The researchers studied four groups of mares which were in different stages of the breeding cycle – anestrus (AN), early transition (ET), late transition (LT), and estrus (EST).
- The mares were aged between 3 to 20 years, of mixed breeding, and had previously shown normal patterns of ovulation and estrous behavior.
- The hormones GnRH, LH, and FSH found in the hypothalamus or anterior pituitary gland were measured using a process known as radioimmunoassay. Additionally, the number of GnRH receptors in the anterior pituitary gland tissue was determined.
Findings of the Research
- The results showed no significant change in the amount of GnRH, FSH, or the number of GnRH receptors across the different groups or stages of transition into the breeding season.
- However, there was a progressive increase in the anterior pituitary content of LH from the anestrus stage to the active breeding season. The mean LH contents for the AN, ET, LT, and EST groups were found to differentiate significantly.
- The researchers also found that the LH concentrations associated with the first ovulation of the year were significantly lower than those associated with the second ovulation amongst the EST group of mares.
Implications of the Findings
- This study contributes valuable insights into mare reproductive biology, aiding in the understanding of hormonal changes associated with the breeding season and ovulation cycle in mares.
- The marked increase in LH content from the anestrus stage to active breeding suggests a crucial role for LH in initiation and maintenance of the mares’ breeding state.
- The variation in LH levels between the first and second ovulation in the year may indicate differences in hormonal regulation during different stages of the breeding season.
Cite This Article
APA
Silvia PJ, Squires EL, Nett TM.
(1986).
Changes in the hypothalamic-hypophyseal axis of mares associated with seasonal reproductive recrudescence.
Biol Reprod, 35(4), 897-905.
https://doi.org/10.1095/biolreprod35.4.897 Publication
Researcher Affiliations
MeSH Terms
- Animals
- Estrus
- Female
- Follicle Stimulating Hormone / analysis
- Gonadotropin-Releasing Hormone / analysis
- Horses / physiology
- Hypothalamo-Hypophyseal System / physiology
- Luteinizing Hormone / analysis
- Periodicity
- Receptors, LHRH / analysis
- Reproduction
- Seasons
Citations
This article has been cited 2 times.- Bianchi CP, Bruno S, Videla Dorna I, Rodríguez E, Aba MA. Effect of short-term artificial light and transvaginal progesterone device on first ovulation in late transitional mares. J Equine Sci 2022 Apr;33(1):1-6.
- Alonso MA, Silva LA, Affonso FJ, Lemes KM, Celeghini ECC, Lançoni R, Carvalho HF, de Arruda RP. Effect of hCG application at different moments of the estrous cycle on corpus luteum and uterine vascularization and serum progesterone concentration in mares. Anim Reprod 2019 Oct 24;16(2):317-327.
Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
