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Home / Equine Research Bank / Anim Reprod Sci / Reproductive cycles of horses.
Animal reproduction science2011; 124(3-4); 220-228; doi: 10.1016/j.anireprosci.2011.02.005

Reproductive cycles of horses.

Abstract: Horses are long-day breeders. During the breeding season, cycle length is about 22 days with 5-7 days of oestrus. Gonadotroph cells are localized in the pars distalis as well the pars tuberalis of the pituitary and heterogeneity in the pattern of LH and FSH storage within the gonadotroph population is considered the basis for the differential regulation of gonadotrophin secretion throughout the reproductive cycle. No short and distinct periovulatory LH peak exists in the mare. The equine ovary has an extreme large size and weight. One to two major follicular waves develop per cycle. The preovulatory follicle reaches an average size of 40 mm. Only granulosa cells develop into luteal cells. Progesterone increases at the time of ovulation and reaches maximal concentrations on day 8. Functional luteolysis occurs around day 15 and is initiated by endometrial secretion of PGF(2α). In contrast to other species, no significant luteal oxytocin synthesis exists in the mare. During the oestrous cycle, uterus, vagina and endometrium undergo pronounced changes related to variations in the endocrine milieu. Seasonal reproductive activity is stimulated by photoperiod together with exogenous factors. The anovulatory season can be differentiated into an autumn transitional phase, a mid-anovulatory period and a spring transitional phase bringing the mare back into cyclic activity. During the mid-anovulatory period, follicular development is minimal. The beginning of the spring transitional period is characterized by the development of 1-3 anovulatory follicular waves before ovulation occurs and the most important factor for the re-initiation of ovulatory activity is the occurrence of repeated pronounced increases in circulating LH.
Copyright © 2011 Elsevier B.V. All rights reserved.
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Publication Date: 2011-02-18 PubMed ID: 21377299DOI: 10.1016/j.anireprosci.2011.02.005Google Scholar: Lookup
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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 research article examines the reproductive cycles of horses, exploring the specifics of the process including the influence of the seasons and the roles of various hormones such as LH and FSH in regulating reproduction.

Understanding the Reproductive Cycle

  • The article presents characteristics of horses as being long-day breeders with an average cycle length of about 22 days during the breeding season, which includes 5-7 days of oestrus (the period of sexual receptivity).
  • The research highlights the crucial role of Gonadotroph cells in regulating the secretion of reproductive hormones LH and FSH. These cells are found in the pars distalis and the pars tuberalis regions of the pituitary gland.
  • A unique characteristic of horses is the absence of a short and pronounced LH peak during ovulation, which is commonly found in other species.

The Equine Ovary and Endocrine Changes

  • The researchers point out that equine ovaries are extraordinarily large. During a cycle, one to two major follicular waves develop and the preovulatory follicle grows to an average size of 40 millimeters.
  • There is a transformation of only granulosa cells into luteal cells. Associated with this process, Progesterone levels increase at the time of ovulation, peaking on day 8 before subsiding around day 15 due to functional luteolysis initiated by the secretion of PGF(2α) from the endometrium.
  • Notably, unlike other species, horses do not demonstrate significant synthesis of luteal oxytocin.
  • Significant changes occur in the uterus, vagina, and endometrium during the oestrous cycle due to variations in endocrine hormones.

Seasonal Impact on Reproduction

  • The activation of horses’ seasonal reproductive activity is regulated by photoperiod and other exogenous factors.
  • The research splits the anovulatory season (when the mare does not ovulate) into three phases: an autumn transitional phase, a mid-anovulatory period, and a spring transitional phase.
  • The mid-anovulatory period is marked by minimal follicular development while the spring transitional phase initiates with the development of 1-3 anovulatory follicular waves prior to ovulation.
  • The re-initiation of ovulatory activity is set into motion by the occurrence of repeated increases in circulating LH, a key reproductive hormone.

Cite This Article

APA
Aurich C. (2011). Reproductive cycles of horses. Anim Reprod Sci, 124(3-4), 220-228. https://doi.org/10.1016/j.anireprosci.2011.02.005

Publication

Animal reproduction science
ISSN: 1873-2232
NlmUniqueID: 7807205
Country: Netherlands
Language: English
Volume: 124
Issue: 3-4
Pages: 220-228

Researcher Affiliations

Aurich, Christine
  • Centre for Artificial Insemination and Embryo Transfer, University of Veterinary Sciences, Veterinärplatz 1, Vienna, Austria. christine.aurich@vu-wien.ac.at

MeSH Terms

  • Animals
  • Estrous Cycle / physiology
  • Female
  • Horses / physiology
  • Male
  • Ovarian Follicle / physiology
  • Pregnancy
  • Reproduction / physiology
  • Seasons

Citations

This article has been cited 28 times.
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