Selection of the dominant follicle in cattle and horses.
Abstract: The nature of selection of the dominant follicle is reviewed by comparing research results between cattle and horses. In both species, emergence of a follicular wave is stimulated by an FSH surge. The surge reaches a peak by the time the follicles attain 4 mm in diameter in cattle and 13 mm in mares. In cattle, all of the growing follicles >/=5 mm contribute to the decline in FSH concentrations. However, the declining FSH concentrations are still needed by the growing follicles. Several days after the peak of the FSH surge and emergence of the wave, the two largest follicles reach means of 8.5 and 7.7 mm in cattle and 22 and 19 mm in horses. At this approximate time, the follicles begin to undergo deviation in follicle diameters, which is characterized by continued growth of the largest follicle to become the dominant follicle and reduced or terminated growth of the remaining follicles to become subordinate follicles. In both species, on average, the future dominant follicle emerges before the future largest subordinate follicle, and the two follicles grow in parallel until deviation. The difference in diameter between the two largest follicles at the beginning of deviation is equivalent in growth to approximately 8 h in cattle and 24 h in mares. Apparently, this is adequate time for the largest follicle to establish the deviation process before the second-largest follicle reaches a similar diameter. During this time, the largest follicle plays the primary role in further suppressing circulating FSH concentrations to below the requirements of the smaller follicles, which causes their regression. The follicle-produced FSH suppressants appear to be estradiol and inhibin. In addition to enhancing its FSH-suppressing ability, the largest follicle also develops the ability to utilize the reduced concentrations of FSH for its continued growth. It is therefore postulated that the essence of selection of a dominant follicle in these two species is a close two-way functional coupling between changing FSH concentrations and follicle growth and development. Elevated concentrations of circulating LH encompass deviation in both species and may play a role in continued growth of the largest follicle. It is not known if LH begins to be utilized by the largest follicle before, at, or after the beginning of diameter deviation. However, results of studies in mares suggested that LH does not influence growth of the dominant follicle until after the beginning of deviation.
Publication Date: 2000-06-14 PubMed ID: 10844185DOI: 10.1016/s0378-4320(00)00083-xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
- Research Support
- U.S. Gov't
- Non-P.H.S.
- Review
Summary
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The research studies the process of how the dominant follicle is selected in cattle and horses, which is characterized by the emergence of follicular waves stimulated by an FSH surge, contributing to the decline in FSH concentrations, the growth of the largest follicle into the dominant follicle and the reduction of remaining follicles into subordinate ones.
The Role of FSH in Follicular Waves
- An FSH (Follicle-Stimulating Hormone) surge triggers the emergence of a follicular wave in both cattle and horses.
- In cattle, this surge peaks when the follicles reach 4mm in diameter, while in mares, it peaks at 13mm.
- All growing follicles that are more than or equal to 5mm contribute to a decline in FSH concentrations in cattle. However, these declining concentrations are still critical for the growth of the follicles.
Deciding the Dominant and Subordinate Follicles
- Deviation in follicle diameters begins several days after the peak of the FSH surge, marking the selection of the dominant and subordinate follicles.
- The largest follicle continues to grow, becoming the dominant one, while the other follicles end up as lesser, or ‘subordinate’, follicles as their growth is reduced or terminated.
- Interestingly, the future dominant follicle appears before the subordinate follicle does, and they both grow in parallel until deviation.
Establishing Dominance
- What makes the deviation possible is a gap equivalent to approximately 8 hours of growth in cattle and 24 hours in mares between the two largest follicles. This gap provides just enough time for the biggest follicle to establish its dominance before the second largest follicle reaches a similar diameter.
- During this period of deviation, the biggest follicle has a major role in further decreasing FSH concentrations, which causes the smaller follicles to regress.
- Additionally, it produces FSH suppressants, which seem to be estradiol and inhibin, allowing the largest follicle to continue growing, even with reduced FSH levels.
- FSH levels and follicle growth hence demonstrate a tightly coupled two-way functional relationship during the selection of a dominant follicle.
Possible Role of LH
- Increased levels of LH (Luteinizing Hormone) accompany deviation in both species and might play a role in the continued growth of the dominant follicle.
- It’s not clear about when LH begins to be utilized by the largest follicle – this could be before, during, or after the beginning of diameter deviation.
- However, recent studies in mares suggest that LH does not affect the growth of the dominant follicle until after deviation starts.
Cite This Article
APA
Ginther OJ.
(2000).
Selection of the dominant follicle in cattle and horses.
Anim Reprod Sci, 60-61, 61-79.
https://doi.org/10.1016/s0378-4320(00)00083-x Publication
Researcher Affiliations
- Animal Health and Biomedical Sciences, University of Wisconsin-Madison, 53706, USA. ojg@ahabs.wisc.edu
MeSH Terms
- Animals
- Cattle / physiology
- Female
- Follicle Stimulating Hormone / physiology
- Horses / physiology
- Luteinizing Hormone / physiology
- Ovarian Follicle / physiology
- Pulsatile Flow
Citations
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- Marchais M, Gilbert I, Bastien A, Macaulay A, Robert C. Mammalian cumulus-oocyte complex communication: a dialog through long and short distance messaging. J Assist Reprod Genet 2022 May;39(5):1011-1025.
- Cremonesi F, Bonfanti S, Idda A, Lange-Consiglio A. Platelet Rich Plasma for Regenerative Medicine Treatment of Bovine Ovarian Hypofunction. Front Vet Sci 2020;7:517.
- Lu X, Bao H, Cui L, Zhu W, Zhang L, Xu Z, Man X, Chu Y, Fu Q, Zhang H. hUMSC transplantation restores ovarian function in POI rats by inhibiting autophagy of theca-interstitial cells via the AMPK/mTOR signaling pathway. Stem Cell Res Ther 2020 Jul 3;11(1):268.
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