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Experimental assumption of dominance by a smaller follicle and associated hormonal changes in mares.
Abstract: A two-follicle model was used to study the nature of selection of the dominant follicle in mares by ablating neither or one of the two follicles on the day the larger follicle reached >/= 20 mm (Day 0). The larger follicle became the dominant follicle in all mares in which both follicles (n = 8) or only the larger follicle (n = 10) was retained. When only the smaller follicle (n = 9) was retained, it became dominant and ovulated in six mares and became atretic in three mares; the difference in diameter between the two follicles on Day 0 was less (p < 0.01) in mares in which the retained smaller follicle grew and ovulated (2.2 +/- 0.6 mm) than in the mares in which the follicle became atretic (5.9 +/- 1.2 mm). A decline (p < 0. 0001) in FSH concentrations occurred over Days -4 (8.4 +/- 0.7 ng/ml) to 0 (5.9 +/- 0.3 ng/ml), averaged over all groups, and the decline continued for several more days in the groups with both follicles or with only the larger follicle retained. In the group with only the smaller follicle retained, compared to the group with both follicles retained, FSH concentrations and diameter of the smaller follicle increased between Days 0 and 1 (significant interaction for each end point). After Day 1, FSH concentrations continued to increase when the smaller retained follicle became atretic; concentrations decreased when the smaller retained follicle became dominant. An increase (p < 0.0001) in LH concentrations occurred over Days -4 (12.2 +/- 1.1 pg/ml) to 0 (21.1 +/- 2.0 pg/ml), averaged over the three groups. In 23 of 27 mares, a transient peak in LH concentrations occurred within 2 days of Day 0. In the groups with both follicles or with only the larger follicle retained, an increase (p < 0.0001) in systemic estradiol concentrations occurred between Day 0 (5.3 +/- 0.6 pg/ml) and Day 2 (7.5 +/- 0.4 pg/ml). When only the smaller follicle was retained, estradiol did not begin to increase until Day 2, and it increased only when the retained follicle grew and became dominant. The beginning of an increase in estradiol and continued decrease in FSH at the expected beginning of deviation were attributable to the future dominant follicle; there was no indication that the smaller follicle was involved.
Publication Date: 1999-08-24 PubMed ID: 10456850DOI: 10.1095/biolreprod61.3.724Google 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 explored how dominant follicles are selected in mares, discovering that whether a follicle is larger or smaller, it can still become dominant and ovulate under certain conditions, influencing hormone levels.
Methodology
- The researchers used a two-follicle model and performed three different types of interventions: retaining both follicles, retaining only the larger one, and retaining only the smaller one.
- The intervention was performed on the day that the larger follicle reached a size equal to or greater than 20 mm, which the researchers labeled as Day 0.
Results
- In cases where both follicles or only the larger follicle were retained, the larger follicle consistently became the dominant follicle in all the mares.
- When only the smaller follicle was kept, it successfully became dominant and ovulated in six out of the nine mares, while the smaller follicle in the remaining three mares became atretic.
- The researchers also found that the size difference between the two follicles on Day 0 can impact the smaller follicle’s ability to become dominant and ovulate.
- If the size difference was less, the smaller follicle was more likely to develop and ovulate, but if the size difference was more significant, the smaller follicle tended to become atretic.
Hormonal Changes
- The researchers also studied hormonal changes associated with these processes.
- They noted a decline in FSH (Follicle Stimulating Hormone) concentrations from Day -4 to Day 0 in all the groups, with the decline continuing for a few more days in the groups where both or only the larger follicle was retained.
- Conversely, for the group where only the smaller follicle was retained, an increase in FSH concentrations was observed between Day 0 and 1, particularly in situations where the follicle eventually became atretic rather than dominant.
- An increase in LH (Luteinising Hormone) concentrations was also documented over Days -4 to 0 in all groups. In 23 of 27 mares, a peak in LH concentrations was observed within 2 days of Day 0.
- An increase in estradiol concentrations was noticed between Day 0 and Day 2 in the groups where both follicles or only the larger follicle was retained. But when only the smaller follicle was retained, this increase in estradiol began only from Day 2 and continued only if the retained follicle grew and became dominant.
- The researchers attributed the beginning of this increase in estradiol and the continued decline in FSH at the expected beginning of deviation to the future dominant follicle, indicating no involvement from the smaller follicle.
The study hence furthers our understanding of follicle dominance and hormonal changes in mares, which can have implications for breeding management and reproductive health in horses.
Cite This Article
APA
Gastal EL, Gastal MO, Ginther OJ.
(1999).
Experimental assumption of dominance by a smaller follicle and associated hormonal changes in mares.
Biol Reprod, 61(3), 724-730.
https://doi.org/10.1095/biolreprod61.3.724 Publication
Researcher Affiliations
- Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
MeSH Terms
- Animals
- Estradiol / blood
- Female
- Follicle Stimulating Hormone / blood
- Horses / physiology
- Luteinizing Hormone / blood
- Ovarian Follicle / anatomy & histology
- Ovarian Follicle / physiology
- Ovulation
- Time Factors
Citations
This article has been cited 4 times.- Li L, Deng X, Hu S, Cui Z, Ning Z, Gui T, Zhao X, Li D, Wang Y, Yin H, Ye L, Tian Y, Zhang Y, Li H, Zhu Q. Systematic Analysis of Long Noncoding RNA and mRNA in Granulosa Cells during the Hen Ovulatory Cycle. Animals (Basel) 2021 May 25;11(6).
- Ishak GM, Bashir ST, Dutra GA, Gastal GDA, Gastal MO, Cavinder CA, Feugang JM, Gastal EL. In vivo antral follicle wall biopsy: a new research technique to study ovarian function at the cellular and molecular levels. Reprod Biol Endocrinol 2018 Jul 28;16(1):71.
- Ginther OJ, Beg MA, Gastal EL, Gastal MO, Baerwald AR, Pierson RA. Systemic concentrations of hormones during the development of follicular waves in mares and women: a comparative study. Reproduction 2005 Sep;130(3):379-88.
- Medan MS, Nambo Y, Nagamine N, Shinbo H, Watanabe G, Groome N, Taya K. Plasma concentrations of ir-inhibin, inhibin A, inhibin pro-alphaC, FSH, and estradiol-17beta during estrous cycle in mares and their relationship with follicular growth. Endocrine 2004 Oct;25(1):7-14.
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