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Follicular waves and circulating concentrations of gonadotrophins, inhibin and oestradiol during the anovulatory season in mares.
Abstract: Follicular waves and associated circulating hormone concentrations were studied during the anovulatory season in pony mares (n=8). Follicles were monitored by ultrasonography and a blood sample was taken daily from 29 January until ovulation (mean, 28 April). A mid-anovulatory period (largest follicle, 16.0+/-0.5 mm in diameter) and transitional period (largest follicle, 22.4+/-0.5 mm) were distinctive in each mare. The two periods were delineated by an increase in the diameter of the largest follicle to >/=21.0 mm. Follicular waves, identified by significant increases in the mean diameter of the second to sixth largest follicles, were detected during both the mid-anovulatory and transitional periods. The mean number of follicles >/=15.0 mm in diameter and the diameter of the second to sixth largest follicles increased in association with statistically identified FSH surges. The pattern of the FSH concentration changes during surges did not change during the mid-anovulatory and transitional periods. During the declining portion of the FSH surge, follicle growth continued and circulating total inhibin increased, indicating suppression of FSH by inhibin from the growing follicles. Circulating oestradiol or LH did not change relative to wave emergence. Results indicated that follicular waves occurred during the second-half of the anovulatory season, even during the period of lowest follicular activity. On a temporal basis, follicular wave emergence was stimulated by surges in circulating FSH. However, the increase in follicle growth to >/=21.0 mm in diameter for the wave at the beginning of the transitional period and for the subsequent waves was not attributable to a change in the characteristics of the associated FSH surges.
Publication Date: 2003-01-18 PubMed ID: 12530925 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
Summary
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This study explores the progression of follicular waves and associated hormone levels during the anovulatory season in pony mares, highlighting that follicular waves can occur even during the season’s period of lowest follicular activity. The research concludes that follicular wave emergence is stimulated by surges in circulating FSH (Follicle Stimulating Hormone).
Study Methodology
- Eight pony mares during their anovulatory season were used for this study.
- The follicles of these mares were examined using ultrasonography daily.
- Blood samples were taken every day from January 29 to the date of ovulation, on average, April 28.
- Two distinct periods were identified, the mid-anovulatory period and the transitional period, marked by an increase in the diameter of the largest follicle to or above 21.0 mm.
- Significant follicular waves were observed during both these periods.
Observations During the Study
- There was an increase in the diameter of the second to sixth follicles during both the mid-anovulatory and transitional periods.
- The mean number of follicles larger or equal to 15.0 mm increased in association with identified FSH surges.
- FSH concentration patterns did not change during these periods.
- Follicle growth continued, and the inhibin hormone levels increased during the declining phase of the FSH surge, representing the inhibitory effect of growing follicles on FSH.
- However, the levels of circulating oestradiol or LH (Luteinizing Hormone) did not have an observable relation with wave emergence.
Findings and Interpretation
- Follicular waves occurred during the second half of the anovulatory season, even during the period of lowest follicular activity.
- It was found that surges in circulating FSH initiated the emergence of follicular waves.
- The surge in follicle growth to 21.0 mm or more in diameter during the beginning of the transitional period and for the subsequent waves was observed to be independent of any changes in the attributes of the affiliated FSH surges.
Cite This Article
APA
Donadeu FX, Ginther OJ.
(2003).
Follicular waves and circulating concentrations of gonadotrophins, inhibin and oestradiol during the anovulatory season in mares.
Reproduction, 124(6), 875-885.
Publication
Researcher Affiliations
- Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, WI 53706, USA.
MeSH Terms
- Anestrus / metabolism
- Animals
- Estradiol / blood
- Female
- Follicle Stimulating Hormone / blood
- Gonadotropins, Pituitary / blood
- Horses / metabolism
- Inhibins / blood
- Luteinizing Hormone / blood
- Ovarian Follicle / metabolism
Citations
This article has been cited 4 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.
- Venegas-Meneses B, Padilla JF, Juárez CE, Morán JL, Morán C, Rosas-Murrieta NH, Handal A, Domínguez R. Effects of ovarian dopaminergic receptors on ovulation. Endocrine 2015 Dec;50(3):783-96.
- Birtch RL, Baerwald AR, Olatunbosun OA, Pierson RA. Ultrasound image attributes of human ovarian dominant follicles during natural and oral contraceptive cycles. Reprod Biol Endocrinol 2005 Apr 13;3:12.
- Khan IU, Khairullah AR, Khan AY, Rehman AU, Mustofa I. Strategic approaches to improve equine breeding and stud farm outcomes. Vet World 2025 Feb;18(2):311-328.
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