The influence of age, antral follicle count and diestrous ovulations on estrous cycle characteristics of mares

Claes, A.; Ball, Barry A.; Scoggin, Kirsten E.; Roser, Janet F.; Woodward, Elizabeth M.; Davolli, Gabriel Monteiro; Squires, E.L.; Troedsson, Mats H.T.

doi:10.1016/j.theriogenology.2017.04.019

Cited by 21 publications

(23 citation statements)

References 32 publications

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“…There is broad agreement that aging changes not only ovarian function but the reproductive axis in general (Brann & Mahesh 2005, Prior 2005, Carnevale 2008, Kermath & Gore 2012, Claes et al 2017, and this might also have been a significant factor in this study. Consistent with involvement of the hypothalamic-pituitary axis in reproductive aging, the rate of double ovulations increases as mares age (Davies Morel & O'Sullivan 2001).…”

Section: Discussionsupporting

confidence: 57%

Anti-Müllerian hormone and ovarian aging in mares

Uliani

Conley

Corbin

et al. 2019

Journal of Endocrinology

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Anti-Müllerian hormone (AMH) is used as a marker of follicle population numbers and potential fertility in several species including horses but limited data exist across the lifespan. No one has decreased ovarian reserve experimentally to investigate whether a corresponding, quantitative decrease in AMH results. Concentrations of AMH across the lifespan were compiled from 1101 equine females sampled from birth to >33 years of age. Young and old mares (averaging 6 and 19 years) were hemi-ovariectomized and circulating AMH was assessed before and daily thereafter for 15 days. The remaining ovary was removed later and blood was drawn again before and after this second surgery for AMH determination. Polynomial regression analysis and analysis of mares grouped by 5-year intervals of age demonstrated AMH concentrations to be higher in mares aged 5–10 and 10–15 years than 0–5 years of age and lower in mares after 20 years of age. There was high variability in AMH concentrations among neonatal fillies, some of which had concentrations typical of males. Hemi-ovariectomy was followed by a decrease of AMH, almost exactly halving concentrations in intact mares. Concentrations of AMH had returned to intact levels in old mares before complete ovariectomy, as if exhibiting ovarian compensatory hypertrophy, but recovery of AMH was not evident in young mares. AMH may reflect ovarian senescence in mares after 20 years of age but is too variable to do so in the first two decades of life. The ovarian endocrine response to hemi-ovariectomy in mares appears to change with age.

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Section: Discussionsupporting

confidence: 57%

Anti-Müllerian hormone and ovarian aging in mares

Uliani

Conley

Corbin

et al. 2019

Journal of Endocrinology

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“…1,2 The size of the pool of non-growing follicles (NGF), which includes primordial, intermediate and small primary follicles, varies greatly between individuals and species and is also age-dependent. [2][3][4][5][6][7][8][9] The total number of resting follicles at birth averages 520'000 in humans and 150'000 in bovines. 3,8 Estimates for the number of oocytes present in the ovaries of the mare at birth are not available.…”

Section: Introductionmentioning

confidence: 99%

“…3,4,8 The ovarian reserve is defined as the number of follicles left in the ovaries at a given time and can only be accurately assessed post mortem since follicles cannot be measured by clinical methods before having reached the antral stage. [9][10][11][12] Antral follicles are fluid-filled with a diameter ≥ 2 mm and can therefore be visualized by transvaginal (women, cows) or transrectal (cows, mares) ultrasonography. [13][14][15][16][17][18] Their number is directly related to the number of primordial follicles, and the antral follicle count (AFC) is highly repeatable within individuals and widely used as quantitative marker of the ovarian reserve.…”

Section: Introductionmentioning

confidence: 99%

Relationships between antral follicle count, blood serum concentration of anti-Müllerian hormone and fertility in mares

Traversari

Aepli

Knutti³

et al. 2019

SAT

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The anti-Müllerian hormone (AMH) plays an inhibitory role during folliculogenesis by regulating the number of follicles entering the growing pool. Antral follicle counts (AFC) are highly correlated with serum AMH concentrations and both appear to be related to the ovarian reserve in several species. Few data on AMH and AFC in mares exist, especially with regard to fertility. Therefore, the objective of the current study was to investigate the interrelationship between antral follicle count, serum AMH concentrations and fertility outcome in mares. One hundred and twenty-seven mares were enrolled in the study and grouped according to their reproductive status. Around time of estrus, serum AMH concentrations and AFC before and after ovulation were determined. Mares were artificially inseminated and pregnancy diagnosis was performed 14 to 18 days later. A high inter-individual variability in AFC and AMH concentration and a positive relationship between AMH and AFC for follicles 30 mm in diameter were observed, with a stronger correlation in mares older than 18 years. A high correlation between AFC measurements before and after ovulation was identified. The AFC after ovulation was higher than AFC before ovulation. AMH concentrations were neither related to the mares' reproductive status nor to age, number of cycles needed for pregnancy and pregnancy outcome. Excepted for a higher AFC in the middle-aged mares (9-18 years) compared to the younger mares (< 9 years), no associations between AFC and age, reproductive status as well as fertility of mares were found. This study confirms the relationship between AFC and AMH and a high degree of reproducibility of AFC measurements. However, based on our findings, neither AFC nor AMH are useful predictors of fertility in mares.

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“…Those with an interval of 26 days were at the very extreme of that considered normal for mixed breed light horses [19] though these mares were normal by all clinical measures. Observations were insufficient to determine if cycle length in these mares was associated with diestrous ovulations [20]. This seems unlikely in view of the fact that there were no inter-ovulatory increases in inhibin-A or inhibin-B concentrations detected in those mares, but may well have been the case for the other 2 mares with 40 and 45 day inter-ovulatory intervals.…”

Section: Discussionmentioning

confidence: 87%

Inhibin-A and inhibin-B in cyclic and pregnant mares, and mares with granulosa-theca cell tumors: Physiological and diagnostic implications

et al. 2018

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Studies in mares have examined serum inhibin concentrations using immuno-assays unable to distinguish dimeric inhibin-A from inhibin-B isoforms. Inhibin-A and inhibin-B immuno-assays were used to investigate concentrations in cyclic mares, young and old (6 vs 19 years old, respectively) mares following hemi-ovariectomy, mares during pregnancy and in mares with confirmed granulosa cell tumors (GCTs). Mares with inter-ovulatory intervals of 26 days had ovulatory peaks of inhibin-A averaging 80 pg/mL with a mid-cycle nadir of 5 pg/mL. Inhibin-A and inhibin-B concentrations were highly correlated (r = + 0.79, P < 0.01) though peak and nadir concentrations of inhibin-B were not significantly different. However, the ratio of inhibin-A to inhibin-B (A/B) changed significantly through the cycle, highest at ovulation and <1 (more inhibin-B than -A) at mid-cycle. Two mares with grossly extended inter-ovulatory intervals demonstrated mid-cycle inhibin-A (and inhibin-B) excursions suggestive of follicular waves. Follicle-stimulating hormone was negatively correlated with inhibin-A and -B concentrations in all 6 mares. Hemi-ovariectomy in young mares resulted in a significant decrease in inhibin-A and inhibin-B concentrations one day later (P < 0.05) but older mares did not, suggesting a possible extra-ovarian source(s) of these hormones. Both inhibin isoforms dropped to very low levels during pregnancy (P < 0.0001), inhibin-A (P < 0.0001) more rapidly than -B (P < 0.05), so that inhibin-B became the predominant measured form throughout most of gestation (P < 0.05). Mares with confirmed GCTs had elevated inhibin-B concentrations more reliably than inhibin-A but neither inhibin-A or -B was correlated with anti-Müllerian hormone concentrations. Collectively, concentrations of inhibin-A and -B were aligned with physiological events in healthy mares, though more pronounced cyclic changes were seen with inhibin-A. Inhibin-B concentrations were significantly associated with GCTs (P < 0.01), inhibin-A concentrations were not. While both inhibin-A and -B concentrations track physiological events such as cyclic follicular activity, only inhibin-B concentrations effectively signal ovarian neoplasia in mares.

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The influence of age, antral follicle count and diestrous ovulations on estrous cycle characteristics of mares

Cited by 21 publications

References 32 publications

Anti-Müllerian hormone and ovarian aging in mares

Anti-Müllerian hormone and ovarian aging in mares

Relationships between antral follicle count, blood serum concentration of anti-Müllerian hormone and fertility in mares

Inhibin-A and inhibin-B in cyclic and pregnant mares, and mares with granulosa-theca cell tumors: Physiological and diagnostic implications

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