Anti-Müllerian hormone and ovarian aging in mares

Abstract

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.

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

“…Furthermore, others reported that AMH concentrations begin to decline in mares only after 20 years of age. 43 In contrast, in our study older mares didn't have significantly lower AMH and AFC measurements compared to other age groups, but the AFC was higher in mid-dle-aged mares than in young mares. This could be explained by the relatively unequal distribution of mares between the different age groups in our study, but also by the previously reported large individual differences in follicular populations between individuals of the same age.…”

“…Associations between these two biomarkers and age have been demonstrated in mares, cows and women, and are likely to reflect the follicular origin of AMH and the diminishing ovarian reserve. 8,15,18,21,43,44 Similarly to our findings, Claes et al (2015) 18 observed a strong or moderate relationship between AFC and AMH concentrations in older resp. middle-aged mares, but, in contrast to our study, didn't find a correlation in young mares.…”

“…The observed values and the strong inter-individual variability in AFC and AMH concentration in mares are in line with published findings. 12,18,30,36,43 Similar variations were described for cows and women. 17,[45][46][47] The high positive correlation between AFC determined before and after ovulation indicates a high degree of reproducibility of the measurements by using two-dimensional B-mode sonography.…”

“…This could be explained by the relatively unequal distribution of mares between the different age groups in our study, but also by the previously reported large individual differences in follicular populations between individuals of the same age. 12,18,30,43,[45][46][47] In other species, other factors are known to affect AMH and/or AFC: in cattle and sheep, studies showed that maternal undernutrition during the first trimester has a negative impact on the AFC in the offspring. [55][56][57][58] Moreover, a study found that heifers from dams affected by chronic mastitis (clinical and subclinical) had lower AMH concentrations than their peers issued from healthy cows.…”

“…Diese Studie bestätigt den Zusammenhang zwischen AFC und AMH und eine hohe Repro- Fertility, AMH concentrations and AFC decline with age in all the aforementioned species, but there is a great variability of both AMH concentration and AFC even between individuals of the same age and therefore the onset of reproductive senescence associated with reduced ovarian reserve varies considerably. 8,12,15,18,21,30,[43][44][45][46][47] In some studies, no significant correlations between AMH and/or AFC and pregnancy rate have been reported in mares and women, indicating that besides the number of primordial follicles present in the ovaries and the AFC and AMH correlated to it, other factors such as oocyte quality are likely to play a role. [33][34][35] On the other hand, the study by Ball et al (2019) 12 demonstrated a relationship between AMH and fertility, which was reduced in mares with low serum AMH.…”