Serum anti-Müllerian hormone dynamics in mares following immunocontraception with anti-zona pellucida or -GnRH vaccines

Abstract

Circulating anti-Müllerian hormone concentration (AMH) is positively correlated to the number of small growing follicles in the mare and may reflect ovarian function. Dynamics of AMH during immunocontraception have not previously been investigated. This study aimed to compare serum AMH in mares following treatment with native porcine zona pellucida (pZP), recombinant pZP3 and pZP4 (reZP) or gonadotrophin releasing hormone (GnRH) vaccines, and saline-treated controls. Stored sera collected during two previous studies examining ovarian activity in mares during zona pellucida (ZP) or GnRH immunocontraception were analysed for serum AMH. Data were compared among treatment groups using mixed-effects linear regression and one-way ANOVA with post hoc testing. Correlations between AMH and previously reported clinical variables were estimated using Spearman's rho. Mares immunized against GnRH showed variable but detectable AMH throughout successive breeding and non-breeding seasons that were not significantly different to unvaccinated control mares. Mares treated with pZP demonstrated marked, reversible suppression of AMH. Mares immunized using reZP showed an intermediate effect. In the ZP study, AMH was positively correlated to serum progesterone concentrations, mean ovarian volumes and antral follicle counts, whereas no correlations between AMH and serum progesterone concentrations, mean ovarian volumes, or the presence of one or more follicles ≥20 mm in diameter were detected in the GnRH study. In conclusion, marked suppression of AMH during pZP immunocontraception, but not during GnRH immunocontraception, suggested enhanced suppression of ovarian follicular development and, or follicular function during pZP immunocontraception. Serum AMH concentrations may provide a novel tool for the assessment of ovarian function during ZP-based immunocontraception.

Ovarian function following immunocontraceptive vaccination of mares using native porcine and recombinant zona pellucida vaccines formulated with a non-Freund's adjuvant and anti-GnRH vaccines

“…However, AMH concentrations were correlated with ovarian volume and serum progesterone, suggesting that it can be useful under certain circumstances. Previous work by our research group noted the potential of serum AMH concentrations for monitoring ovarian function following immunocontraception in mares [24].…”

“…Samples were collected weekly from October to March in this previous work [19,24] but only analysed for five strategic time periods. The results of the previous study served to inform the frequency of sampling and study design for the current project.…”

“…However, populations requiring contraception are typically managed under extensive conditions and, therefore, practical methods with limited intervention opportunities are commonly required for monitoring effects [21]. Anti-Müllerian hormone (AMH) has been proposed as a tool for assessing ovarian function during ZP-based immunocontraception [24] as it is reportedly a consistent [25] and useful biological marker of ovarian function [26].…”

Anti-Müllerian hormone and ovarian aging in mares

“…The selective destruction of follicles at these stages of development in mice provides convincing evidence of this (Sahambi et al 2008). It is not clear what range of follicle populations might be targeted, but vaccination against porcine zona pellucida dramatically decreased AMH in mares (Joone et al 2018). As noted earlier, immunohistochemical analyses of equine ovaries suggest that AMH expression is higher in secondary and small antral than in large antral follicles (Ball et al 2008).…”

“…How quantitatively this reflects a decrease in follicle numbers is unknown. Recent observations on the response to immuno-contraception in mares indicated that vaccination against porcine zona pellucida also dramatically decreased AMH concentrations (Joone et al 2018). However, studies in reproductively seasonal species demonstrate that AMH is far from a perfect index of fertility and subject to considerable, unexplained individual variability (Roosa et al 2015).…”