Evidence for quadratic association between serum anti-Müllerian hormone (AMH) concentration and fertility in dairy cows

Highlights

• AMH concentration did not have linear association with reproductive parameters of dairy cows.

• AMH concentration had quadratic relationship with reproductive performance of dairy cows.

• Cows with minimal and maximal levels of AMH had inferior fertility than their counterparts with moderate levels of AMH.

Abstract

In cattle, results of some but not other studies indicated there has been an association of circulating anti-Müllerian hormone (AMH) concentration with reproductive variables. Considering the inconsistency in results among previous studies, there was evaluation of associations between circulating AMH and reproductive performance in dairy cows, and to this end, the prevailing data of serum AMH concentration and reproductive variables were used (n = 172). Preliminarily, association of AMH concentration with reproductive indices were analyzed using linear and quadratic models. Subsequently, cows were categorized based on AMH concentrations in four equal quartiles, including cows with the least (Q₁; n = 43), moderately lesser (Q₂; n = 43), moderately greater (Q₃; n = 43) and greatest (Q₄; n = 43) AMH concentrations, and reproductive variables were compared among the respective AMH quartiles. Initially, assessments indicated reproductive variables were not linearly associated with serum AMH (P > 0.05); however, for all reproductive variables except days to first breeding service (DFS) there was a quadratic association with serum AMH (P < 0.05). Results from analysis of reproductive performance in various AMH quartiles indicated there was a longer period of DFS for cows in Q₃ than Q₁ (P < 0.05). First postpartum insemination to conception and calving to conception intervals were shorter for cows in Q₃ than Q₁ and Q₄ (P < 0.05) and for cows in Q₂ than Q₁ (P < 0.05). In conclusion, results from the present study indicate cows with intermediate AMH concentrations had greater reproductive performance.

Introduction

Anti-Müllerian hormone (AMH) is a dimeric glycoprotein, which belongs to the transforming growth factor β (TGF-β) family of growth and differentiation factors (Cate et al., 1986). During sexual development of the embryo, AMH, which is produced by Sertoli cells in testes of male embryos, has important functions in regression of paramesonephric ducts in the male embryos, whereas in female embryos, absence of AMH would lead to development of paramesonephric ducts to female reproductive organs (Jost, 1947; Josso et al., 1993). With further embryo/fetal development, there would be initiation of AMH secretion from granulosa cells of ovarian follicles in the females of various species including cattle (Takahashi et al., 1986), sheep (Bézard et al., 1987), mice (Ueno et al., 1989; Durlinger et al., 1999) and humans (La Marca and Volpe, 2006). The production of AMH initiates when activation of primordial follicles occurs, with maximal secretions from preantral and small antral follicles and there is a subsequent decrease in secretion from follicles that develop to the antral stage (McGee and Hsueh, 2000; Weenen et al., 2004; Monniaux et al., 2008; Mossa et al., 2017). In terms of functions, AMH inhibits primordial follicle activation and attenuates the stimulatory effect of FSH on follicular growth; therefore, it is believed that AMH contributes to preservation of ovarian primordial follicle reserve pool, and in turn, extension of reproductive lifespan in females by suppressing the early depletion of primordial follicles from the ovarian pool and inhibiting development of activated follicles (Durlinger et al., 1999, 2001; Dewailly et al., 2014; Mossa et al., 2017).

Irrespective of AMH biochemical and biological properties, this hormone has been recognized to be associated with antral follicle count (AFC; Ireland et al., 2008; Rico et al., 2009; Baldrighi et al., 2014; Gobikrushanth et al., 2017), and both of these biological variables are considered as reliable indirect markers for size of ovarian primordial follicle reserve pool in cattle (Ireland et al., 2008; Tenley et al., 2019) and other species including humans (La Marca and Volpe, 2006). The AMH concentration, therefore, has been evaluated to assess effects of various factors on the ovarian primordial follicle reserve pool in different studies (Mossa et al., 2013; Akbarinejad et al., 2017, 2018). Furthermore, considering the relationship between AMH and size of ovarian reserves and the extent of repeatability of AMH concentrations among individuals (Ireland et al., 2008, 2011; Rico et al., 2009, 2011, Ribeiro et al., 2014; Souza et al., 2015; Gobikrushanth et al., 2017), a number of studies have been conducted to evaluate the association of circulating AMH concentration with reproductive performance of cows so as to understand whether a single assessment of circulating AMH could serve as a predictor of fertility in cattle (Ribeiro et al., 2014; Baruselli et al., 2015; Jimenez-Krassel et al., 2015; Gobikrushanth et al., 2018, 2019). Rebeiro et al. (2014) reported that AMH concentration was positively associated with pregnancy rate when cows were inseminated based on observation of spontaneous estrus. Furthermore, Jimenez-Krassel et al. (2015) reported that fewer cows with the least concentration of AMH were pregnant considering all lactation periods and there was a lesser retention in the herd of these cows as a result of culling practices. More recently, Gobikrushanth et al. (2019) reported that there were lesser pregnancy rates of cows with the least plasma AMH concentration. Nevertheless, results of other studies indicate there is no relationship between blood serum/plasma AMH concentrations and reproductive performance in cattle (Baruselli et al., 2015; Gobikrushanth et al., 2018). Considering these inconsistences in results among studies in terms of the association between concentration of circulating AMH and fertility of cows, there was assessment, in a retrospective study, of the associations between serum AMH concentration and reproductive performance in dairy cows using both linear and quadratic statistical models.