Anti-Müllerian Hormone Predicts Follicular Reserve in Aged Mares

Follicular reserve (measured as antral follicle count; AFC) declines with mare age. Determination of serum anti-Müllerian hormone (AMH) concentrations is highly correlated with follicular reserve in older mares, and AMH determination may be useful to assess the reproductive longevity of older mares. Authors’ addresses: Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546-0099 (Claes, Ball, Scoggin, Esteller-Vico, Kalmar, Squires, Troedsson); and Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616 (Conley); email: b.a.ball@uky.edu.

1. Introduction

The number of follicles remaining in the ovary (follicular reserve; AFC) declines with age in mares until reproductive senescence is reached but at variable ages. Anti-Müllerian hormone is produced by small follicles, and circulating concentrations of AMH have been used to measure follicular reserve in other species. The objective of this study was to examine the relationship between AMH and AFC in mares of different ages.

2. Materials and Methods

Young (3–8 years; n = 10), middle-aged (9–18 years; n = 16), and old (>18 years; n = 19) mares were examined by transrectal ultrasonography, and all antral follicles were counted (AFC) across multiple estrous cycles. Plasma AMH concentrations were measured by ELISA across multiple estrous cycles. Data were analyzed by nonparametric correlation. 

3. Results and Discussion

AFC was lower in old compared to middle-aged or young mares. The repeatability of AFC and AMH was high within and across estrous cycles. Overall, AFC was positively associated with plasma AMH concentrations although this relationship was influenced by age. The relationship between AFC and AMH for aged mares (ρ = 0.86; P < 0.0001) and middle-aged mares (ρ = 0.60; P = 0.01) was greater than the correlation between AFC and AMH in young mares (ρ = 0.40; ns). Plasma AMH concentrations are predictive of antral follicle counts in older mares and may be useful to assess follicular reserve as well as reproductive longevity.

Acknowledgments

The authors thank Minitube of America® for providing the AMH ELISA. We also thank Dr. E. Woodward, C. Fedorka, and Dr. G. Davolli for their assistance with the clinical part of this research project. Funding for this project was provided by the Albert G. Clay Endowment of the University of Kentucky.

Conflict of Interest

Dr. Troedsson has a professional affiliation with MOFA^TM, Minitube of America.