Exercise affects both ovarian follicular dynamics and hormone concentrations in mares D.E. Kelley a,b, *, J.R. Gibbons b , R. Smith b , K.L. Vernon b , S.E. Pratt-Phillip c , C.J. Mortensen a,b a Department of Animal Sciences, University of Florida b Department of Animal and Veterinary Sciences, Clemson University c Department of Animal Sciences, North Carolina State University Received 17 June 2010; received in revised form 24 February 2011; accepted 11 March 2011 Abstract The objectives were to evaluate the effects of exercise on ovarian folliculogenesis and related hormones in mares. Mares (n = 11) were randomly assigned into a control (non-exercised) or treatment (exercised) group. Treatment mares (n = 5) were moderately exercised for 30 min, 6 d/wk. All mares underwent daily transrectal ultrasonographic examinations and ovarian follicles  6 mm were measured. Blood samples were collected during the first (Cycle 1) and last (Cycle 4) cycle, and serum concentrations of cortisol, LH, and FSH were determined. Mean cortisol concentrations were elevated (P  0.05) in exercised mares, 6.29  0.22 compared with 5.62  0.16 ng/dL (mean  SEM), 30 min post exercise. There were no significant differences between groups in mean FSH concentrations; however, exercised mares had lower (17.3  6.4 vs 41.1  5.5 ng/mL; P  0.05) peak LH concentrations. Furthermore, exercised mares experienced a longer (24.7  0.8 vs 22.2  0.8 d; P  0.05) mean interovulatory interval for all cycles combined, fewer (P  0.05) follicles 6 to 20 mm in diameter, and an increased (P  0.05) number of follicles 20 mm following deviation. The dominant and largest subordinate follicle in exercised mares had a greater (P  0.05) mean diameter on the day of deviation, suggesting delayed deviation. Exercised mares also tended (P = 0.06) to have an increased number of cycles with at least two dominant follicles compared to control (62 vs 36%, respectively), indicating a decreased ability of the largest follicle to assert dominance. Under the conditions of this study, moderately exercising mares induced higher cortisol concentrations, lowered peak LH concentrations, and altered ovarian follicular dynamics. © 2011 Elsevier Inc. All rights reserved. Keywords: Exercise; Ovarian follicular development; Follicle deviation; Mare; Horse 1. Introduction Increasingly, equine organizations are allowing mul- tiple registries per mare per year. Subsequently, this allows valuable performance mares to both compete and produce offspring with the assistance of embryo transfer, or other assisted reproductive techniques. Ev- idence is mounting that mares in competition during the breeding season produce fewer embryos and/or fail to conceive. Sertich [1] reported (4 y study interval) an embryo recovery rate of 40.5% with performance mares in training and competition, whereas typical em- bryo recovery rates of non-exercised mares ranged from 50 to 75% [2,3]. In another study, Mortensen et al [4] reported mares exercised daily for 30 min under hot and humid conditions had a significantly reduced em- * Corresponding author. Tel.: 352 392 0133. E-mail address: dekelle@ufl.edu (D.E. Kelley). Available online at www.sciencedirect.com Theriogenology 76 (2011) 615– 622 www.theriojournal.com 0093-691X/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.theriogenology.2011.03.014