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Embryo recovery from exercised mares

Mortensen, C.J., Choi, Y.H., Hinrichs, K., Ing, N.H., Kraemer, D.C., Vogelsang, S.G., Vogelsang, M.M.
Animal reproduction science 2009 v.110 no.3-4 pp. 237-244
mares, embryo transfer, female fertility, reproductive efficiency, exercise, ambient temperature, relative humidity, heat stress, physiological response, estrous cycle, follicular development, ovulation, conception, embryogenesis, embryo (animal), viability
The effect of exercise on mare reproductive efficiency was evaluated by comparing rates of embryo recovery from mares assigned to either an exercise regimen or a non-exercise (control) regimen. Exercised mares were worked daily for 30min under average ambient conditions of >30°C and >50% humidity. Mares were inseminated during estrus and subjected to uterine flush for embryo recovery on d 7 after ovulation for two consecutive cycles. After this, mares were allocated to the opposite group and allowed an estrous cycle without reproductive manipulation; then insemination and uterine flushing were conducted on two more consecutive cycles. Prostaglandin F₂α was administered on the day of uterine flush. Mare rectal temperature increased during exercise from a mean of 38°C to a mean of 39.9°C. Mares had ovulations from smaller follicles when exercised than they did under control conditions (39.8±0.5 compared with 41.5±0.5mm diameter; P <0.05), and had an increased time from PGF₂α administration to subsequent ovulation (8.47±0.337 compared with 9.27±0.294 d; P <0.05). Embryo recovery from control mares was 22 of 35 (63%). Fewer embryos were recovered from exercised mares (11 of 32, 34%; P <0.05). The proportion of embryos classified as Grade 1 tended to be less in exercised than in non-exercised mares (4 of 11, 36% compared with 16 of 22, 73%; P =0.051). These data indicate that exercising mares in a hot and humid environment are associated with changes in ovarian follicle development and ovulation, and a reduction in embryo recovery.