Reproductive parameters of breeding stallions in response to a moderate physical conditioning program

Abstract

Five breeding stallions, age 7 to I 1 years, were kept in confinement (stalls) with no exercise for an initial period of 60 days. A ten-day daily sperm output (DSO) determination was performed immediately before (pre-EP) and after (post-EP) an 8 wk forced exercise period (EP). Blood was collected hourly for a 6 h period the day prior to and the day after the end of the 8 wk EP. The exercise trial, performed in a 50 foot diameter roundpen, was as follows: each stallion was fitted with a heart rate (HR) monitor; walked for I min, trotted for 2 min, exercised until a HR of 165-180 beats per min was observed and then for an additional 5 min at that HR, trotted for a final 2 min; then walked for 30 min (electric horse walker) three times per wk for 8 weeks (Mon., Wed., Fri.). Additional exercise was received when they were walked for 30 min (electric horse walker) twice weekly (Sat., Sun.). Semen was collected for evaluation twice weekly during the 8 wk EP on the 2 d with no exercise (Tue, Thur.). Semen from the final 3 d of the two DSO determinations was analyzed for spermatozoal motility with a computer assisted spermatozoal motility analyzer, semen concentration, spermatozoal morphology, gel and get-free semen volume and total spermatozoa number, Pre-and post-EP values for individual stallions were compared and P < .05 was considered significant. Significant post-EP differences were observed for the percentage of progressively motile spermatozoa, total spermatozoal motility, percentage of morphologically normal spermatozoa, gel-free semen volume and mean blood plasma cortisol, LH and testosterone concentrations. A significant decrease in the percentage of morphologically normal spermatozoa and a significant increase in the percentage of abnormal midpieces was observed for stallions 1, 2 and 3 by d 8 after the initial day of exercise and by d 10 after the initial day of exercise for stallions 4 and 5.