Effects of Strenuous Exercise on Stallion Sperm Quality
Rosenberg, Jennifer L.
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Some stallions are expected to perform athletically and breed contemporarily. Athletic activity has the potential, especially during the summer months, to induce thermal stress to the testes, resulting in reduced reproductive capability due to decreased sperm quality and libido. There is concern in the horse industry about what level of exercise, if any, affects the reproductive capability of a stallion. Thermal stress associated with training and exercise may impact sperm quality and the future reproductive capability of the stallion. The goal of this study was to determine the effect of strenuous exercise on stallion sperm quality. The objectives were to measure changes in body and scrotal temperatures following strenuous exercise and sperm quality following strenuous exercise. Miniature Horse stallions (n = 7), implanted with subdermal thermosensory devices in the subcutaneous neck and scrotal tissue, were assigned to treatment group based on age and semen quality. Exercising stallions (EX; n = 3) were exercised 4 d/wk for 90 min for 12 wk, while non-exercising stallions (CN) were tied in the shade. Semen was collected from stallions for 5 consecutive days every 4 wk to evaluate semen quality (raw, 24 h and 48 h cooled). Subcutaneous scrotal (SQST), rectal (RT) and neck (NT) temperatures were recorded along with heart rate. Spermatozoa data were normally distributed; therefore, they were subjected to parametric analysis by repeated measures (wk) using the PROC MIXED procedure (SAS v 9.1; SAS Inst. Inc., Cary, NC). Model included treatment (CN or EX), time (wk 0, 4, 8, or 12), and stallion as the subject of the repeated measures. Compared to the CN group, EX stallions had elevated temperatures (avg RT 39.27 vs 37.07 degrees, NT 39.77 vs 37.44 degrees C, and SQST 34.90 vs 33.40 degrees C; P < 0.0001). There was no difference in sperm quality between treatment groups (P > 0.05). In this study, strenuous exercise in Miniature Horse stallions, did not affect sperm quality. This suggests that anecdotal reports of reduced sperm quality in stallions in training may have other causes other than elevated scrotal and body temperature. While previous studies have illustrated that prolonged insulation of the testes reduces semen quality, strenuously exercising stallions for up to 90 min under hot and humid ambient conditions may not be harmful to spermatogenesis.