INFLUENCE OF TRAINING AND COMPETITION ON THE ENDOCRINE REGULATION OF TESTICULAR FUNCTION AND ON SEMEN PARAMETERS IN STALLIONS

The aim of this study was to determine the possible effects of perform ance training and participation in competitions on the fertility of br eeding stallions. Experiments were performed on 22 active breeding sir es divided into three groups: stallions used for breeding only (group 1), breeding stallions that took part in competitions regularly (group 2) and occasionally (group 3) during the breeding season which lasted from February to July. Blood samples were collected at 2-week interva ls and concentrations of LH, testosterone, oestradiol-17 beta and cort isol in plasma were measured by radioimmunoassay. During the period st udied, semen was collected regularly and the sperm concentration, moti lity and volume were determined. Testosterone release was significantl y higher in stallions that took part in competitions occasionally (gro up 3) than in the animals of the other two groups (p < 0.05). Plasma c ortisol concentrations of the stallions of group 3 were significantly higher than in the horses of the control group (group 1; p < 0.05). Sp erm motility of the sires of group 1 was significantly lower when comp ared to the horses of groups 2 and 3 (p < 0.05). No significant differ ences in concentrations of LH and oestradiol-17 beta in plasma as well as in semen volume between groups were found. All values remained wit hin the normal range and it is unlikely that training and competition had negative effects on fertility.