Enzymatic scavengers are equally present in stallion testis and epididymis

Abstract

collection has not been studied. As sexual arousal, mounting of the dummy and ejaculation involve both physical and emotional activity, we hypothesized that semen collection would induce a pronounced stress response. Experiments were performed on two consecutive days using adult experienced breeding stallions (n 1⁄4 16; mean age 6.3 0.7 years) in a semen collection center. Continuous cardiac beat–to-beat interval recordings were made from 30 min before to 30 min after semen collection and were analysed at 1 min-intervals. Saliva for cortisol analysis was collected repeatedly from 60 min before to 120 min after collection of semen. Statistical comparisons were made by ANOVA using a general linear model for repeated measures with day as between subject factor. Semen collection resulted in a significant increase of heart rate (HR) but no differences between experimental days were seen (30 min before semen collection day 1: 36.6 2.3, day 2: 33.4 1.7 beats/min; at semen collection day 1: 94.5 5.1, day 2: 96.1 4.1 beats/min; differences over time P < 0.001, no significant interactions between time and day). In parallel, a significant decrease of the heart rate variability parameter RMSSD (root mean square of successive beat-to-beat differences) was seen reflecting a decrease in vagal activity (30 min before semen collection day 1: 105.9 10.0, day 2: 114.4 11.2 ms; at semen collection day 1: 75.1 8.8, day 2: 61.3 8.1ms; differences over time P < 0.001, no significant interactions between time andday). Values ofHR andRRSMDreturned to baseline values within 15 min after semen collection. No significant changes in salivary cortisol occurred (30 min before semen collectionday1: 1.8 0.2, day2: 1.9 0.2ng/ml,15minafter semen collection day 1: 2.4 0.5, day 2: 2.0 0.2 ng/ml, no significant differences over time, no significant interactions between time and day). In conclusion, breeding stallions respond to the collection of semen with a transient stress response. This is not reflected in salivary cortisol release; however, baseline cortisol concentrations are considerably higher than in stallions not used for breeding. This suggests that in active sires during the breeding season, a continuous activation of adrenal function is present reflecting chronic stress. Thus, at least in individual stallions, stress effects such as impaired immune function cannot be excluded and may contribute to reduced fertility.