Hormonal levels and semen parameters of Criollo breed stallions under intensive training

Abstract

The stress associated with intensive training may reduce reproductive efficiency in Criollo stallions. The objective was to compare semen quality and cortisol, testosterone, and estradiol levels in Criollo stallions under training conditions with those of stallions under regular field conditions. Criollo breed stallions (n¼18) were evaluated from August 15th to October 30th. The Exercise group (ExG, n¼9) received one hour of exercise per day, and participated in competitions during the experimental period. The Control group (CoG, n¼9) neither exercise nor participated in competition. Before the initiation of the experiment, semen was collected by artificial vagina twice a day for 7 consecutive days to keep the stallions in daily sperm output (DSO). Every 15 days semen (2 separate ejaculates an hour apart) and serum samples (before and after exercise in ExG) were collected. Analysis of variance using repeated measures (SAS System) with stallions nested in treatments and day as repeated factor was used to evaluate the results. There was no effect of exercise in testosterone levels (pre-exercise: 0.58 0.06 ng/mL, post-exercise: 0.66 0.06 ng/mL, CoG: 0.50 0.06 ng/mL; P¼ 0.28) and estradiol levels (pre-exercise: 222.17 36.23 pg/mL, post-exercise: 228.84 36.23 pg/mL, CoG ¼ 231.91 36.08 pg/mL; P¼0.97). However, in the ExG cortisol level was higher after exercise (pre-exercise 59.96 4.58 nM/mL vs. posexercise 81.05 4.58 nM/mL) while in the CoG cortisol level was 59.80 4.57 nM/mL (P¼0.004). There was an effect of exercise on the following semen parameters: gel-free volume (ExG 41.46 6.1 ml vs. CoG 53.33 6.3 ml; P<0.001), sperm motility (ExG 47.8 2.53 % vs. CoG 63.56 2.5 %; P <0.0001), total number of sperm (ExG 8104.91 1267.16 x 106 vs. CoG 12124.16 1252.58 x 106 ; P¼ 0,0001), normal sperm morphology (ExG 60.03% 1,69 vs CoG 76.73% 1.67; P < 0.0001) and total number of morphologically normal and motile sperm (ExG 2277.65 564.2 x 106 vs. CoG 5730.54 557.3 x 106 ; P<0.001). No effect of exercise was found in color, pH, sperm concentration. The study showed that exercise under this experimental condition had a negative impact on seminal quality. Nevertheless, semen parameters remained within the normal ranges established for stallions.