2010 American Registry of Professional Animal Scientists. In the stallion, inconsistent sexual behavior and variable semen quality are common, and this variability has been attributed, in part, to differences in circulating hormone concentrations. The objectives of this study were to quantify blood plasma concentrations of testosterone (TE), cortisol (CO), and estrone sulfate (ES) around the time of ejaculation, and to determine potential correlations with sexual behavior and sperm characteristics. Results indicate that both ES and CO increased (P < 0.05) at the time of semen collection, whereas TE did not increase. Estrone sulfate (r = -0.42, -0.34, and at times -15, + 30, and + 60, respectively) and the ratio of ES to (r = -0.41, and -0.39 at -15, + 30, and + 60, respectively) were negatively correlated with libido scores at multiple times around ejaculation (P < 0.05). Additionally, a positive relationship was found between ES and reaction time (r = 0.41 and O.35 at -15 and + 60, respectively), as well as between CO and libido scores (r = 0.38 and 0.45 at times -15 and + 15, respectively; P < 0.05). No relationship was observed between TE and sexual behavior; however, TE was positively correlated with progressive motility (r = 0.40), whereas the ES:TE ratio was negatively correlated with progressive motility (r = -0.35; P < 0.05). No other association was detected between the ejaculate parameters and hormone concentrations analyzed. These results further characterize the hormone profiles of stallions around the time of ejaculation while providing additional insight into the potential interaction the endocrine system may play in relation to stallion sexual behavior and sperm production.
The Professional Animal Scientist