[The effect of the season and sexual stress on the concentration of testosterone and estradiol-17beta in the seminal plasma of stallions].

This research paper investigates how seasonal changes and sexual activity influence the levels of testosterone and estradiol-17beta in the seminal plasma of horses. The study shows that the reproductive hormone levels and semen properties in stallions are impacted by seasonal variations and ejaculation frequency, suggesting hormones such as testosterone and estradiol-17 beta may be attached to sperm or gather in the seminal fluid.

Study Methodology and Variables

• Three stallions acted as the subjects of the study, contributing semen samples weekly for a period of six months from December to May.
• Certain parameters of semen (volume, gel-free volume, and sperm concentration) and the hormones testosterone and estradiol-17 beta were evaluated.
• Additionally, once a month, three ejaculates were obtained from each stallion at one-hour intervals and thoroughly examined.
• The testosterone and estradiol-17 beta levels were also measured in the stallions’ peripheral blood plasma collected twice a week.

Key Findings

• The parameters of the semen (volume, gel-free volume, and sperm concentration) showed clear variation based on the season.
• The testosterone level was at its lowest in December in the peripheral blood plasma but gradually increased in the seminal plasma throughout the experimental period.
• However, testosterone levels in the seminal plasma were only one-tenth of those in peripheral blood plasma.
• The concentration of estradiol-17 beta was found to be highest in April and May in blood plasma, while its levels in the seminal plasma showed no significant changes.
• The collection of three successive ejaculates led to a significant decrease in both the volume of the ejaculate and sperm concentration.
• The testosterone level in seminal plasma remained unaffected by ejaculation frequency, but the concentration of estradiol-17 beta decreased significantly in the second and third ejaculates.
• The collected data suggest that estradiol-17 beta in stallion semen may be bound to spermatozoa, or it accumulates in the seminal plasma.