Seasonal and circadian changes of testosterone levels in the peripheral blood plasma of stallions and their relation to semen quality.

Abstract Summary: The study investigates the effect of seasonal and daily changes on testosterone levels in stallions and how it correlates with the quality of semen. It found that testosterone levels were highest in summer but semen quality was optimum in autumn, suggesting a lack of direct association between the two.

Study Design and Procedure

• The research was based on three stallions, studied over one year.
• Each stallion was bled every hour for a span of 25 hours at regular intervals of 28 days.
• Testosterone levels were subsequently measured and recorded.

Findings on Testosterone Levels

• Testosterone levels fluctuated in a pulsatile manner.
• Both pulse frequency and pulse amplitude were observed to be higher during the summer months in comparison to other seasons.
• The number of testosterone pulses varied throughout the day. They were most frequent in the afternoon (14:00-17:00 hours) and at night (22:00-01:00 hours).
• The overall mean testosterone levels were found to be highest in the summer.
• A secondary, smaller increase in testosterone levels was noted in the autumn season.

Findings on Semen Quality

• Semen characteristics were analyzed and measured from a wide sample of 222 stallions.
• The volume of semen was found to be greatest in the summer.
• The concentration of spermatozoa and the total number of spermatozoa per ejaculate were noticed to be highest in the autumn.

Conclusion of the Study

• The study showed that the highest testosterone concentrations in the blood plasma did not coincide with the best quality of semen.
• This indicates that there may not necessarily be a direct association between testosterone levels and semen quality in stallions.