Reproductive physiology of the stallion. VIII. Artificial photoperiod, collection interval and seminal characteristics, sexual behavior and concentrations of LH and testosterone in serum.

This research investigated the impact of artificial photoperiods on the reproductive physiology of stallions. The findings revealed that exposure to an artificial photoperiod affected semen quality, sexual behavior, and hormone concentrations, but no influence was found on the total quantity of sperm or its motility.

Subject and Methodology

• This study focused on stallions subjected to artificial photoperiods, a method where the natural light and darkness sequence is altered.
• The experiment began on October 15, 1973, with an incremental increase in artificial daylight hours, reaching a maximum of 16 hours per day by February 8, 1974. This new schedule was maintained till October 6, 1974.
• The semen from five treated and four control stallions was collected twice a week with alternating time intervals: 24 hours and 1 hour on subsequent weeks.

Findings on Seminal Characteristics and Sexual Behavior

• Exposure to the artificial photoperiod resulted in lesser amounts of gel-free semen and gel per ejaculate during the summer season. Nonetheless, the sperm concentration in the gel-free semen was higher compared to untreated stallions.
• No consistent differences were observed concerning the total number of spermatozoa per ejaculate or percentage of moving sperm cells under the artificial photoperiod.
• The artificial photoperiod did reduce the stimulation time, i.e., the time taken for an animal to reach ejaculation, in late winter, but it didn’t affect the number of mounts per ejaculate or seminal pH.

Impact on Hormone Concentrations

• The study found variances in serum LH (Luteinising Hormone) levels over time in untreated stallions, often showing a seasonal pattern. Nevertheless, there was no corresponding change observed in the concentrations of testosterone.
• Both LH and testosterone concentrations were observed to be significantly higher in the serum of stallions subjected to artificial photoperiods during winter as compared to the controls.

Significance of Collection Interval

• First and second ejaculates demonstrated significantly different characteristics for the 1-hour and 24-hour collection intervals, except sperm motility.
• The 24-hour interval showed no difference in mounts per ejaculate.
• The characteristics of the first ejaculates were unaffected by the collection interval, but the second ejaculates showed differences in all properties except for sperm motility.