Influences of season and artificial photoperiod on stallions: luteinizing hormone follicle-stimulating hormone and testosterone.

This research investigates the seasonal and artificial light effects on the reproductive hormones — luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone — in stallions.

Research Methodology

• The researchers grouped stallions into seven per group and subjected them to three different treatments. The first group was exposed to natural day length as the control group.
• The second group was subjected to 8 hours of light and 16 hours of darkness (8:16) for 20 weeks, starting July 16, 1982, and then 16:8 from December 2, 1982, until March 5, 1984 (represented as S-L).
• The third group received 8:16 from July 16, 1982, until March 5, 1984 (represented as S-S).
• Blood was sampled hourly for five hours every four weeks; sera were pooled within each horse, and the concentrations of LH, FSH, and testosterone were quantified.
• Additionally, blood was collected every 20 minutes for 24 hours every eight weeks and two weeks before and after the December light shift. Samples were assayed for LH.

Results and Findings

• The results showed that stallions in all groups exhibited seasonal changes in the concentrations of LH, FSH, testosterone, and basal concentrations of LH and amplitude of LH pulses.
• The severity of said changes was influenced by the treatment they received (S-L or S-S), as observed in the significant season X treatment interaction.
• An earlier recrudescence (renewed growth or activity) of LH, FSH, and testosterone concentrations was observed in S-L stallions, followed by earlier regression. FSH hormone concentrations, however, were depressed in S-S stallions.
• The number of LH pulses per 24 hours was unaffected by the season, treatment, or their interaction.
• There was a significant effect on the basal concentrations of LH due to season X treatment interaction. The mean amplitude of LH pulses was also affected, with maximal values occurring in April versus February for control and S-L stallions, and minimal values occurring in December versus April.

Conclusion

• The findings from this study indicate that seasonal changes in reproductive hormone concentrations (LH, FSH, and testosterone) in stallions can be influenced by photoperiod.
• Furthermore, increased peripheral concentrations of LH during seasonal recrudescence of reproductive function appear to result from more LH secreted per discharge without an increased frequency of LH discharges.