Estrus, ovulation, and serum progesterone, estradiol, and LH concentrations in mares after an increased photoperiod during winter.

The research investigates the influence of increased photoperiod on the estrus cycle, ovulation, and relevant hormone concentrations in mares during winter, suggesting that light treatment could induce earlier breeding and foaling in these animals.

Research Design and Experimentation

• The experiment involved 15 seasonally anestrous mares, which were randomly assigned on December 11, 1974, to one of three experimental groups: outdoor-control, indoor-control, and indoor light-treated.
• The indoor light-treated group was exposed to an extended 16-hour photoperiod. This setup continued until April 21, 1975.

Observations and Findings

• The mares from the indoor light-treated group ovulated notably earlier than those in the control groups. Specifically, ovulation in the light-treated mares occurred approximately 74 days earlier than in outdoor-control mares and 50 days earlier than in indoor-control mares.
• The duration of the first estrus varied among the groups, with the longest estrus observed in the indoor light-treated group and the shorted estrus in the outdoor-control group.
• The mares of the indoor light-treated group also averaged more estrous cycles before April 21 than the other groups.
• Typical hormone changes consistent with estrous cycle activity, including peak concentrations of luteinizing hormone and estradiol near ovulation and maximal progesterone levels during diestrus, were recorded in all mares beginning at the first estrus.
• Interestingly, hair loss occurred earlier in the light-treated mares than in the other groups, indicating a possible physiological response to the altered light conditions.

Conclusions

• The results indicated that introducing a 16-hour photoperiod in early December for anestrous mares could initiate normal estrous cycles within two months, leading to earlier breeding and foaling than typical.
• The increased photoperiod seems not only to affect reproductive behavior and physiology, but it may also influence other bodily processes, as suggested by the observed earlier hair loss in the light-treated group.
• Overall, this research presents a compelling argument for using controlled light exposure to manipulate breeding cycles in mares, potentially benefiting horse industries by enabling an earlier breeding period.