Prolactin administration to seasonally anestrous mares: reproductive, metabolic, and hair-shedding responses.

This research study investigated the potential of prolactin hormone administration to incite reproduction, metabolic changes, and hair shedding in mares that are seasonally anestrous (not in heat). It was observed that prolactin hormone induced hair shedding, provoked estrus (heat), and expedited the first ovulation among the tested mares.

Research Methodology and Participants

• The research was conducted on 16 pony mares. Eight of them were subjected to a daily dose of 4mg of recombinant porcine prolactin (rpPRL) for 45 days starting on January 15. The other eight mares were used as a control group and were administered a vehicle solution.
• The scientists monitored the mares for reproductive patterns, metabolic indicators, hair shedding, and thyroid activity.

Results and Findings

• Prolactin concentrations in the mares treated with rpPRL reached a peak of 94 ± 19 ng/mL two hours after injection and leveled down to 5.1 ± 1.7 ng/mL 24 hours after injection.
• Administration of the rpPRL enhanced hair shedding within 14 days, reaching a peak at 28 days and then drastically declining.
• Studies confirmed the existence of antibodies in the rpPRL-treated mares by the 28th day, justifying the termination of data collection at this point.
• The prevalence of mares in estrus (heat) after 17 days of treatment was higher for mares treated with rpPRL compared to the controls. However, the onset of estrus didn’t deviate much within both the groups.
• Prolactin administration advanced the date of first ovulation, as determined by plasma progesterone levels. The mean date for treated mares was February 6 ± 3 days, whereas for control mares, it was March 14 ± 6 days.
• There were no significant impacts observed on concentrations of insulin-like growth factor I and nonesterified fatty acids over time.
• Minimal discrepancies were seen in thyroid hormone secretion between the rpPRL treated mares and the control group.
• Prolactin treatment did not significantly affect glucose and insulin levels in the mares.

Research Conclusion

• The research concludes that the prolactin hormone plays a key role in initiating the spring shedding of hair in mares and somehow participates in the ovulation process.