Direct contact may affect the efficacy of stallion exposure in hastening the onset of cyclicity in anestrous mares.

The research attempts to assess the impact of exposure to a stallion on seasonal anestrous mares. The researchers’ objective was to check if direct or indirect exposure to a stallion could stimulate an increment in the Luteinizing hormone (LH) and quicken the first ovulation. However, the study concluded that such exposure failed to replicate the effects as observed in short-day breeders, and the induction of cyclicity in anestrous mares could depend on the duration of direct contact.

Research Methodology

• The study involved mares being grouped according to age and parity, and were randomly assigned to three treatments. – direct exposure (DXP), indirect exposure (IXP), and no exposure (control), each containing seven horses.
• In the DXP treatment, mares were housed next to the stallion and allowed direct contact for two hours, three days a week. For this, the stallion was placed into a cage at the center of a tease pen.
• The IXP treatment had mares housed in a pen adjacent to the stallion but without any direct contact.
• In the control group, mares were kept away from the stallion with no direct or indirect contact.
• On the first, third, and fifth days of the treatment, blood was collected hourly for eight hours for measurements of LH and prolactin (PRL) concentrations.
• The hormone concentrations were analyzed as repeated measures, and the time from the beginning of the treatment to ovulation was analyzed using one-way ANOVA.

Findings of the Study

• The study did not find a significant difference in the time from treatment initiation to first ovulation among the different groups.
• However, among the DXP mares, it was observed that the socially dominant mares ovulated sooner than socially subordinate mares.
• No significant differences were found in the LH concentrations among the different treatments, but there was an increase in concentration over the course of the treatment.
• The levels of PRL were higher in the IXP group compared to the DXP and control groups, regardless of the day of treatment.
• PRL concentrations were also found to be higher on the third day of treatment compared to the first and fifth days of treatment.

Conclusion

• Contrary to what was observed in short-day breeders, the study concluded that direct or indirect exposure of anestrous mares to a stallion failed to induce the same effects.
• The study suggests that the effect of stallion exposure on the onset of cyclicity in anestrous mares may be dependent on the duration of direct contact.