Infusion of gonadotrophin-releasing hormone (GnRH) induces ovulation and fertile oestrus in mares during seasonal anoestrus.

The research investigates the impact of gonadotrophin-releasing hormone (GnRH) infusion in inducing ovulation and fertile oestrus in female horses during seasonal anoestrus. The study demonstrates that a continuous infusion of GnRH induces ovulation in mares, which can potentially aid in controlled breeding practices.

Research Methodology

Two experiments were conducted:

• In Experiment 1, 30 Standardbred mares, which were in deep seasonal anoestrus, were divided into three groups, including a control group and two groups treated with different GnRH doses (50 ng and 100 ng). The treatment was administered for 28 days via osmotic minipumps. The researchers evaluated ovulation frequency, plasma GnRH profiles, and LH pulse frequencies.
• Experiment 2 involved 27 Standardbred mares in shallow seasonal anoestrus, with part receiving no treatment and part receiving GnRH infusion (100 ng) over the same period. Here, mares were mated during the oestrus period and measurements included the time of ovulation and conception.

Research Findings

The results from both experiments indicated that:

• In the first experiment, a higher ovulation rate was noted in mares treated with GnRH than in the control group. The plasma profiles and LH concentrations, which relate to ovulation, were found to be dose-dependent.
• The untreated mares had a steady decline of LH after initial rise whereas the treated mares that ovulated had biphasic LH concentrations. The treated group also showed an increase in LH pulse frequency.
• In the second experiment, mares treated with GnRH ovulated and conceived earlier than the untreated group. The only mare that didn’t conceive was in the untreated group.
• The findings together indicate that constant GnRH infusion can induce ovulation and fertile oestrus in mares during both deep and shallow seasonal anoestrus. Both ovulation and conception times were significantly earlier in treated mares than untreated mares.

Implications of the Research

These findings suggest that GnRH infusion could be an effective method for inducing ovulation in mares during their non-breeding season (seasonal anoestrus), which could be of significant value to horse breeding utilities and industries. However, further research is needed into the long-term effects and potential side effects of GnRH infusion, as well as more detailed comparisons of efficacy between varying dosages.