Assessment of anti-Müllerian hormone in mares’ transitional period and in relation to fertility in elderly mares.

This research article attempted to evaluate whether Anti-Müllerian Hormone (AMH), a reproductive hormone, could be used as a biomarker to predict two conditions in mares: the onset of cyclicity (their reproductive period), and fertility in middle-aged mares. However, the study found no significant difference in AMH concentrations before and after the first ovulation of the reproductive period and did not find a link between AMH concentrations and early pregnancy rates in mares.

Study Design & Methodology

The research engaged in two primary evaluations:

• The first part of the study focused on using plasma AMH as an early indicator of the onset of cyclicity in mares transitioning from the non-reproductive (anovulatory) phase to the reproductive (cyclic) phase. Ten mares aged between 8 to 17 years were involved in the experiment, observed from the middle of February until the end of April. Ovarian activity was monitored using ultrasonography, documenting the presence of a corpus haemorrhagicum/luteum and noting antral follicle counts. Blood samples were taken weekly to track AMH concentrations before and after the first ovulation of the year.
• The second part of the study aimed at determining if plasma AMH concentrations in middle-aged mares (12 to 21 years) were associated with fertility. Forty-one mares were inseminated with either fresh or frozen semen, while a variety of factors were analysed regarding their potential associations with the ‘early pregnancy rate’ through logistic regression models. These factors considered AMH concentrations, age, mare status, stud, development of post-breeding endometritis, number of inseminations and semen type.

Research Findings

The findings from the two parts of the study were:

• In the first evaluation, a correlation was observed between AMH and antral follicle counts for the entire study period, as well as prior to and after the first ovulation. However, there was no statistical difference in AMH concentrations before and after the first ovulation, contradicting the hypothesis that AMH could potentially signal the onset of cyclicity in mares.
• The second evaluation did not find any association between the early pregnancy rate and AMH concentrations, nor any of the other factors considered. Therefore, the research did not support the idea of utilizing AMH as a prognostic marker for fertility in middle-aged mares.

Conclusions

The study does not support the use of AMH as a predictive biomarker for either the onset of cyclicity or fertility in mares. The AMH concentrations showed no significant difference before and after the first ovulation of the breeding season. Additionally, no relationship between AMH concentrations and early pregnancy rates was observed, counteracting the initial hypothesis of the research.