Pregnancy rates, LH and progesterone concentrations in mares treated with a GnRH agonist.

The study explores the impact of the GnRH agonist Buserelin, administered 10 days after ovulation, on the pregnancy rate of mares along with alterations in their progesterone and LH concentrations. It was found that the hormone did not significantly increase pregnancy rates while remarkably affecting LH concentrations.

Study Overview

• The research takes into account 191 warmblood mares subjected to two trials and utilized both fresh and frozen/thawed semen from 27 stallions for artificial insemination (A.I.).
• In trial A, out of the 171 mares, some were administered the GnRH agonist Buserelin (40 micrograms/animal) while the rest received 10 ml of 0.9% NaCl as a placebo.
• An ultrasound scanning of the uterus was carried out on day 16 post-A.I. to determine the pregnancy status. Four fixed factors (type of spermatozoa, treatment, A.I. number, mare’s reproductive status) and a random factor (stallion) were considered for statistical analysis.

Trial A Findings

• The Least Square Means (LSM) for pregnancy rates stood at 46.0% for Buserelin treated mares and 36.4% for the control group. The difference, however, was not statistically significant (P=0.22).

Trial B Overview and Findings

• In trial B, 20 lactating and cyclical mares underwent endocrine studies. From days 0 to 11, blood samples were taken to analyze progesterone and LH concentrations.
• Progesterone levels in both groups gradually increased from days 0 to 8 after ovulation. The concentrations from days 9 to 11 revealed no significant divergence between the GnRH and the control group.
• However, the GnRH agonist had a notable effect on LH concentrations. The hormone levels on day 10 were significantly higher in animals treated with the GnRH agonist than in those given the placebo.

Conclusion

• Based on the data obtained, it can be inferred that administering a GnRH agonist during the luteal phase could have varying effects on luteal function.

Conclusively, while the GnRH agonist Buserelin does not significantly enhance the pregnancy rate in mares, it does profoundly affect LH concentrations. Hence, its application in mare fertility protocols might need further investigation.