[Follicular dynamics after treatment with hCG for ovulation induction in mares].

The research article explores the effects of utilizing human chorionic gonadotropin (hCG) in helping mares ovulate, particularly focusing on factors like the follicle’s diameter at the moment of hCG administration, the subsequent follicular growth, and the rate of double ovulations.

Study Background

• The human chorionic gonadotropin (hCG) hormone is known for its capacity to induce ovulation. The researchers aim to study its effectiveness and impact on mares displayed for artificial insemination.
• Follicular dynamics, such as the size of the follicle at the time of hCG administration and follicular growth post-hCG, are significant factors the scientists paid attention to.
• Moreover, the study also investigated the rate of double ovulations – a rare phenomenon where two eggs are released in one cycle.

Experimental Setup

• 168 mares undergoing estrous periods were subjected to this treatment. The treatment consisted of administering hCG to the mares. 249 estrous cycles were observed.
• hCG was given when a minimum follicle diameter of 30mm was detected via ultrasonography, alongside a developed edema (swelling) within the endometrium.
• The mares’ reaction times to the hCG treatment were recorded, with particular focus on when the ovulation occurred – within 24 hours, 24 to 48 hours, or beyond 48 hours after hCG administration.

Findings and Conclusions

• In nine estrous periods, ovulation occurred within 24 hours after hCG treatment. Majority of the mares (216 out of 249; 86.7%) ovulated between 24 to 48 hours, and in 24 cases, ovulation was delayed beyond 48 hours.
• There was no significant influence of follicle size at the hCG treatment time on the percentage of mares ovulating between 24-48 hours. This was similar across the varying follicle size brackets (89.2% for 30-34mm, 87.9% for 35-39mm, and 83.7% for 40mm and above).
• Double ovulations were observed in 17.7% of estrous periods.
• The pregnancy rate after one cycle was not significantly influenced by the follicle size at hCG administration.
• Repeated treatments with hCG during successive estrous cycles within a year did not alter the response rate to hCG.
• The results suggest that mares in standing estrous respond optimally to hCG if a minimum follicle size of 30mm and a well-developed endometrial folding are present.