Initiation of superovulation in mares 5 or 12 days after ovulation using equine pituitary extract with or without GnRH analogue.

The research focused on the impact of beginning superovulation treatment in mares either 5 or 12 days after ovulation, using equine pituitary extract (EPE) either alone or in combination with a GnRH analogue. It found that starting the treatment at day 5 resulted in more ovulation, and using the GnRH analogue showed slight enhancement in response to the EPE treatment.

Experimental Groups and Treatments

• The study involved three groups each with 15 cyclic mares. Each group was subjected to slightly different treatment methods.
• Group 1 received equine pituitary extract (EPE) on Day 5 after ovulation, Group 2 got the EPE on Day 12, while Group 3 had a combination of a 3.3 mg GnRH analogue (buserelin implant) on the day of ovulation, and EPE on Day 12.
• All groups were administered with 10 mg PGF2alpha on the first and second day of EPE treatment, intended to contract the uterus and regress the corpus luteum.

Procedure and Results

• The EPE treatment was continued daily till the first spontaneous ovulation. When that happened, each mare was given a dose of 3,300 IU of human chorionic gonadotropin (hCG) to induce further ovulations.
• Any mare in estrus with a follicle of 35 mm or larger was inseminated every two days with pooled semen from two stallions. The researchers then attempted to recover embryos seven days after their last ovulation.
• The researchers used follicular changes and embryo recovery during 15 estrous cycles prior to treatment as control data.
• It was observed that there was a significantly higher number of follicles of size 25 mm or larger in mares treated with EPE on day 5 compared to those treated on day 12 or control mares. However, this number was similar to mares that got the buserelin implants (Group 3).

Findings and Conclusion

• Initiation of the EPE treatment on Day 5 resulted in a more significant number of ovulations (2.9) than on Day 12 (1.1) or in the control mares (1.3).
• However, the number of embryos recovered was similar across all groups – Day 5 (1.2), Day 12 (1.0), buserelin (0.9) and control (0.9) groups.
• Two conclusions were drawn: Firstly, superovulation initiated early in diestrus using EPE leads to increased follicular development and ovulation. Secondly, the use of a GnRH analogue moderately enhances the response to EPE treatment.