Exogenous hormone regimens to utilize successfully mares in dioestrus (days 2-14 after ovulation) as embryo transfer recipients.

This study explored the use of two hormone regimens to enhance successful embryonic transfers in horse mares with a specific focus on those in the post-ovulation period.

Objective and Methodology

• The research aimed at successfully using mares in the post-ovulation period (2-14 days) as recipients of embryo transfers.
• Two distinct hormone regimens were employed during the experiment to achieve this aim, tested across two separate experiments.

Experiment I

• The first experiment focused on 20 embryos transferred non-surgically into recipient mares that had been administered 22 mg of altrenogest daily from the day of the recipient mare’s ovulation.
• The results revealed higher pregnancy rates among mares that were 2-6 days after ovulation at the time of transfer compared to those that were 7-12 days after ovulation.

Experiment II

• The second experiment involved a more complex regimen involving several types of hormones administered at different times after the donor mare ovulated.
• The recipients mares received 10 mg PGF-2 alpha at 0 hours, 20 mg oestradiol cypionate at 12, 24, and 36 hours, 500 mg of progesterone in oil at 48 hours, and then 22 mg altrenogest at 60, 72, and 96 hours. The altrenogest administration was continued until Day 28.
• The pregnancy rate was notably higher for the 12 recipient mares which were 10-14 days after ovulation than for the 10 mares that were 5-8 days after ovulation when treatment began.
• Within this group, early embryonic loss was detected in half of the pregnant recipient mares between Days 21 and 28 of gestation.

Conclusion

• Based on the results from both experiments, the researchers suggested that mares which are 2-14 days post ovulation and not in ovulation synchrony with the donor could still be utilized as embryo transfer recipients.
• For those mares in the early post-ovulation period, altrenogest could be administered, while those in mid- to late post-ovulation period can be placed on the more complex hormone regimen.