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Abstract

The present study aimed to evaluate the Ovsynch program in Arabian mares compared to ovulation synchronization using progesterone. Twenty cyclic Arabian mares, averaging 5.9 years of age, were assigned for this study. Mares were randomly divided into two groups. The first group (GPG, n=10) received an IM injection of 40µg GnRH agonist at the beginning of the protocol and 250µg PGF2? analog on Day 7. Mares in this group were further assigned into two subgroups, G-PG-G(D9) (n=5, second GnRH agonist by Day 9) and G-PG-G(D12) (n=5, second GnRH by Day 12). The second group (G-P-PG-H(D19), n=10) was treated with oral progesterone for 14 days, 250µg PGF2? analog on Day 9, and 2500 hCG on Day 19. All animals were subjected to daily ultrasonographic examination. All animals were inseminated 24 hrs after the second GnRH (GPG) and hCG [G-P-PG-H(D19)] injections. Mares were bled at specific landmarks of the experiment, and sera were collected for progesterone and estradiol-17? assay. Compared to G-P-PG-H(D19)-treated mares, GPG group mares had longer estrus duration, larger DF, longer GnRH-ovulation, and longer AI-ovulation intervals. The conception rate was significantly lower (10%) for GPG compared to the G-P-PG-H(D19) (50%) groups. It can be concluded that factors like unreadiness of a considerable number of predestined ovulatory follicles for ovulation at the time of second GnRH administration, inordinate ovulation in response to second GnRH, and the long interval between insemination and ovulation are probably the reasons behind the low efficiency of this protocol in the Arabian mares.