A new approach for estrus induction in Arabian mares suffering from ovarian inactivity

Abstract

Twenty-six Arabian mares affected with ovarian inactivity, as monitored by the clinical examination and ultrasonographical scanning, were selected during December and January. These animals were subjected to a new protocol of sequential hormonal injections as a trial for estrus induction, progesterone (300 mg/day) was injected on days 1,4,7,10 and 14, Estradiol benzoate (15mg/day) on days 6 and 9, and GnRH (0.01mg/day) on days 18, 20, and 22 of the treatment regimen. Anestrus induction response of 80.77% (21/26) was observed following hormonal treatment. The onset time of post-treatment was short (66.48 hours) and more synchronized. The responded group showed significant (P<0.05) increase in follicular size from the day -3 (3.26 cm) until reaching its maximum size at the pre-ovulatory day (4.48cm). This was accompanied by continuous significant (P<0.05)decrease in the serum concentrations of progesterone and increase in the levels of serum estradiol-17β from the day -3 (0.42 ng/ml and 56.48 pg/ml, respectively). The minimum level of progesterone (0.28 ng/ml) was detected at day 0 of ovulation, whereas the maximum level of estradiol-17β was observed at the preovulatory day (89.22 pg/ml). However, 28.57% (6/21) of the responded mares did not develop functional corpus luteum so confirmed by functional progesterone estimation. Reasons for failure of 19.23% mares (5/26) to respond to hormonal treatment could be due to the small size of emerging follicles at the end of treatment (1.05 vs 1.82 cm ) as well as the older ages of these animals (15.36 vs 8.87 years old) compared to the responded group.