Abstract
The effects of $PGF2{\alpha}$ on the conception rate and the plasma levels of estradiol-$17{\beta}$ and progesterone of anestrus Cheju mares were investigated at the breeding and non-breeding seasons. The results obtained from this studies are as follows; 1. The durations of the estrus and diestrus after $PGF_2{\alpha}$ treatment persisted shorter than control cycle (p<0.05), but ovulation time was fast. 2. The levels of estradiol-$17{\beta}$ and progesteron before $PGF_2{\alpha}$ treatment showed 103.8pg/ml, 8.0ng/ml in breeding season and 72.8pg/ml, 4.7ng/ml in non-breeding season, respectively. 3. The levels of estradiol-$17{\beta}$ rose to 115.4~154.0pg/ml, and 90.8~27.0pg/ml from 2nd to 6th day after the treatment of $PGF_2{\alpha}$, in breeding and non-breeding seasons, respectively, while progesterone level dropped to 1ng/ml with the sign of estrus and at 8th day rose in breeding season (p<0.05). 4. Of thirty anestrus mares investigated for $PGF_2{\alpha}$ administration, 87.5% showed estrus on an average of 3.8 days after treatment and the conception rate was 62.5% in breeding season, but the estrus and conception rates dropped 40% and 20% in non-breeding season, respectively.