Abstract:
The objectives of this study were to investigate the ovarian activity and changing of serum estradiol-17 beta (E[subscript 2]) for detection of first postpartum estrus. Thirty Thai crossbred native mares were used in the study. All mares were teased daily and their ovarian follicular changes were monitored using ultrasonography and rectal palpation every other day from day 5[superscript th] postpartum until the mare showed estrous signs,then,daily examined until the ovulation occurred. Whereas, the mares that failed to show an overt estrus were examined every other day until ovulation or until day 21[superscript st] postpartum. Blood samples were taken from all mares, at examination time, for radioimmunoassay E[subscript 2] analysis. The results of twenty-five mares showed that ovulation occurred within 20 days postpartum in 23 (92%) mares but only 10 (40%) mares showed first postpartum estrus. Interval of foaling to first estrus and to first ovulation from these mares were 10.30+-2.95 and 13.39+-2.61 days, respectively. The mares that showed postpartum estrus had a significant higher in the diameters of preovulatory follicles than those of the mares failed to show the first postpartum estrus (43.54+-6.67 vs 38.55+-2.38 mm., respectively; P<0.05). Serum E[subscript 2] increased from 7.01+-2.96 pg/ml. to a peak of 10.79+-3.3 pg/ml. 2 days before ovulation. The peak of E[subscript 2] in the mares, with postpartum estrus, was significantly higher than that in the mares without estrus signs (11.9+-3.72 vs 8.45+-2.28 pg/ml., respectively; P<0.05). A significant correlation were found between the size of largest follicle and the maximum concentration of serum E[subscript 2] in both groups (P<0.05). These results demonstrated that the postpartum breeding management by careful examination of ovarian activity with various method may be able to increase breeding performance and foal production