Abstract
Prostaglandin F2α (PGF2α) and estradiol benzoate (E2B) were used for synchronization of estrus and the fertility at the first synchronized estrus after the treatment was investigated in the grazing cow.
A total of 31 cows (Holstein) in the functional luteal phase of the estrous cycle were alloted to two experimental groups; i, e. Group A (15 cows) received an intramuscular (i. m.) injection with 15 mg of PGF2α and Group B (16 cows) received the simultaneous i. m. injection with 15 mg of PGF2α and 0.5 mg of E2B. Cows in both groups were observed for standing estrus every 6 h during the period of 24 to 96 h after the treatment and were inseminated 10 to 24 h after being detected in estrus. The time of ovulation was examined every 6 to 12 h, and diagnosis of pregnancy was made between 46 and 48 days after the insemination by rectal palpation.
Number of cows showed estrus within 96 h after the treatment in Groups A and B were 13 cows (86.7%) and 15 cows (93.8%), respectively. However, estrus occurred in 13 cows (86.7%) during 3784 h of the post treatment period in Group A, and in 14 cows (87.5%) during 3160 h of the post treatment period in Group B. The average interval±S. D. from the treatment to estrus for the cows showing estrus within 96 h after the treatment in Groups A and B were 58.6±12.0 h and 45.6±14.0 h respectively. Ovulation occured in 10 cows (66.7%) during the period of 7396 h after the treatment in Group A, in 13 cows (81.3%) during the period of 6184 h after the treat-ment in Group B. The average interval±S. D. form the treatment to ovulation for the cows ovulated within 120 h after the treatment in Groups A and B were 89.6±11.8 h and 71.9±8.8 h, respectively. The corpora lutea which developed after the ovulation at the synchronized estrus were normal 1114 days after the inseintion in the most of cows in both groups, but those of 2 cows in Group B were detected small in size by rectal palpation. Conception rate by the insemination during 49120 h of the post treatment period was not different in both groups, 53.9% (7 of 13 cows) for Group A and 56.3% (9 of 16 cows) for group B. However, of 16 cows in Group B, 14 cows were inseminated during the period of 4972 h after the treatment and 9 cows (64.3%) conceived.
These results indicated that the interval from the treatment to estrus and ovulation could be reduced, and the occurrence of estrus and ovulation were synchronized precisely by the simultaneous i. m. injection of PGF2α and the lower dose of E2B, and E2αB had no adverse effect on conception rate. Further investigation in large number of cows are needed to be sure whether or not the simultaneous injection of E2B with PGF2α will result in normal conception rate.
