Abstract
Eighteen Holstein-Friesian and 17 Japanease Black cows and heifers in anestrus with a palpable corpus luteum were injected intramuscularly with 25 mg of prostaglandin F2α (Tromethamine dinoprost). The luteolytic effect of the treatment was monitored by estimating progesterone levels in serum or skim milk before (day 0) and 3 days after the treatment.
Progesterone level (PL) showed four patterns of response. Type I: PL decreased from a base line of 1.0 ng/ml or higher to a value below 1.0 ng/ml 3 days after injection (17 cows). Type II: PL decreased from a base line of 2.0 ng/ml or higher to a value below 2.0 ng/ml, but not below 1.0 ng/ml (4 cows). Type III: PL did not decrease significantly, but remained at 1.0 ng/ml or higher (8 cows). Type IV: PL remained at a level below 1.0 ng/ml (6 cows). Cows which came into estrus within 6 days after the treatment and conception rate at induced estrus were 94%(l6/17) and 73%(8/11), respectively, in the Type I group, 100%(4/4) and 100%(4/4) in the Type II group, 50%(4/8) and 33%(1/3) in the Type III group, and 67%(4/6) and 33%(1/3) in the Type IV group.
Thus, PL was closely related to the appearance of estrus after the treatment and conception rate.
