GnRH類似体投与により黄体化した卵胞嚢腫牛におけるPGF<SUB>2α</SUB>の発情誘起効果および受胎成績

Abstract

Seventy-five cows with ovarian follicular cysts were randomly assigned to two treatment groups, A and B. Group A of 31 cows was injected intramuscularly with both 100μg of GnRH analog (GnRH·A)(fertirelin) and 25 mg of PGF2α THAM salt at an interval of 10 to 14 days. Group B of 44 cows was given 100μg of GnRH·A and held under observation for the occurrence of normal estrus, except those cows considered to have not responded to GnRH·A and retreated with 200μg of GnRH·A 10 to 14 days after the previous treatment. Progesterone concentrations in defatted milk were determined by ETA, and used for differential diagnosis of follicular and luteal cysts, and monitoring the luteinization of follicular cyst after GnRH·A treatment and the regression of luteinized cysts following PGF2α treatment.Of 6 cows of Group A and 38 Group B cows of defined to have follicular cysts on the basis of milk progesterone levels, 20 cows (76.9%) and 18 cows (47.4%) respectively, responded to GnRH·A with luteinization. Progesterone level in defatted milk decreased to less than 1.0 ng/ml within 6 days after PGF2α injection in 20 (100 %) of the 20 cows of Group A and 16 (80 %) of them exhibited behavioral estrus. The Percentage of cows inseminated within 100 days after the first treatment was significantly higher (P<0.05) in Group A 95%, 19/20 than in Group B 44.4%, 8/18. Average intervals in days between the initial GnRH·A treatment and the first AI were 19±9 days in Group A and 39±26 days in Group B. The difference was statistically significant (P<0.05). The percentage of cows which conceived within 100 days after GnRH·A treatment and the average interval between treatment and conception were 65%(13/20) and 33±19 days respectively, in Group A, and 40%(6/15) and 44±26 days in Group B. These results indicate that treatment with PGF2α of cows with luteinized cysts following treatment with GnRH is effective enough to shorten an interval between treatment and conception.