Uterine Involution, Ovarian Activity, and Fertility after Melengestrol Acetate and Estradiol in Early Postpartum Cows

Abstract

Twenty-seven Holstein cows were assigned to control, melengestrol acetate,22Melengestrol acetate was generously supplied by Dr. J. W. Lauderdale, The Upjohn Company, Kalamazoo, Michigan. or melengestrol acetate plus estradiol groups. Melengestrol acetate was fed 1 mg/cow per day for 14 days beginning 21 ±1 days after calving. Estradiol benzoate33Sigma Chemical Co. (500μg) was injected intramuscularly 48h after the last melengestrol acetate feeding. Cows were inseminated at first and any subsequent estrus after 50 days postpartum. Weekly palpation per rectum revealed diameter of the largest uterine horn decreased until 7 wk postpartum, but there was no significant difference among treatment groups. A temporary plateau in diameter of the largest uterine horn in cows treated with melengestrol acetate occurred the week after treatment. Cows receiving melengestrol acetate had more follicles>1.0cm diameter but only during treatment. There was no significant difference in interval to first ovulation or corpus luteum formation among the three groups. Control, melengestrol acetate, and melengestrol acetate plus estradiol group means for interval from calving to first estrus, days open for cows conceiving, and services per conception were 63±11, 37±9, and 41±7; 153±15, 83±6, and 101± 15; and 3.3±.8, 1.7±.3, and 2.1 ±.4. Values for the control group were higher than values for the other two groups. There was no difference in milk yield among the groups during the lactation in which melengestrol acetate was administered.