EFFECT OF MELENGESTROL ACETATE ON SYNCHRONIZATION OF ESTRUS, SUBSEQUENT FERTILITY AND MILK CONSTITUENTS OF LACTATING DAIRY COWS

The oral effectiveness of melengestrol acetate in estrus synchronization and its effect on milk yield and milk constituents was determined in 40 lactating dairy cows. Melengestrol acetate was fed at a rate of 1.0 mg/head/day for 14 consecutive days in 0.91 kg of a grain diet. It was observed that melengestrol acetate did not significantly affect milk yield, milk fat, solids-not-fat, or lactose level. Cows were not observed in standing estrus during the feeding period of melengestrol acetate. The occurrence of estrus after withdrawal was 93%. The mean interval from melengestrol acetate withdrawal to onset of the first and second post-treatment estrus was 4.9 and 21.9 days, respectively. The over-all conception rate (first and second service) for the control group was 53%, as compared to 60% for the melengestrol acetate group. Estrus synchronization in the hot summer months tends to have a slight adverse effect on the occurrence of post-melengestrol acetate estrus and on fertility, when compared to estrus synchronization during the cool seasons of the year. © 1969, American Dairy Science Association. All rights reserved.