Effect of Melengestrol Acetate on Synchronization of Estrus, Subsequent Fertility and Milk Constituents of Lactating Dairy Cows

Abstract

The oral effectiveness of melengestrol ace- tate in estrus synchronization and its effect on milk yield and milk constituents was determined in 40 lactating dairy cows. Me- lengestrol acetate was fed at a rate of ).0 mg/head/day for )4 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 con- trol 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 es- trus and on fertility, when compared to estrus synchronization during the cool sea- sons of the year.