Effect of prostaglandin F2αadministered before estrus synchronization with norgestomet and estradiol valerate on calving rates of beef cows

Three experiments were conducted to evaluate the effects of prostaglandin F2αtreatments 5, 9, and 14 d before Syncro-Mate B® on calving rates of 1,072 beef cows from inseminations at a pre-set time. The administration of prostaglandin F2α5 d before Syncro-Mate B decreased (P< .01) calving rates. This reduction was associated with lower (P< .05) calving rates in cows administered Syncro-Mate B in the first half of the estrous cycle. Calving rates were unaffected in cows administered prostaglandin F2α9 d before Syncro-Mate B. The administration of prostaglandin F2α14 d before Syncro-Mate B reduced (P< .05) calving rates in previously anestrous cows. In summary, prostaglandin F2αshould not be administered to postpartum cows 5 to 14 d before Syncro-Mate B synchronization.