MELENGESTROL ACETATE AND ESTRADIOL-17-BETA FOR SYNCHRONIZING ESTRUS AND IMPROVING REPRODUCTIVE-PERFORMANCE IN BEEF-CATTLE

Four experiments were conducted to investigate the use of melengestero l acetate (MGA) and estradiol-17 beta (E-17 beta) for synchronizing es trus and improving reproductive performance in beef cattle. Synchroniz ed pregnancy rates were higher (P < 0.05) in heifers fed MGA after AI than controls (4 of 9 versus 0 of 7, respectively), but were not diffe rent for cows (20 of 37, 54% versus 23 of 40, 58%). Estrus rate (perce ntage of cows detected in estrus) was higher (P < 0.05) for cows treat ed with E-17 beta + MGA compared with those treated with cloprostenol alone (85.0 versus 65.9%). Synchronized pregnancy rates were not signi ficantly affected by feeding MCA or grain only after detected estrus a nd Al (20 of 31, 64% versus 17 of 30, 57%). For 20 cows not detected i n estrus and bred 100 h after cloprostenol treatment, pregnancy rate w as higher (P < 0.05) for those fed MGA after AI than controls (6 of 11 , 54% versus 1 of 9, 11%). Feeding MGA after breeding may help to impr ove pregnancy rates.