The aim of thisexperiment was to compare the efficiency of a hormonal protocol, associatedto the temporary weaning for 96 hours, with the definitive weaning at 60 daysin beef cows, for the induction of estrus and ovulation. One hundred and eighty-threesuckled beef cows were used. The breeds of the cows were Charolais (C) and Nellore(N) and their crosses. The animals were genotyped as homozygous (HOM) and heterozigous(HET) for the microsatellite BMS3004, that is localized in the same chromossomeof the LH b chain gene. The cows were distributedin two groups between 60 and 80 days postpartum (day 0). In the hormonal inductiongroup (HI), the cows (n=87) received (day 0) 250 mg of medroxiprogesteron acetatefor 8 days, 2.5 mg of estradiol benzoate (day 1) and 500 UI of eCG (day 7).On day 8, the calves were weaned for 96 hours. In the same day (day 8), thecows (n=96) of the other group were just submitted to early weaning (group EW).Twelve hours after weaning, artificial insemination (AI) was done during fourdays. After this period, they were mated. The first diagnosis of pregnancy (DP)was performed 60 days after the AI period and, the second, 60 days after theend of mating. The estrus rates were higher in cows from HI group than in thoseof EW group. In the HI group, the cows with body condition 2.5 and 3.0 presentedlower pregnancy rates at the 1st DP (29.6 and 46.4%) than in theEW group (56.0 and 72.2%). The rates of pregnancy in cows with body index 65-73did not differ between the HI and EW groups. The N cows of HI group presentedlower pregnancy rate at 1st DP than the F1 (27.7 vs. 64.2%), butwas not different than the C cows (40.0%). In the HI group, the pregnancy rateat the 2nd DP was lower in HOM cows than in the HET ones. The cowsin the early definitive weaning group showed to be more efficient than in thehormonal induction group to improve the pregnancy rate.
