The aim of this experiment was to compare the efficiency of a hormonal protocol, associated to the temporary weaning for 96 hours, with the definitive weaning at 60 days in beef cows, for the induction of estrus and ovulation. One hundred and eighty-three suckled 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 chromossome of the LH beta chain gene. The cows were distributed in two groups between 60 and 80 days postpartum (day 0). In the hormonal induction group (HI), the cows (n=87) received (day 0) 250 mg of medroxiprogesteron acetate for 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), the cows (n=96) of the other group were just submitted to early weaning (group EW). Twelve hours after weaning, artificial insemination (AI) was done during four days. 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 the end of mating. The estrus rates were higher in cows from HI group than in those of EW group. In the HI group, the cows with body condition 2.5 and 3.0 presented lower pregnancy rates at the 1st DP (29.6 and 46.4%) than in the EW group (56.0 and 72.2%). The rates of pregnancy in cows with body index 65-73 did not differ between the HI and EW groups. The N cows of HI group presented lower pregnancy rate at 1st DP than the F1 (27.7 vs. 64.2%), but was not different than the C cows (40.0%). In the HI group, the pregnancy rate at the 2nd DP was lower in HOM cows than in the HET ones. The cows in the early definitive weaning group showed to be more efficient than in the hormonal induction group to improve the pregnancy rate.
hormonal induction; postpartum; body condition; body index; molecular marker; polimorphism of DNA
