The experiment evaluated the performance of Charolais (C) and Nellore (N) cows of three age classes, young (3 and 4 years), adult (5 to 7 years) and old (8 or more years), weaned at three (early weaning) or seven months in the fall (traditional weaning). The weight of the cows at the fall was 45 kg higher for the cows weaned at three months (T3) than for the cows weaned at seven months (T7). The body condition at seven months was also better for T3 cows (3.3 vs. 2.1 points). The T3 cows had higher weight gain from calving to the end of the reproductive period and showed higher percentage of estrus (81 vs. 51%), of pregnancy (67.2 vs. 37.3%) and shorter interval between calving and first estrus (102 vs. 114 days) than T7 cows. Adult cows displayed better body condition at seven months and showed higher reproductive performance than young and old cows. The difference in pregnancy rate between T3 and T7 was more evident in young cows (42.11 vs. 12.5%) and old cows (51.72 vs. 35.71%) than in adult cows (62.5 vs. 53.33%). The C cows were heavier then N cows, at calving, at three and seven months, and displayed better body condition at seven months. The effect of early weaning on reproductive performance was more evident for C cows. The pregnancy rate of C cows was 80.6% for the T3 and 41.9% for the T7, while for the N cows the percentages were 45.5 and 30.0%, respectively, for T3 and T7. For C cows, milk production and the calves (presence and suckling) showed a stronger suppression on reproduction, than for N cows.
Bos indicus; Bos taurus; estrus; early weaning; reproduction
