DESENVOLVIMENTO E DESEMPENHO REPRODUTIVO DE NOVILHAS DE CORTE SUBMETIDAS A DIFERENTES IDADES DE DESMAME

Abstract

The objective of the experiment was to evaluate the growth until twenty-eight months of age and the reproductive performance during the first mating at twenty- five months of beef females from two breeding systems, straightbreds (Charolais – C and Nellore – N) and crossbreds (1/2 CN, ½ NC), submitted to two ages of weaning: T3 – weaning at three months; T7 – weaning at seven months. After the weaning management heifers were kept only on pasture. The data collected were weights taken at three, four, seven, twelve, eighteen, twenty-four and twenty-eight months of age, average daily weight gain (ADG) between the different ages, body conditions at twenty-four and twenty-eight months, pelvic area and pregnancy rate. No significant interaction was observed for, the variables studied, between age at weaning and breeding system. ADG was lower for T3 calves from three to seven months (296 vs 434 g) and higher from seven to twelve months (541 vs 417 g), afterward no significant difference was observed between the two treatments. The only significant difference for weight was at seven months, when T7 calves showed higher weight (144 vs 128 kg). Weights at twenty-four months were 333 and 331 kg, respectively, for T3 and T7. Crossbred females showed higher weight gain from three to eighteen months and were heavier at twelve (11.73%), eighteen (17.10%), twenty-four (14.89%) and twenty-eight months (19.03%). No significant differences, between weaning ages, were observed for body condition and pelvic area. Pregnancy rate was similar between T7 (66.7%) and T3 (63.0%). Crossbred females showed higher body condition at twenty-four (3.8 vs 3.3 points) and twenty-eight months (3.66 vs 3.07 points) had larger pelvic area (158.29 vs 166.28 cm2) and higher pregnancy rate (79.1 vs 38.7%) than the straightbreds. When nutrition conditions are adequate the weaning at three months does not affect the weight nor the reproductive performance of heifers during the first breeding season. KEY WORDS: Bos taurus, Bos indicus, Charolais, crossbreeding, growth, early weaning, Nellore, reproduction.