Biological efficiency of a Charolais herd of different body sizes.

With the development of the agricultural sector and the growth of the agriculture area, occurred reductions in pasture areas, requiring greater efficiency of the livestock sector for the activity to continue. In this way, the animal size must be considered, since it is related to the cost of production, the maturation rate, the reproductive efficiency and, more important, the economic efficiency of the production systems. This study aimed to evaluate the production, reproductive performance and productive efficiency of predominantly Charolais cows and their calves (Pure, % C, % N) according to their body size at calving. Sixty-three cow:calf pairs were used and classified into the groups Light (331.4±5.8), Moderate (385.9±5.3) and Heavy (424.3±6.2). The classes were formed with half standard deviation above or below the average weight of cows at calving. For each pair, the body weight was evaluated at calving, at weaning (63 days), at the beginning and at end of the reproductive period, and calves at nine months. Pregnancy rates were similar (P>0.05) between weight groups. The calves did not differ (P>0.05) in weight and body weight gain from calving until 210 days. The calves from Heavy cows had greater weight variations from 210 days to 270 days if compared to Light cows. The calf production rate (kg calf/cow kept in herds) did not differ. However, upon relating it to the weight of the cows at 210 days, Light cows were more productive (P0,05) entre os grupos de peso. Os bezerros não diferiram (P>0,05) em peso e variação de peso corporal do nascimento aos 210 dias, tendo os bezerros, filhos de vacas Pesadas, maiores variações de peso dos 210 dias aos 270 dias comparado aos de vacas Leves. O índice de produção de bezerro (kg de bezerro/vaca mantida) não diferiu, no entanto, ao relacionar este ao peso das vacas aos 210 dias, vacas Leves foram mais produtivas (P