Effect of age and genetic group on the development of calves weaned at 63 days until one year of age

The development of beef calves born of Charolais (CH), Nellore (N), and Charolais × Nellore crossbred cows with Charolais (CHP) and Nellore (NP) predominance, was evaluated from birth to 12 months of age. The cows were grouped into three age classes: primiparous, young and adult. The net energy requirements for maintenance and gain of the calves were also evaluated, as were the production and availability of energy in the milk of the evaluated cows. We used 93 pairs of contemporary cows and calves maintained in natural pasture. From birth to 21 days of age and from 21 to 42 days of age, the calves of adult cows presented the highest average daily weight gain (ADG), while the calves of young and primiparous cows had similar ADG. The highest net energy requirements for maintenance (NEm) and gain (NEg) were for crossbred and Charolais calves, the latter being similar to Nellore calves. The energy available in the milk of the adult cows was 33% higher than that of primiparous cows. The weight gain of calves was influenced by the age of the cow until weaning. The pre-weaning and post-weaning weights of calves were affected by the genetic group, and adult and young cows produced heavier calves in the pre-weaning period than primiparous cows.