The objective of the experiment was to evaluate the biologic efficiency of Charolais (CH) and Nellore (NE) cows nursing CH and ½NE ½CH (produced by CH cows), NE and ½CH ½NE (produced by NE cows) calves, mantained together until weaning, on native pasture (NP) or winter (oat + italian rye grass) and summer (alexander grass) cultivated pasture (CP). Cows and calves were weighted at birth; 14; 42; 70; 98; 126; 154; 182 days; and at weaning. The cows milk yield was evaluated at the same date of the calves weighing, with exception at birth. When the animals were mantained on CP, higher efficiency of converting the quantity of litres (EFLIT) (7.7 vs 11 L/kg) and dry matter (DM) (EFMS) of milk (1.06 vs 1.47 kg DM/kg) produced by cow into kg of calf weight gain, was observed. Quadratic effect of postpartum period for EFLIT (y=18.222-.141DAY+.000463DAY²) and EFMS (y=2.341-.0182DAY+.000063DAY²) was verified. Linear reduction of the daily requeriment of total digestible nutrients (mantainance plus milk production) (NDT) (NDT/day) was observed, as the lactation period advanced, for cows mantained on CP (.004 kg) and NP (.007 kg). The total requeriment (calving to weaning) of NDT (NDT/total) was superior for cows mantained on CP (1093.1 vs 1014 kg). However, cows mantained on CP were more efficient for transformation of NDT/dia (7.9 vs 12.5) and NDT/total (5.8 vs 8.2) in calf weight gain. The quantity of kg of calf produced/100 kg of cow (EFKG) (.201 vs .159 kg/100kg/day) and kg of calf produced per unit of cow metabolic weight (UTM) (EFTM) (.009 vs .007 kg/UTM/day) were higher when the cows were mantained on CP. Cows nursing F1 calves required more NDT/day (5 vs 4.8 kg/day). However, were more efficient for EFKG (27.1 vs 23.5 kg/100 kg) and EFTM (1.21 vs 1.05 kg/UTM). For cows nursing crossbred calves, the EFKG was higher for CH (28.5 vs 25.6 kg/100 kg). When EFTM was considered, higher value was observed for CH (1.11 kg/UTM) than for NE (.99 kg/UTM) cows, when they nursed straigthbred calves.
Charolais; cow age; crossbred; heterosis; milk yield; Nellore
