The Energy Requirement for Maintenance of Nellore Crossbreds in Tropical Conditions during the Finishing Period

This study determined the energy requirement for maintenance of purebred Nellore cattle and its crossbreds using data from a comparative slaughter trial in which animals were raised under the same plane of nutrition from birth through slaughter and born from a single commercial Nellore cow herd. Seventy-nine castrated steers (361 ± 54 kg initial BW) were used in a completely randomized design by age (22 months ± 23 days of age) with four genetic groups (GG): Nellore (NL), ½ Angus x ½ Nellore (AN), ½ Canchim x ½ Nellore (CN), and ½ Simmental x ½ Nellore (SN). The experimental design provided ranges in ME intake, BW, and ADG needed to develop regression equations to predict NEm requirements. Four steers of each GG were slaughtered to determine the initial body composition. The remaining 63 steers were assigned to different nutritional treatments (NT) by GG; ad libitum or limit-fed treatments (receiving 70% of the daily feed of the ad libitum treatment of the same GG). Full BW was recorded at birth, weaning, 12, 18, and 22 months. In the feedlot, steers were fed for 101 days a diet containing (DM basis) 60% corn silage and 40% concentrate. No difference of age at weaning (P = 0.534) and slaughter (P = 0.179 and P = 0.896, for GG and NT, respectively) were observed. AN steers were heavier at weaning weight, yearling weight and had higher EBW (P = 0.007, P = 0.014 and P < 0.001, respectively) in comparison to NL, CN, and SN. There were no interactions (P > 0.05) between GG and NT for any variable evaluated. When fed ad libitum, AN steers had higher daily MEI (Mcal/d; P < 0.001) in comparison to NL, CN, and SN. On a constant age basis, differences were observed on body composition (P < 0.05) between GG. The slope (P = 0.600) and intercept (P = 0.702) of the regression of log HP on MEI were similar among GG. Evaluating at the same age and the same frame size, there were no differences in NEm requirement between Nellore and AN (P = 0.528), CN (P = 0.671), and SN (P = 0.706). The combined data indicated a NEm requirement of 86.8 kcal/d/kg 0.75 EBW and a MEm requirement had a common value of 137.53 kcal/d/kg 0.75 EBW. The km and kg values were similar among GG (P > 0.05 and P > 0.05, respectively) and were on average 63.2 and 26.0%, respectively. However, although not statistically different, the NEm values from NL showed a decrease in NEm of 5.76% compared to AN steers.