Predicting efficiency of use of metabolizable energy to net energy for gain and maintenance of Nellore cattle.
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Twenty-six comparative slaughter studies were used (n = 752 animals) and coded within each experiment by gender (431 bulls, 204 steers, and 117 heifers) and breed (447 Nellore and 305 Bos indicus and Bos taurus crossbreds) to develop equations to predict the efficiency of use of ME to NE for growth (kg) and ME to NE for maintenance (km). The retained energy (RE) was regressed on ME intake (MEI) available for gain using orthogonal regression to obtain the kg within each experiment. The estimated kg was regressed on RE as protein (REp) according to the following equation: kg = a/(b + REp). Gender and breed effects were not tested because of limited number of experiments. The km was estimated as the intercept of the following equation: HP = 0 e((1 MEI)), in which HP is heat production, 0 and 1 are coefficients, and e is the natural logarithm. The ME for maintenance (MEm) was computed assuming MEI equals to HP at maintenance. The km was obtained using the stepwise procedure of a multiple regression including ADG, empty body gain (EBG), empty BW (EBW), EBW(0.75), kg, and energy content in the EBW. A random coefficient model, assuming a random variation for study effects, was used to test breed and gender effects to identify the best model to estimate km. The overall equation to predict kg was 0.327 (0.142)/[0.539 (0.317) + REp], with an R(2) of 0.963. The equation to predict km was 0.513 (0.024) + 0.173 (0.061) kg + a EBG, R(2) = 0.92, in which a = 0.100 (0.021) for B. indicus or a = 0.073 (0.021) for crossbreds. Our results indicated that B. indicus were more efficient to use ME for maintenance. We concluded that km can be predicted from kg and EBG and that B. indicus B. taurus crossbreds can affect km. Furthermore, kg can be predicted from REp and neither gender nor crossbreeding (B. indicus B. taurus) affected kg. Because our database consisted of Nellore and B. indicus and B. taurus crossbreds, it is necessary to further evaluate differences between B. taurus and B. indicus regarding the kg.