Predicting net energy and protein requirements for growth of implanted and nonimplanted heifers and steers and nonimplanted bulls varying in body size

Energy and protein retained in 50, 38, and 54 nonimplanted Holstein and Angus heifers, steers, and bulls, respectively, 17 pens (237 cattle) of beef breed implanted heifers, and 65 pens (535 cattle) of beef breed implanted steers were compared to values predicted by the 1984 National Research Council (NRC), Cornell Net Carbohydrate and Protein System (CNCPS), and the model of Oltjen et al. (OLTJEN). The NRC accounted for 83, 85, 86, 88, and 88% of the variation in retained energy (RE) with biases of -8, +13, -6, +6, and -12% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. The CNCPS accounted for 93, 98, 92, 95, and 91% of the variation in RE with biases of +2, +10, -6, +1, and -13% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. OLTJEN accounted for 78, 76, 48, 93, and 96% of the variation with biases of -3, -2, +9, -8, and -1% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. For retained protein (RP), the NRC accounted for 57, 68, 70, 86, and 84% of the variation with biases of -12, -7, +16, -8, and -10% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. The CNCPS accounted for 69, 77, 84, 94, and 84% of the variation in RP with biases of -7, -11, 0, -3, and -9% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. OLTJEN accounted for 51, 38, 0, 35, and 69% of the variation with biases of -23, -2, -31, -4, and -38% for nonimplanted heifers, implanted heifers, nonimplanted steers, implanted steers, and bulls, respectively. This analysis indicates that the CNCPS, which uses a weight adjusted for body size and sex in the NRC 1984 medium-frame steer equation, can be used to predict both RE and RP for all classes of cattle (implanted and nonimplanted heifers, steers, and bulls varying in body size) when their weights are adjusted to that equivalent to the body size steer represented by that equation.