Evaluation of alternative models of digestible lysine requirements from 3 models applied to 2 genetic populations of pigs with different body compositions

The objectives of this study were 1) to compare 3 models that predict daily lysine requirements and 2) to evaluate whether the relative differences in predicted lysine requirements for each model are similar for barrows and gilts within each of 2 genetic populations of pigs, high-lean and low-lean gain. Two models, Schinckel et al., 2003b (SCH-03) and NRC, 1998 (NRC-98), use constant estimates of the efficiency in which lysine is used for protein deposition. The NRC, 2012 (NRC-12), model uses efficiency values that decrease with increased BW. In addition, the NRC-12 model estimates greater digestible lysine is required for maintenance than the other 2 models. The 3 models predicted that high-lean-gain pigs had greater (25.5 to 27.3%) overall predicted lysine:NE ratios than did low-lean-gain pigs. The greatest differences between the models in their predicted total lysine requirements were after 75 kg of BW. At 75 kg of BW, the NRC-12 model predicted digestible lysine requirements of 15.64 g/d for all 4 genetic groups versus 14.67 and 13.40 g/d for the NRC-98 and SCH-03 models. The differences increased at 100 kg (17.17 vs. 15.43 and 14.11 g/d) and 125 kg of BW (18.69 vs. 16.16 and 14.78 g/d). The NRC-12 model predicted 6.5 and 16.7% greater total SID lysine was required from 25 to 125 kg of BW than the NRC-98 and SCH-03 models, respectively. The 3 models predicted similar differences in lysine requirements for the 4 groups of pigs. The NRC-12 model predicted greater daily lysine requirements than the previous models after 75 kg of BW.