Recent updates on amino acid requirements of pigs based on phenotypic improvements: invited review

Amino acid (AA) requirements reported in previous literature, such as those of the National Research Council (NRC) published in 2012 based on pre-2010 data, do may not adequately reflect the improved genetic potential of pigs and thus require updating. Accordingly, this review aimed to provide recent updates on the AA requirements of pigs based on the standardized ileal digestible (SID) lysine (Lys) to net energy (NE) ratio (SID Lys:NE) and the ideal ratios of SID methionine (Met), threonine (Thr), tryptophan (Trp), valine (Val), and isoleucine (Ile) to SID Lys (SID AA:Lys), derived from meta-analyses for average daily gain (ADG) and gain-to-feed ratio. The optimal SID Lys:NE for ADG in this review are consistently greater than the ratios reported by the NRC across different phases, indicating that the improved genetic potential for lean growth requires greater optimal SID Lys:NE. The optimal SID Met:Lys, SID Trp:Lys, and SID Ile:Lys for ADG remain constant with increasing body weight (BW) of pigs, but the ratios are also greater than those reported by the NRC. However, the optimal SID Thr:Lys for ADG increases as BW of pigs increases, likely due to the increasing proportion of maintenance requirement relative to the total Thr requirement. The optimal SID Val:Lys for ADG is greater in the nursery phase than in the grower phases, suggesting that weaning-associated intestinal and immune challenges would increase requirement for Val. Both optimal SID Thr:Lys and SID Val:Lys are greater than the ratios reported by the NRC. In conclusion, these results suggest that the optimal SID Lys:NE and SID AA:Lys in pig diets are greater than the ratios reported by the NRC, and different ratios of SID Thr:Lys and SID Val:Lys should be applied for pigs with different BW.