Practical Application of Ideal Protein Concept after 25 Years

Perhaps the greatest advance in establishing amino acid requirements for domestic animals, in the past 25 years, has been the implementation of the ideal protein concept (Fuller et al., 1989; Chung and Baker, 1992). This concept has been widely applied in pigs, poultry and dairy cattle nutrition. Calculations account for differences in specific amino acid patterns that are required for various physiological processes (e.g. maintenance, growth, pregnancy, lactation). In pigs, the requirement for each amino acid is expressed as a ratio to the lysine, the first limiting amino acid in typical pig diets. This pattern of essential amino acids is referred to as ‘ideal protein’ as it would precisely meet the physiologic needs of the animal. Importantly, the ideal amino acid pattern required for maintenance (M) differs from that for growth (G). The best illustration of how amino acids patterns vary with changing proportions of M and G is with pregnancy, where the ideal pattern for early pregnancy (low G, tissue deposition) differs from that in late pregnancy (increasing proportion of tissue growth beyond M; mammary, fetal growth, blood volume) (Kim et al., 2009; NRC Swine, 2012). The ideal protein method provides the basis for being dynamic with relative differences in G: M, and in systematically estimating requirements for all amino acids, without empirically proving the requirement for each amino acid. Animal Scientists take for granted this major advance. In contrast, this is one of the most urgent gaps identified for late pregnant and lactating human mothers and pre-maturely weaned children (Odle et al., 2016). Landmark changes in practical amino acid nutrition were set in place by academic leaders (D. Baker, M. Fuller), but integration into practice was driven primarily by Industry leaders. (J. Usry, M. Johnston, D. Boyd, G. Allee). The landscape of practical amino acid nutrition completely changed by (1) defining the lysine requirement curve and (2) relating the most limiting amino acids to lysine. This moved practicing nutritionists away from defining the requirement for each amino acid individually; each under differing conditions. Usry and co-workers proved the academic and financial importance of empirical calibration, and the extent to which certain amino acids change (or do not change) with stage of growth. The ideal protein concept solidified the move from protein formulation and provided a sensible guide as to other essential amino acid needs for pigs with genetically different rates of protein deposition and response to dietary lysine.