The tissue and dietary protein and amino acid requirements of pigs from 8.0 to 20.0 kg live weight

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Abstract
Forty-three entire males were used to determine the pig's tissue requirements for protein and amino acids from 8·0 to 20·0 kg, and provide information on the capacity of diets formulated with conventional ingredients to contain the same levels and balances of amino acids as ideal protein to supply these nutrients. Seven diets with similar digestible energy (15·9 MJ digestible energy (DE) per kg) and crude protein concentrations from 119 to 232 g/kg (8·7 to 17·3 g lysine per kg) were offered ad libitum between 8·0 and 200 kg live weight. The rate of protein deposition was determined by comparative slaughter. The composition of the protein deposited in the whole empty body was determined from amino acid analyses of pigs killed at 8·0 kg and from the two extreme dietary treatments at 20·0 kg. Growth performance and the rates at which protein and lysine were deposited in the empty body increased linearly with increasing dietary protein concentration up to 187 g/kg and remained relatively constant thereafter. The corresponding dietary protein and lysine intakes required to support maximal protein accretion were 178 g/day (11·7 g/MJ DE) and 13·0 g/day (0·84 g/MJ DE) respectively. Based on the maximal deposition rates for protein (91·8 g/day), and lysine (5·96 g/day) and endogenous protein loss (77middot;6 g/day) estimated from the linear component of the relationship determined between protein deposition and apparent digestible protein intake, the pig's tissue requirements for protein and lysine were only 99·4 g/day (6·5 g/MJ DE) and 6·46 g/day (0·43 g/MJ DE) respectively. This disparity between the pig's tissue protein and amino acid requirements and the dietary levels needed to support these was associated with the fact that the apparent digestibility and biological value of the dietary protein were 0·92 and 0·602 respectively. Apart from small differences in the lysine content of body protein and the methionine: lysine ratio, the average amino acid composition of pigs killed at 8·0 kg, and from the diet of highest protein concentration at 20 kg, was similar to that of ideal protein, indicating that the low utilizability of dietary protein for tissue growth and maintenance was probably associated with low amino acid digestibility and/or availability. The implications of the results with respect to expression of the growing pig's requirements for protein and amino acids are discussed.