Influence of dietary level of dispensable amino acids on nitrogen balance and whole-body protein turnover in growing pigs

A nitrogen balance and a whole-body protein turnover experiment was carried our with 12 growing female crossbred pigs, 45 kg bodyweight (BW) to study the effect of increasing dietary levels of dispensable amino acids (DAA, 5% , 9% and 14%) at constant contents of indispensable amino acids (7%). Whole -body protein turnover was determined using the end-product method after a single oral dose of N-15-glycine to a semisynthetic diet. Daily N intake wa s 1.45, 1.96 and 2.48 g/kg BW75 for low, medium and high DAA levels. The di etary protein was absorbed completely irrespective of treatment. Raising di etary DAA increased urinary N excretion and N retention (urinary N, 0.16, 0 .44 and 0.80 g/kg BW0.75/day; N retention, 1.20, 1.42 and 1.58 g/kg BW75/da y). Whole-body protein synthesis and degradation varied from 4.31 to 7.44 g N/kg BW0.75/day and from 2.88 to 6.24 g N/kg BW0.75/day. The respective mi nimum values were observed at the medium DAA level. It appears that the cou pling of anabolic processes of protein metabolism was maximal at medium die tary DAA contents.