Interaction between amino acids on the performances of individually housed piglets

Dietary branched-chain amino acid and tryptophan concentrations have been associated with effects on daily feed intake; this study is an extension of that research. We evaluated eight dietary treatments in a Latin square cross-over design with 32 female piglets during 8 weeks (9.9 ± 0.6 kg to 44.9 ± 2.9 kg, mean ± SD). Treatments differed in dietary standardized ileal digestible leucine (10.8 and 21.3 g/kg), valine (7.0 and 7.8 g/kg), isoleucine (6.0 or 7.3 g/kg) and tryptophan (2.0 and 2.5 g/kg) content. A longitudinal model was fitted with the level of valine, leucine, isoleucine, tryptophan and the interactions leucine × tryptophan, valine × leucine, isoleucine × tryptophan as fixed effects. Increasing the dietary leucine content decreased feed intake (-169 g/day) and daily gain (-168 g/day) of the pigs and impaired the feed conversion ratio (+0.49 g/g) (p < 0.01 for all parameters). Adding valine to the high leucine diet counteracted the feed intake reduction partially, while effects on daily gain and feed conversion ratio were largely counteracted by adding extra valine. The positive effect on feed conversion ratio diminished over time (p = 0.001 for age × valine). Adding extra tryptophan to the high leucine diet tended to negatively affect daily gain (p = 0.081) and feed conversion ratio (p = 0.074). Adding extra dietary isoleucine together with extra valine did not further counteract the negative effects of excess dietary leucine. The present results confirmed that, with excess leucine, extra valine benefits performance. Further adding extra tryptophan or isoleucine did not improve performances.