A moderate threonine deficiency may affect differently tissue protein metabolism. In this study, we compared protein metabolism in the small and large intestines, the liver, and the carcass of piglets (Sus scrofa) pair-fed either a control well-balanced diet (C: 9.3 g threonine/kg diet) or a low threonine diet (LT: 6.5 g threonine/kg diet) for 2 weeks. In the small intestine, the LT diet did not modify protein deposition, fractional protein synthesis rate (K(S)) and AA protein composition. Ubiquitin mRNA level, a component of the ubiquitin-dependent proteolytic pathway, was significantly decreased in the jejunum of the LT piglets. Protein deposition measured in the carcass and the colon, and KS measured in the semitendinosus muscle and the colon, did not differ between LT and C piglets. Nevertheless, in these compartments, threonine content was reduced indicating deposition of proteins less rich in threonine. In the liver, protein retention was reduced, K(S) was increased and AA protein composition was modified in the LT compared to the C piglets. In conclusion compared to the other compartments, small intestinal protein metabolism seems to be less sensitive to a moderate dietary threonine deficiency. This indicates that dietary threonine extraction by the small intestine may reduce threonine availability for the other tissues when young piglets were fed a diet marginally deficient in threonine. (C) 2009 Elsevier Inc. All rights reserved.