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National audience; The effects of tryptophan (Trp) supplementation were investigated in growing pigs (n = 100 from 40 to 100 kg) fed ad libitum in a context of a reduction of the crude protein (CP) level. A control diet with a CP content close to the standard level (NP; 16.5%) was compared to four low CP diets (LP; 13.7%) gradually supplemented with L-Trp (0, 0.3, 0.6 and 0.9 g/kg for LP0, LP1, LP2 and LP3, respectively). All the diets were formulated to contain similar net energy (9.9 MJ/kg) and standardized ileal digestible (SID) lysine (Lys; 0.81%) contents. The actual SID Trp:Lys ratios were 22, 17, 20, 23 and 27% for NP, LP0, LP1, LP2, and LP3 diets, respectively. Growth performance decreased when pigs were fed a low CP diet without L-Trp supplementation (LP0 vs. NP, -160 g/d; P < 0.05). The average daily gain of pigs fed the LP1 diets was similar to that obtained with NP treatment (958 vs. 989 g/d; P > 0.05). Similar growth performances were measured in LP1, LP2 and LP3 groups. In our experimental conditions, the SID Trp:Lys ratio in growing pigs fed a low CP diet has to be at least 20% to optimize the growth performance.

De récentes études ont estimé les besoins en valine, isoleucine et leucine chez le porcelet. Bien que l’on puisse faire l’hypothèse que ces besoins peuvent être extrapolés aux porcs en phases de croissance et finition, cela n’a pas été confirmé expérimentalement. L’objectif est d’évaluer la réponse des porcs en croissance et finition à l’apport en valine, lysine et matières azotés totales (MAT) du régime. Des porcs alimentés à partir de 45 ou 90 kg de poids vif pendant 3 semaines avec trois régimes à teneurs différentes en valine, lysine et MAT. Un régime à bas taux protéique (régime A) a été formulé pour être limitant en valine [58% digestibilité iléal standardisé (DIS) valine:lysine] et sub‐limitant en lysine. Deux régimes ont couvert les besoins en valine (régime B) et en valine et lysine (régime C). Le régime D était similaire au régime C mais avec un haut niveau en MAT. Aux deux stades, la consommation et la croissance ont été réduites de 10‐15% chez les animaux qui recevaient le régime A en comparaison avec les autres. La meilleure performance a été observée chez les animaux qui recevaient les régimes B et C, sans différence entre eux. La consommation était ou tendait à être réduite chez les animaux recevant le régime D en comparaison avec les régimes B et C. En conclusion, la réduction de la MAT dans l’aliment n’a pas eu d’impact sur les performances des porcs en croissance et finition quand les besoins en acides aminés étaient couverts. Il apparaît également que la valine est potentiellement limitante dans l’alimentation de ces porcs., Recent studies have been carried out to determine the requirements for valine, isoleucine, and leucine in piglets. Although it is hypothesized that these requirements can be extrapolated to growing and finishing pigs, this has not been confirmed experimentally. The objective of this study was to test the response of growing and finishing pigs to the valine, lysine, and crude protein (CP) contents in the diet. Pigs with an initial body weight of 45 or 90 kg were fed for 3 weeks with diets differing in valine, lysine and CP contents. A low‐CP diet (diet A) was formulated to be limiting in valine [58% standardized ileal digestible (SID) valine:lysine] and sub‐limiting in lysine. Two other diets (based on diet A) were formulated to cover the valine requirement (diet B) and valine and lysine requirements (diet C). Diet D was similar to diet C but with a higher CP content. At both stages, feed intake and growth rate were 10‐15% lower in pigs receiving diet A compared to those receiving the other diets. The best performance was observed in pigs receiving diets B and C, with no difference between these treatments. Feed intake was or tended to be lower in pigs receiving diet D compared with those receiving diets B and C. In conclusion, a reduction in the dietary CP content had no impact on performance of growing and finishing pigs as long as the amino acid requirements were met, and valine can be a potentially limiting amino acid in the diet of these pigs.