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Is the broiler response to dietary valine modulated by the same branched-chain amino acids as in piglets

Zouaoui, M., W. Lambert, A. Simongiovanni and M. Létourneau-Montminy

Branched-chain amino acids (BCAA), that include valine (Val), leucine (Leu) and isoleucine (Ile), share the same unique catabolism pathway, leading to strong metabolic interactions. Excess of dietary Leu was first shown in piglets to stimulate the degradation of all BCAA including Val and Ile, with negative consequences on feed intake and growth. The aim of this study was thus to quantify and compare the response of broilers and piglets to dietary Val and the impact of the two others BCAA, Leu and Ile, on this response thanks to a meta-analysis approach. The databases were composed of 23 articles published between 1999 and 2018 including 44 experiments and 239 treatments for broilers, and 16 articles published between 2001 and 2018 including 23 experiments and 126 treatments for piglets. Multiple regression models were fitted with the MIXED procedure of Minitab software with experiment as random effect. The Y variables were average daily gain (ADG), average daily feed intake (ADFI) and feed conversion ratio (FCR). For broilers, the Y variables were expressed in percentage of the highest level intra- experiment to make the values comparable between experiments (different ages and genetic lines). The main X variable was the dietary standardised ileal digestible Val level (ValSID) and the other ones were dietary SID Leu and Ile (LeuSID and IleSID, respectively). The response of ADG and ADFI to ValSID was linear and quadratic for broilers and piglets (Broilers, ADG: P < 0.001, R2=0.65, ADFI: P < 0.001, R2=0.50; Piglets, ADG: P < 0.001, R2=0.93, ADFI: P < 0.001, R2=0.97). Results showed that increasing dietary LeuSID reduced ADG and ADFI in broilers and piglets (P < 0.05) but also that the response to ValSID was stronger with high LeuSID levels for these 2 species (Interaction ValSID×LeuSID: Broilers, ADG and ADFI: P < 0.001; Piglets, ADG and ADFI: P < 0.05). The response of ADG and ADFI to ValSID was not modified by IleSID. The FCR responded linearly (P < 0.001) and quadratically (P < 0.001) to ValSID, while LeuSID and IleSID have no effect on this response for both species. In conclusion, the current study showed that ADG and ADFI but not FCR response to ValSID is modulated by dietary LeuSID level.

These results indicate that Leu is the most important regulator of BCAA metabolism that works similarly in broilers and pigs. This quantification will facilitate the decision-making on amino acid formulation constraints and the implementation of low protein diets for these two species.