The requirement of valine for gilts in the initial phase is not influenced by moderate levels of leucine

ABSTRACT The objective of this study was to evaluate the standardized ileal digestible (SID) valine and SID leucine levels on performance, backfat thickness, longissimus dorsi depth, and biochemical blood parameters of starting gilts. A total of 72 gilts, with initial weight of 15.16±1.15 kg, were distributed in a randomized block design in a 2 × 4 factorial scheme, comprised of two SID leucine levels (1.20 and 1.77%) and four SID valine levels (0.58, 0.73, 0.88, and 1.03%), with nine replicates and one animal per experimental unit. No interactions were observed for growth performance parameters. Final weight and average daily gain presented linear and quadratic effects. Setting data to the quadratic model associated with the Linear Response Plateau model, the optimal level of SID valine for average daily gain was achieved at 0.703%. A quadratic effect was also observed for average daily feed intake (ADFI), estimating the highest ADFI at 0.822% of SID valine. No branched chain amino acid (BCAA) effects were observed for backfat thickness, longissimus dorsi depth, and lean meat percentage. The interaction between levels of BCAA showed that the highest SID leucine levels (1.77%) provided a high plasma urea concentration only at low SID valine levels (0.58 and 0.73%). The SID valine requirement of starting gilts for a maximum average daily gain is achieved at 0.703%, corresponding to 9.72 g day−1, and is not affected by SID leucine levels currently used in conventional diets.