SPECIAL STORY FEED & ADDITIVE MAGAZINE September 2023 57 feed conversion and thus must be considered in all US broiler diets. INFLUENCE OF LEUCINE ON THE OTHER BCAA REQUIREMENTS As previously discussed, excess dietary leucine will increase the catabolism of valine and isoleucine and have a negative impact on animal performance if either or both of these amino acids are at or near the requirement. Cemin’s et al. (2019) model recommended consideration of and potential adjustment (increase) to valine, isoleucine, and tryptophan ratios based on the dietary leucine content. It is unclear currently, if tryptophan will/should be considered in any potential poultry model as tryptophan is typically present in most poultry diets at levels beyond genetic recommendations. Regardless, Maynard et al. (2021) data demonstrates that a valine and isoleucine ratio adjustment may be needed to avoid negative performance influences of high dietary leucine. Ospina-Rojas et al. (2017) reported that increasing levels of dig valine were required to optimize feed intake in broilers as dietary leucine increased (Figure 4) confirming that excess leucine stimulates the catabolism of valine. Interestingly, this concept/result is not a new idea nor is it unique to only broiler chickens. Jackson and Potter (1984) reported that increasing dietary leucine had significant stepwise negative effects on turkey poult body weight gain, however, the addition of added valine eliminated the reduction in body weight at all evaluated leucine levels (Figure 5). However, more recently as research has begun to focus on the relationship of dietary leucine on valine and isoleucine requirements, researchers have aimed to not only demonstrate the antagonism but to quantify the valine ratio adjustment necessary based on dietary leucine ratio. While conducting an experiment that included two titration curves in diets containing either 115% dLeu: dLys (low) or 145% dLeu: dLys (High), Figure 3. Response surface describing the relationship between feed conversion ratio of Cobb MV x 500 male broilers and diet digestible isoleucine, valine, and leucine levels relative to ileal digestible lysine. (Adopted from Maynard et al., 2021). Figure 5. Plot of leucine x valine interaction for 7-to-19-day turkey poult body weight gain (adopted from Jackson and Potter, 1984). Figure 4. Effects of leucine (Leu) levels on dietary optimal levels of Valine (Val) for feed intake in broilers fed lowprotein diets (Adapted from Ospina-Rojas et al., 2017).
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