SPECIAL STORY FEED & ADDITIVE MAGAZINE September 2023 55 “Swine nutritionists in the US were the first to consider the impacts of leucine on animal performance as many finishing swine diets contain numerous synthetic amino acids to reduce crude protein and high levels of DDGS which is a high leucine ingredient. Researchers at Kansas State University conducted a thorough literature review and meta-analysis of published BCAA data and developed a predictive model which suggested that adjustments to valine and isoleucine ratios should be made based on the diets leucine level…” UNDERSTANDING THE ROLE OF DIETARY LEUCINE ON VALINE REQUIREMENT IN POULTRY DIETS Jason Lee Product Development Senior Manager at CJ BIO America PH.D. Poultry Science at Texas A&M University (USA) Historically, poultry production nutritionists focused on meeting minimum requirements in their diet formulations especially when focusing on amino acids. Typically, this would include lysine, methionine, total sulfur containing amino acids, threonine (Thr), valine (Val), arginine (Arg) and tryptophan (Trp). In recent years, the use of feed grade amino acids has increased in number and volume with the introduction and expanded use of first L-threonine and more recently with L-valine, L-arginine, and L-isoleucine. The expanded use of synthetic amino acids results in lower crude protein diets which has beneficial impacts on the environment, performance and welfare of the animal. As the crude protein level of the diet decreases, the actual nutrient value of the diet is closer to the minimum specification or requirement of the animal. Most nutritionists do not include a minimum requirement for the essential amino acid leucine, as it is typical in far excess of animal requirement, at least in US diets as many ingredients used in US diets contain elevated levels of leucine in relation to the other branched chain amino acids (BCAA), valine and isoleucine, especially in corn and corn products (Figure 1). Corn and DDGS have 2.5 times the amount of leucine as valine and 3.2 time the amount of leucine as isoleucine. Corn gluten meal has over 4 time the amount of leucine as valine and isoleucine. The importance of this relationship and distribution of BCAA in ingredients is due to the common metabolic pathways that BCAA share (Figure 2). All three BCAA share common enzymes in their catabolism to include BCAA aminotransferase (BCAT) and BCAA α-keto acid dehydrogenase (BCKD) complex. The BCAT reaction takes place in muscle and involves a reversible transfer of leucine, valine, and isoleucine to their corresponding branchedchain α-keto acids. The KIC, the α-keto acid of leucine, activates the BCKD complex (Harris et al., 2005), which increases an irreversible catabolism of both Val and Ile. Thus having excessive levels of dietary leucine can cause either a valine or isoleucine inadequacy when these are in the diet at the animal’s requirement which is more common in lower protein diets and diets that are utilizing L-threonine, L-valine, L-isoleucine, and/or L-arginine.
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