Quantitative Efficacy of Dietary Isoleucine and Valine for Chick Growth as Influenced by Variable Quantities of Excess Dietary Leucine

Six assays were conducted with young chicks fed a crystalline amino acid diet to ascertain the effect of excess dietary leucine on valine and isoleucine efficacy (capacity of valine and isoleucine to promote chick weight gains). Valine efficacy appeared to decrease curvilinearly with increasing levels of dietary leucine. Based upon a fitted quadratic regression equation, valine efficacy reached a minimum value of 74% of normal at 5.57% excess dietary leucine. In contrast to valine, pooled results from three assays involving isoleucine deficiency indicated that isoleucine efficacy decreased linearly to about 80% of normal when 3% excess dietary leucine was fed.