Evaluating the Dietary Digestible Isoleucine to Digestible Lysine Ratio: A 28 to 42 Day-of-Age Broiler Study

Introduction Formulating diets according to the ideal protein concept allows for maximizing nitrogen utilization and minimizing nitrogen excretion [1]. One primary benefit of ideal protein is that once a ratio is established for a certain age, one can calculate the requirement of all other amino acids under a variety of conditions based on the digestible lysine (dLys) requirement [2]. Digestible Isoleucine (dIle) is one of the limiting essential amino acid for broilers. Previous research has dictated that in most practical diets, dIle and digestible Valine (dVal) are often limiting after digestible Threonine [3-4]. The optimum dIle:dLys ratio may impact the metabolic efficiency and growth performance of the bird, as well as the utilization of Val and other limiting amino acids. Several research reports have addressed the dIle needs of broilers throughout the growout period of broilers [5-10], although minimum recommendations for least-cost formulation vary. Baker et al. [3] recommended a dIle:dLys ratio of 61 for birds during the 14-21 day post-hatch phase. Research regarding the optimum dIle:dLys ratios beyond day 28, or close to slaughter, are sparse. Because of this, there is a need to further evaluate the importance of varying dIle:dLys upon processing measurements, particularly carcass and breast meat weights and yields.