Standardised ileal digestibility of crystalline amino acids.

The basal ileal endogenous amino acid losses and the ileal digestibility of several crystalline amino acids have been determined in growing broilers. Lowest basal endogenous amino acid losses were found for Met and Trp and the highest for Thr. The ranking between the single amino acids within the basal endogenous losses was similar between the protein free diet assay of the present trial and the EHC assay reported in a recent literature survey. Ileal digestibility of the single crystalline amino acids including DL-Met, L-Lys, L-Thr, L-Thr and others were corrected (standardised) for basal endogenous losses. Standardised ileal digestibility of crystalline amino acids were consistently very close to 100 % regardless the methodology of standardisation. Data suggest a complete absorption of amino acids deriving from crystalline amino acids and thus an ileal digestibility figure of 100 % should be used in feed optimisation programs. Introduction The goal of feed production is to produce a feed matching the requirement for maximum broiler growth or breast meat yield, minimum feed conversion, or maximum profitability. In terms of amino acids, target levels can be achieved by an intelligent combination of various protein sources and supplemental amino acids like DL-Methionine, L-Lysine, L-Threonine, and L-Tryptophan. In future, potentially some more amino acids might be commercially available for feed production. However, the amino acids from intact proteins contributed to the diets by plant and/or animal by-product protein sources are not completely available for the bird. In contrast to that, amino acids from supplemental amino acid sources were often found to be 100 % digestible (Lewis et al., 1995). However, the research on this topic was exclusively based on the determination by the total tract or excreta amino acid digestibility assay. This approach has some methodological drawbacks which can be overcome by determination of ileal amino acid digestibility (Lemme et al., 2004). Thus, a trial was performed in order to determine the ileal digestibility of crystalline amino acids in growing broilers. Materials and Methods A total of 84 male ROSS 308 chicks were fed a commercial starter diet from day 1 to 16 of age. At day 17 (average body weight of 376 g) birds were housed in metabolism crates and distributed to 2 treatments with 6 replicates with 7 birds each. Experimental diets and water were offered ad libitum until day 22. The composition of the two experimental diets is given in Table 1. One was a protein or nitrogen free diet consisting mainly of starch but containing also oil, fiber, mineral and vitamin sources to avoid deficiencies. This diet was used to estimate the basal endogenous losses. In the second diet fed in order to determine the ileal digestibility of crystalline amino acids 9.1% of the starch of the nitrogen free diet was replaced by a mixture of crystalline amino acids as outlined in Table 2. Analyses of the diets verified a successful feed production. At day 22 all birds were slaughtered by cervical dislocation. The digesta from the terminal ileum (the part 40 cm to 5 cm anterior to the ileocecal junction) was quickly but gently collected, freeze-dried and stored until analysis for amino acids and Cr2O3 which was used as inert marker. Digestibility was then calculated according to the following formula: