Research note: Comparison of apparent and standardized ileal digestibility of amino acids in corn-soybean meal-based diets for laying hens at different ages

This study aimed to assess and compare the apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of amino acids (AA) in laying hens at different ages. A total of 180 28-wk-old Hy-Line Brown laying hens were randomly assigned to 3 age groups of 30, 50, and 70 wks. At each designated age, 60 hens were randomly allotted to 2 treatment diets: nitrogen-free diet (NFD) for estimating basal endogenous losses (BEL) of AA and corn-soybean meal-based diet (CSD). It was observed that the BEL of most AA increased with age, with significant increases (P < 0.05) for Arg, Lys, Thr, Asp, and Ser by an average of 118.3 % for these 5 AA in 70-wk-old hens than in 30-wk-old hens. The AID and SID of most AA in CSD decreased as hens were aged, with 70-wk-old hens exhibiting significant reductions (P < 0.05) in the AID of Arg and Lys by an average of 10.4 %, and in the SID of these 2 AA by 7.6 % compared with 30-wk-old hens. The AID and SID of Met were also lower (P < 0.05) in 70-wk-old hens by an average of 12.5 % and 10.7 %, respectively, than in both 30-wk-old and 50-wk-old hens. In conclusion, the BEL of AA increased, whereas AA digestibility decreased with advancing age in laying hens. Specifically, 70-wk-old hens showed decreased digestibility of limiting AA (Arg, Lys, and Met) compared with younger hens. Therefore, age-dependent AA digestibility in laying hens should be considered to improve the precision of feed formulation.