Determination of secretory IgA secretion and its contribution to total endogenous amino acid losses in broiler chickens fed a nitrogen-free diet or diets containing either casein or purified amino acids.

Secretory IgA (sIgA) secretion and its contributions to total endogenous amino acid (AA) losses were determined in broiler chickens. In Experiment 1, dietary treatments consisted of a nitrogen-free diet or a diet that contained 10% casein; both diets were provided to birds ad libitum. In Experiment 2, broilers received a nitrogen-free diet or diets containing 2.5, 5.0, 7.5, and 10% casein ad libitum. An additional diet was fed that contained a purified AA mixture that provided the same AA as the 10% casein diet. Another set of birds also received the 10% casein diet except birds were pair-fed to match AA intake of birds receiving the purified AA diet. In Experiment 3, broilers received ad libitum access to a nitrogen-free diet. Purified diets containing 10% casein or a purified AA mixture were also fed; the 10% casein diet was pair-fed to match AA intake of birds consuming purified AA. In each experiment, diets were fed from 18 to 21 d-of-age and sIgA secretion was measured in 6 to 11 pens of 5 broiler chickens. In Experiment 1, ileal sIgA was greater (P < 0.05) for the casein treatment compared with the nitrogen-free treatment. In Experiment 2, there was a linear increase (P < 0.05) in ileal and biliary sIgA as casein increased. Further, birds fed the 10% casein diet (pair-fed) secreted more sIgA (P < 0.05) compared with birds consuming purified AA. Proportional contributions of sIgA to total endogenous AA losses ranged from 0.5 to 5.2%. In Experiment 3, ileal sIgA was the greatest (P < 0.05) in broilers fed casein and there was no difference (P > 0.05) in ileal sIgA between the nitrogen-free and purified AA treatment. In conclusion, sIgA was a contributor to endogenous AA losses. Further, the addition of casein but not purified AA to a protein-free diet increased sIgA secretion; therefore, the presence of intact protein from casein, not the provision of AA per se, caused the increased sIgA secretion.