Improved soybean protein sources for early-weaned pigs: II. Effects on ileal amino acid digestibility

Early-weaned gilts fitted with simple ileal T-cannulas were used to determine the effect of protein source on N and amino acid (AA) digestibility. The digestibilities of N and AA in 25- to 53-d-old pigs fed either dried skim milk (DSM), isolated soybean protein (ISP), soybean protein concentrate (SPC), or soybean meal (SBM) as the only protein source were determined. The pigs were fed semipurified diets formulated to contain 22% CP. Digestibility of N and overall essential amino acids (EAA) and nonessential amino acids (NEAA) both at the terminal ileum and over the total digestive tract of early-weaned pigs was greater (P < .01) by pigs fed the DSM, ISP, and SPC diets than by those fed the SBM diet. The ileal and total tract digestibilities for N and all AA except glutamic acid (P < .05) increased with increasing age of pigs. Digestibility both at the ileum and total digestive tract for lysine was greater (P < .01) in pigs fed the DSM diet than in those fed any of the soybean protein diets. Digestibility values over the total tract were greater than values estimated at the ileum, indicating a net disappearance of both N and AA in the hindgut. This study suggests that low digestibility of the first-limiting AA, lysine, may limit performance of pigs fed a SBM diet.