Survival of dietary antigens in the digestive tract of calves intolerant to soybean products.

Preruminant calves were given a series of feeds containing heated soybean flour. Digesta collected from the small intestine were analysed by haemagglutination inhibition assay for soluble soybean antigens. The presence of undenatured glycinin and beta-conglycinin in ileal contents was associated with digestive disturbances. In vitro experiments showed that, under optimal conditions of pH for protease activity, beta-conglycinin but not glycinin, was unaffected by pepsin and both antigens were resistant to rennin and trypsin. The solubility of glycinin and beta-conglycinin in saline extracts remained high over pH ranges of 2 to 3 and 6 to 10 but under conditions of intermediate pH, about 4.5, solubility was minimal. It was concluded that preruminant calves suffer from gastrointestinal hypersensitive responses to certain soybean products because major proteases of the digestive tract fail to denature soluble antigenic constituents of the soybean protein.