DIGESTIBILITY, BLOOD-LEVELS OF NUTRIENTS AND SKIN-RESPONSES OF CALVESFED SOYBEAN AND LUPIN PROTEINS

Three milk substitute diets in which the protein was provided either b y skim milk only (control diet) or mainly (71%) by a commercial soyabe an or lupin concentrate (soyabean or lupin diet, respectively) were gi ven to intact or ileo-caecal-cannulated preruminant calves. In vitro t ests showed that both concentrates were partially proteolysed and had low antigenic and antitryptic activities. The low antigenicity was con firmed in vivo since none of the calves produced specific plasma antib odies against dietary proteins, and skin reactions following the injec tion of these proteins were minor. Post-prandial plasma level of trigl ycerides was higher with the 2 legume diets, suggesting faster abomasa l emptying of fat and probably protein. Apparent faecal nitrogen diges tibility was lower (P less than or equal to 0.05) with the soyabean an d lupin diets than with the control diet (0.86, 0.88 and 0.95, respect ively). At the ileal level, the differences were smaller and non-signi ficant (0.90, 0.88 and 0.92) for nitrogen, but remained significant fo r valine and tyrosine with the soyabean diet, and for proline, valine, methionine, leucine and lysine with the lupin diet. However, the diff erences were small enough to conclude that proper denaturation of soya bean and lupin proteins by processes including partial hydrolysis can suppress their antigenicity and render them very digestible.