Digestibility, blood levels of nutrients and skin responses of calves fed soyabean and lupin proteins.

Three milk substitute diets in which the protein was provided either by skim milk only (control diet) or mainly (71%) by a commercial soyabean or lupin concentrate (soyabean or lupin diet, respectively) were given to intact or ileo-caecal-cannulated preruminant calves. In vitro tests showed that both concentrates were partially proteolysed and had low antigenic and antitryptic activities. The low antigenicity was confirmed in vivo since none of the calves produced specific plasma antibodies against dietary proteins, and skin reactions following the injection of these proteins were minor. Postprandial plasma level of triglycerides was higher with the 2 legume diets, suggesting faster abomasal emptying of fat and probably protein. Apparent faecal nitrogen digestibility was lower (P < or = 0.05) with the soyabean and lupin diets than with the control diet (0.86, 0.88 and 0.95, respectively). At the ileal level, the differences were smaller and non-significant (0.90, 0.88 and 0.92) for nitrogen, but remained significant for valine and tyrosine with the soyabean diet, and for proline, valine, methionine, leucine and lysine with the lupin diet. However, the differences were small enough to conclude that proper denaturation of soyabean and lupin proteins by processes including partial hydrolysis can suppress their antigenicity and render them very digestible.

Hydrolyzed soy protein isolate sustains high nutritional performance in veal calves.

Milk replacers containing skim milk powder or a mixture of whey and soy protein provided by a hydrolyzed soy protein isolate or a heated soybean flour were fed to 1-mo-old calves for 101 d. The isolate and the flour provided 56 and 72% of dietary proteins, respectively. Digestibility of feed constituents was measured between 9 to 14 d and 65 to 70 d of treatment. Digestive function was evaluated by measurement of ruminal pH, plasma kinetics of triglyceride and glucose concentrations, and xylose absorption. Antibody production was also recorded. Growth and carcass characteristics were satisfactory for the control diet and the diet based on soy isolate, partly because of high apparent digestibility of protein and lack of antibody synthesis in response to soy isolate. In contrast, protein from soybean flour was poorly digested and highly immunogenic. Ruminal pH at 2.5 h after the meal was unaffected by dietary treatments. Postprandial changes in concentrations of triglycerides and glucose in plasma suggested a lack of abomasal clotting with both diets based on soy. Xylose concentration in plasma was only slightly affected by dietary treatment and calf age. Hydrolyzed soy protein is suitable for veal calves and can account for at least half of protein intake.