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.

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A series of experiments on the use of soybean as a protein source in milk replacers for veal calves was undertaken to determine the relationships between the physicochemical and antinutritional properties and apparent digestibilities of nine soybean products. Soybean provided between 58 and 71% of dietary CP, and skim milk or whey powder provided the remainder. Soybean products were analyzed for CP, native protein, aggregated protein, carbohydrate-linked protein, peptides, antitryptic activity, and immunoreactivity of lectin, glycinin, alpha-conglycinin, and beta-conglycinin. The apparent digestibility of N calculated for soybean protein varied between 59 and 84%. Simple linear correlations were significant between apparent digestibility of soybean N and concentrations of native protein, antitryptic activity, glycinin, alpha-conglycinin, and beta-conglycinin. However, only variation in antitryptic activity, alpha-conglycinin, and beta-conglycinin contributed significantly to an explanation for the variation in apparent digestibility of soybean N in a multiple linear equation. Under our experimental conditions, beta-conglycinin was the best predictor of digestibility of soybean N. Antitryptic activity became the best predictor when soybean products had no detectable beta-conglycinin.

Summary ― Three milk substitute diets, in which the protein was either provided exclusively by skim milk powder or partially (52%) substituted by a native wheat gluten or a potato protein concentrate, were given to intact or ileo-caecal cannulated preruminant calves. The apparent faecal nitrogen digestibility was lower (P < 0.05) with the potato than with the gluten and control diets (0.90, 0.93 and 0.95, respectively). The same trend was observed at the ileal level (0.83, 0.87 and 0.91, respectively). Apparent digestibilities of most amino acids were lower with the potato than with the control diet (P< 0.05 for glutamic acid, proline, cystine, methionine, isoleucine, leucine, tyrosine and lysine). The same trend was observed with the gluten diet. Apparent digestibilities of glutamic acid and cystine were also lower (P < 0.05) with the potato than with the gluten diet. Protein fractions of Mr 43 000 and below 14 000 were detected immunochemically in ileal digesta corresponding to the potato diet, but no immunoreactivity was found in digesta with the gluten diet. However, the considerable enrichment of digesta in glutamic acid and proline with gluten indicates that dietary protein fractions rich in these 2 amino acids escaped digestion in the small intestine. With the potato diet, the undigested fractions contained high levels of aspartic acid, glutamic acid and cystine. (respectivement 0,83, 0,87 et 0,91). La digestibilité apparente de la plupart des acides aminés a été moins élevée avec l'aliment pomme de terre qu'avec l'aliment témoin (p < 0,05 pour l'acide glutamique, la proline, la cystine, la méthionine, l'isoleucine, la leucine, la tyrosine et la lysine). Il en a été de même pour l'aliment gluten, mais seule la différence concernant la lysine a été significative. La

Summary ― The intestinal permeability to markers was assessed in preruminant calves fed different milk substitutes containing skimmed milk powder or whey and soyabean products of differing antigenic activity as the protein sources. In Experiment 1, the 6 h urinary excretion of lactulose transiently decreased with the antigenic soyabean product but not that of sucrose or D -mannitol. In Experiment 2, the 6 h urinary excretion of sucrose and D -mannitol averaged 1-3%, regardless of age and dietary treatment. Cr-EDTA was recovered at rates of 2 and 4% after 6 and 24 h of urinary collection, respectively. The 24 h excretion of Cr-EDTA was lower in the calves fed the antigenic flour than in the controls after 2 weeks of experimental feeding (2.9 vs 6.0%, P < 0.05) but not thereafter. This transient decrease was also observed using D -xylose with the antigenic flour and with the non-antigenic concentrate (17 and 22% respectively vs 37%, P < 0.05). The