[Food conversion in the digestive system of juvenile bulls. 1. Conversion of protein and amino acids].

Fistulated bulls (duodenal bridge fistulas) received 10 rations containing 60% concentrate and combinations of carbohydrates from various sources to investigate the protein and amino acid flux in the digestive tract. With a constant crude protein concentration of 12-13% in the rations (adjusted by adding urea), an average of 85 +/- 8% of the crude protein ingested with the feed were found in the duodenum. The highest values were measured for rations containing wheat/dried sugar beet chips (97% and 67% resp.). The mean percentage of bacterial crude protein in the corrected total protein found in the duodenum was 69 +/- 11%. This fraction accounted for 53% and 51% respectively for the rations containing maize or fodder beet and increased to above 70% with the rations containing dried sugar beet chips. The amounts of lysine, threonine, methionine and glycine found in the duodenum were always higher than in the feed. The highest synthesis rates were found in animals receiving rations containing fodder beet or dried sugar beet chips, and the lowest was measured for dried sugar beet pulp. Glutamic acid was slight, and no histidine synthesis was detected. The concentration of the amino acids per kg dry matter digesta was similar for the individual amino acids. Crude bacterial protein productions was relatively low (80 to 113 g bacterial crude protein per kg digestible organic matter), but correlated with ration composition.