Enzymes of the small intestine of the calf: effect of dietary protein source on the activities of some enzymes in the small intestinal mucosa and digesta

The objective of this study was to examine the effect of dietary protein source on the morphology and enzyme activities in the small intestinal mucosa and digesta of preruminant calves. The control diet contained skim milk powder. Plant proteins from soy concentrate (unhydrolysed or partially hydrolysed) and potato concentrate were incorporated into experimental diets. Duodenal, jejunal and ileal mucosal biopsies and digesta were collected from calves fitted with simple cannulae and continuously infused with milk replacers into the abomasum. Biopsies were used for morphology measurements. The activity of dipeptidylpeptidase IV, aminopeptidases, lactase and alkaline phosphatase was estimated in biopsies and digesta. Incorporating plant protein had a limited effect on the intestinal mucosa. A partial villus atrophy and crypt hyperplasia were noted with the soy concentrate only. Decreases in the activity of dipeptidylpeptidase IV with the potato concentrate diet and of aminopeptidase N and lactase with the hydrolysed soy concentrate diet, were also observed in ileal biopsies. Mucosal enzymes were released in the lumen and most of them accumulated in digesta of the distal small intestine. The activity of aminopeptidase N and lactase in ileal digesta was higher in calves fed the soy and potato concentrate diets than in those fed the control diet.