The aim of this study was to investigate the impact of a protein-free diet or diets differing in protein level on the morphology and enzyme activities of the small intestinal mucosa of the pre-ruminant calf.

Diets contained 14, 104, 205 and 279 g crude protein (CP) per kg dry matter (DM) supplied by skimmed-milk powder (SMP) and cream. Holstein male calves (no. = 6) aged 6 weeks (65 to 75 kg) were fitted with an abomasal catheter and simple T-piece cannulae in the duodenum, jejunum and ileum. The milk replacers were continuously infused into the abomasum. Each calf tested the four diets randomly during four experimental periods. Biopsies of intestinal mucosa were collected at each intestinal site through the cannulae and were used for morphology measurements (villus and crypt area, height and width) and the determination of the activities of dipeptidyl-peptidase IV, amino-peptidases A and N, lactase and alkaline phosphatase.

When the dietary CP level increased from 14 to 205 g/kg DM, villus height quadratically increased by proportionately 0·35 (P < 0·05) and crypt width linearly increased by proportionately 0·25 (P < 0·01) at the jejunum. This effect was associated with linear increases in the activities of dipeptidyl-peptidase IV and lactase and a quadratic increase in the activity of alkaline phosphatase.

To conclude, feeding a protein-free diet impacted negatively on the morphology and hydrolytic activity of the calf’s small intestine. These observations may partly explain the fact that endogenous protein losses measured with such a diet are often lower than in physiological conditions.