Morphology and enzyme activities of the small intestine are modulated by dietary protein source in the preruminant calf

A study was undertaken to assess the impact of the protein nature and soya antigenicity on the morphology and some enzyme activities of the jejunum in preruminant calves. Twenty Holstein calves fitted with a duodenal cannula were fed a liquid diet based on skimmed milk powder (SMP) for 2 weeks. They were then switched onto diets containing a mixture of SMP and either antig enic heated soybean flour (HSF; n = 12) or hypo-antigenic soya protein conc entrate (SPC; n = 8) for 8 weeks, after which they were reverted back to th e SMP diet for 2 weeks. The diets contained similar amounts of digestible n itrogen and energy, and were fed at a rate of 55 g DM/kg(0.75)/d. Proximal jejunal biopsies were collected just before (week 0), during (weeks 2 and 8 ) and after (week 10) feeding of the soya-based diets, and were used for mo rphology measurements and the determination of total alkaline phosphatase, lactase, amino-peptidases A and N, and dipeptidyl peptidase N activities. F eed intake and growth were similar between the HSF and SPC groups during th e experimental period. The effects of antigenicity and the antigenicity x t ime interaction were never significant (P > 0.05). Villus height decreased (P < 0.01) between weeks 0 and 2, and increased (P < 0.05) between weeks 8 and 10. Villus width increased between weeks 2 and 8 (P < 0.001). Crypt dep th also increased between weeks 0 and 2 (P < 0.001). Specific activities of alkaline phosphatase (P < 0.01) and amino-peptidase N (P < 0.05) decreased between weeks 0 and 2. Conversely, those of alkaline phosphatase (P < 0.00 01), lactase (P < 0.01) and dipeptidyl-peptidase IV (P < 0.0001) increased between weeks 8 and 10. Specific activities for lactase and amino-peptidase N decreased (P < 0.01) between weeks 2 and 8. The treatments had little ef fects on the amino-peptidase A activity. In conclusion, the present work de monstrated that soybean protein markedly depressed the morphology and most enzyme activities of the calf small intestine. On the contrary, the in vitr o antigenicity of soybean protein had little influence on these parameters in this study. (C) Inra/Elsevier, Paris.