Effect of dietary crude protein level on villous morphology, immune status and histochemistry parameters of digestive tract in weaning piglets

Fifty-five newborn, male piglets, was employed to investigate the effects of dietary crude protein level (CP) on the development of the digestive organs in piglets. Villous morphology, immune status, mucosa enzyme activity and glycogen, and DNA and RNA content of the digestive organs were determined, especially of the small intestine. Piglets were randomly allotted to five treatments and fed five diets containing CP 63, 103, 151, 208, or 249 g kg−1 diet (CP63, CP103, CP151, CP208, CP249), respectively. All piglets were given creep feed at day 7 and weaned at day 21. At the end of the experiment (42 days), six piglets of each treatment were slaughtered to collect tissue samples (duodenum, proximal jejunum, distal jejunum, ileum, stomach, pancreas and liver) for morphological and histochemical analyses. The results showed that dietary CP significantly affected villous height, crypt depth, intraepithelial lymphocytes (IELs), epithelial cell size, alkaline phosphatase (AKP), acid phosphatase (ADP), glycogen content, DNA and RNA density of some small intestinal sectors polynomially (P<0.05). In conclusion, there were linear or quadratic increases in the villous morphology and glycogen content of proximal and distal jejunum and linear decreases in the epithelial cell size along small intestine (besides ileum) as dietary CP increased from 63 to 249 g kg−1 diet. DNA density, RNA density and its differentiation in the small intestine also increased linearly or quadratically as the diet changed from CP63 to CP249.