Small intestinal morphology and bacterial populations in ileal digesta and feces of newly weaned pigs receiving a high dietary level of zinc oxide

A study was carried out to determine the effect of dietary supplementation of 3000 mg kg–¹ zinc oxide (ZnO) on the small intestinal morphology and populations of enterobacteriaceae, lactobacilli and clostridia in ileal digesta and feces of weaned pigs. At 17 d of age, 36 pigs from nine litters were fitted with simple T-cannulae at the distal ileum and after a 2-h post-surgery recovery returned to their sows. At 21 d of age, the pigs were weaned and housed in individual metabolism crates. Pigs were allocated to receive a standard starter diet supplemented with or without 3000 mg kg–¹ of ZnO. Ileal digesta and fecal samples were collected immediately before weaning and then on days 2, 4, 7, 9, and 11 after weaning and were used to quantify enterobacteriaceae, lactobacilli and clostridial populations by colony enumeration on selective media. Pigs were euthanized following the final sampling, and 2 cm sections of tissue were collected from sites 25, 50 and 75% along the length of the small intestine for determination of mucosal thickness (MT), crypt depth (CD), villous height (VH) and villous width (VW). Zinc oxide supplementation altered the mucosal morphology of the small intestine. Mucosal thickness (P < 0.08) and VH (P < 0.05) were increased at sites 25 and 50% along the length of the small intestine by ZnO supplementation. Overall VW also increased (P < 0.01) with ZnO supplementation. Crypt depth decreased (P < 0.05) at 75% along the length of the small intestine with ZnO supplementation. The ratio of VH to CD was higher (P < 0.05) for ZnO-supplemented than for control-fed pigs at sites 25, 50 and 75% along the length of the small intestine. There was no effect (P > 0.05) of supplementary ZnO on bacterial populations in ileal digesta or feces. The present study indicates that supplementing ZnO in starter diets changes the epithelial morphology of the small intestine, which may affect nutrient digestion and absorption in newly weaned pigs. Key words: Pigs, zinc oxide, bacteria, intestinal morphology