The present study was carried out to evaluate the pharmacological effect of Zn in diarrhoea in relation to intestinal permeability. Seventy-two weaning piglets, aged 24 d, were allocated to three dietary treatments: (1) control diet without supplemental Zn; (2) control diet supplemented with 2000 mg Zn/kg from ZnO; (3) control diet supplemented with 2000 mg Zn/kg from tetrabasic zinc chloride (TBZC). At the end of a 14 d experiment period, piglets were weighed, feed consumption was measured, and mucosal barrier function was determined using the lactulose/mannitol test. Expression of mucosal tight junction protein was measured at RNA and protein level. Inclusion of TBZC or ZnO in the diet significantly increased average daily gain (P < 0·01) and average daily feed intake (P < 0·05), while leading to reduced feed conversion ratio (P < 0·05) and faecal scores (P < 0·01). TBZC reduced urinary lactulose:mannitol ratios of weaning piglets (P < 0·05), while dietary supplementation with ZnO tended to reduce urinary lactulose:mannitol ratios (P = 0·061). ZnO or TBZC significantly enhanced the mRNA and protein expression of occludin (P < 0·05) and zonula occludens protein-1 (ZO-1) (P < 0·05) in the ileal mucosa. Piglets fed the TBZC-supplemented diet had a higher level of occludin than pigs fed the ZnO-supplemented diet (P < 0·05). The results indicate that Zn supplementation decreased faecal scores and the reduction was accompanied by reduced intestinal permeability, which was evident from the reduced urinary lactulose:mannitol ratios and increased expression of occludin and ZO-1. Therefore, the protective effect of pharmacological levels of dietary Zn in reducing diarrhoea might, at least partly, be associated with reduced intestinal permeability.
