Effects Of Coated Zinc Oxide On Intestinal Immunity And Microbiota In Weaned Piglets

The present study was conducted to test effects of coated zinc oxide on growth performance, diarrhoea index, intestinal mucosal morphology, intestinal immunity and microbiota of weaned piglets, as well as the absorption and deposition of zinc in piglets. Eighty-four weaned crossbred (Duroc×Landrace×Yorkshire) piglets of 28±1 d of age averaging 7.72±0.65 kg of initial BW were randomly allotted to seven treatment groups, with four replicates per group and three piglets per replicate, as follows:a low Zn group fed diet containing 250 mg Zn/kg from ZnO (LZ), a high Zn group fed diet containing 2250 mg Zn/kg from ZnO (HZ), and five experimental groups in which coated ZnO was added at 250(CZ250),380(CZ380),570(CZ570), 760(CZ760),1140(CZ1140) mg Zn/kg of basal diet, respectively. The trial lasted 28 days, and in 15-28 d zinc dose of HZ group decreased to 250 mg Zn/kg from ZnO. On the morning of d 15 and d 29, the samples were collected after piglets were slaughtered under anesthesia. The results indicated that,1. During the period of d 1 to d 14, there were quadratic and cubic effects of zinc oxide dose on diarrhoea index of piglets (P<0.01); compared with LZ, coated ZnO (380 and 570 mg Zn/kg) reduced (P<0.05) diarrhoea index in 1-14 d, which both had no differences with that of HZ. During the period of d 15 to d 28, there were linear effect of zinc oxide dose on diarrhoea index of piglets (P<0.01).2. Compared with LZ, CZ380 and CZ570 increased duodenal villus height and the ratio of villus height and crypt depth (P<0.05); CZ570 also increased jejunal villus height and the ratio of villus height and crypt depth (P<0.05), and decreased jejunal crypt depth; CZ380 and CZ570 upregulated IGF-1 mRNA levels in jejunum mucosa (P<0.05).3. Compared with LZ, CZ380 and (or) CZ570 upregulated mRNA levels of tight junction ZO-1, occludin, and anti-inflammatory cytokines IL-10, TGF-β1 (P<0.05), downregulated mRNA levels of pro-inflammatory cytokines TNF-a (P<0.05), and elevated SIgA concentration in jejunum mucosa (P<0.05).4. Compared with LZ, CZ380 decreased (P<0.05) the microbiota richness and Shannon diversity index in jejunal contents and faeces, of which the microbiota richness in faeces of CZ380 had no difference with that of HZ, while others were lower than that of HZ (P<0.05). In addition, compared with LZ, CZ380 and CZ570 increased the relative abundances of Lactobacillus and E. coli, while HZ decreased the relative abundance of Lactobacillus, increased that of E. coli (P<0.05).5. No significant differences were observed in Zn concentrations of serum, liver and kidney of piglets between all coated ZnO groups and LZ group (d 14 and 28), while the above parameters of HZ were higher (P<0.05) than those of LZ (d 14). After two weeks when zinc addition concentration of HZ decreased to that of LZ (d 28), Zn concentrations in serum and liver were also higher than those of LZ. Zn concentrations in stomach, jejunal, colonic contents, and faeces increased linearly (P <0.01) with increasing addition levels of coated ZnO, while the above parameters of HZ were higher (P<0.05) than those of coated ZnO.In all, coated zinc oxide (380 and 570 mg Zn/kg) can alleviate diarrhoea by improving intestinal morphology, promoting gene expression of intestinal epithelial tight junctions, increasing intestinal mucosa SIgA concentration, regulating gene expression of intestinal mucosa inflammatory cytokines, and intestinal microbiota composition. Compared with high concentration of zinc oxide, coated ZnO (380 and 570 mg Zn/kg) had no effects on zinc concentrations of serum, liver and kidney of piglets, and avioded the accumulation of excessive Zn in animals, reduced the Zn concentration of excreted faeces.