Dietary ZnO and arginine supplementation on the dynamic change of microbiota, intestinal morphology, and immune function of weaned pigs subjected to heat stress
Authors: Yoon Se Young , Sa SooJin , Cho Eun Seok , Ko HanSeo , Kim Ga Won , Choi Jung Woo , Kim JinSoo 
Published: April 2020

Abstract
Background. Weaning stress is an economically important problem in the pigs, and the economic loss of the growth performance reduction is even more critical if the heat stress adds to the weaning stress. The supplementation of ZnO is an effective option in reducing the adverse effects of weaning time. This study aimed to investigate the effect of the L-arginine (Arg) inclusion and different doses of ZnO to determine the best dietary supplementation ratio on growth performance, intestinal microbiota and integrity, and immune status in weaned pigs. A total of 180 weaned pigs (28 day-old) were randomly allotted to six treatments with 6 replicate pens in each treatment and 5 pigs per pen. The dietary treatments were: control diet (Con; with 1.1% Arg and without ZnO supplementation); Con + 2500 ppm Zn as ZnO (P-Zn); Con + 1.6% Arg (ARG); Con + 500 ppm of Zn as ZnO + 1.6% Arg (ZnArg1); Con + 1000 ppm of Zn as ZnO + 1.6% Arg (ZnArg2); P-Zn + 1.6% Arg (ZnArg3). Results. The overall result showed that the inclusion of ZnArg3 significantly improved the average daily gain compared with the Con treatment. There was a reduction of feed intake in the Con diet compared with the ZnArg3 diet at phase 1 and overall. At phase 1, the weaned pigs in the ZnArg3 and P-Zn groups exhibited the decreased population of Clostridium spp. in the ileum compared with those of the Con group. In addition, a lower ileal Clostridium spp. population was detected in the ZnArg2 pigs compared with the Con pigs. At phase 2, the colonization of Clostridium spp. was higher in the Con and ARG treatments compared with ZnArg3 treatment. The weaned pigs fed the ZnArg1 and ZnArg3 diets showed a greater villus height of duodenum compared with the Con and P-Zn treatments. The count of eosinophil was significantly higher in the Con and ZnArg1 compared with the ZnArg2 and ZnArg3 treatments. The weaned pigs in the Con group showed increased mRNA expression of HSP27 in the liver compared with the P-Zn, ZnArg1, ZnArg2, and ZnArg3 groups. When fed the basal diet, weaned pigs exhibited enhanced mRNA expressions of IL-6 in the muscle compared with the ZnArg3 group. Dietary supplementation with ZnArg2 decreased the mRNA expressions of IFNγ in the muscle compared with the Con group. Supplementation with P-Zn, ZnArg1, ZnArg2, and ZnArg3 exhibited decreased mRNA expressions of TNF-α compared with the Con group. The mRNA gene expressions of IL-4 were decreased in the jejunum of P-Zn, ARG, ZnArg1, ZnArg2, and ZnArg3 weaned pigs compared with the Con group. The jejunum gene expression of TLR4 was upregulated in the Con and ARG treatments compared with the ZnArg1 and ZnArg3. The ZnArg1, ZnArg2, and ZnArg3 treatments showed a lower mRNA expression of TNF-α compared with the Con group. Conclusion. The Arg supplementation did not improve the growth performance, microbial composition, or immune status of weaned pigs but showed a similar growth performance when supplemented with 500 ppm Zn as ZnO compared with 2500 ppm Zn as ZnO.