Abstract: 【Objective】 The objective of this experiment was to compare the effects of different types of benzoic acid on growth performance,serum biochemical indices,pH in gastrointestinal contents and intestinal flora of weaned piglets.【Method】 A total of 72 Duroc ×Landrace ×York weaned piglets at aged of 23 days were allotted to 3 groups according to body weight (mean body weight 6.44 kg±0.23 kg) with 6 replicates,and 4 pigs (2 barrows and 2 gilts) per replicate.The pigs in control group were fed a basal diet,while in benzoic acid group (BA group) were fed the basal diet supplemented with 0.5% benzoic acid,and in controlled-release-coated benzoic acid group (CBA group) were fed the basal diet supplemented with 0.3% controlled-release-coated benzoic acid.The experiment lasted for 42 days,which was divided into two stages:Days 1 to 14 and days 15 to 42.Body weight of each piglets were weighed on the 1st,15th and 42th day of the trial period,feed intake and the fecal morphology were recorded each day,the blood were collected on the 14th day,and the gastrointestinal chyme and urine were collected on the 42th day,the performance,diarrhea degree,the activities of diamine oxidase (DAO),glutathione peroxidase (GSH-Px),catalase (CAT) and superoxide dismutase (SOD),the contents of malondialdehyde (MDA) and D-lactic acid(D-LA),the pH of gastrointestinal chyme and urine,the count of Lactobacillus,Escherichia coli,total bacteria in ileum and caecum were detected.【Result】 Compared with the control group,① the ADG and ADFI of piglets in 1-42 and 15-42 days were significantly increased in BA and CBA groups (P＜0.05),and the F/G of piglets in CBA group was significantly decreased at all stages (P＜0.05).② The diarrhea index of piglets in 1-14 days was significantly decreased in BA group (P＜0.05),and the diarrhea rate and diarrhea index of piglets in 1-14 and in 15-42 days were significantly decreased in CBA group (P＜0.05).Compared with BA group,the diarrhea index in 1-14 and 15-42 days and the diarrhea rate in 15-42 days were significantly decreased in CBA group (P＜0.05).③ The pH of digesta in stomach, duodenal and urine of piglets in BA group were significantly decreased (P＜0.05),and the pH of digesta in duodenal,jejunum,ileum and cecum of piglets in CBA group was significantly decreased (P＜0.05).④ The levels of DAO and MDA in serum of piglets in both BA and CBA groups were significantly decreased (P＜0.05),and the activities of GSH-Px,SOD and CAT in serum of piglets were significantly increased (P＜0.05),and the effects in CBA group were significantly better than those of BA group (P＜0.05).⑤ The number of Escherichia coli in ileum and cecum and the total number of bacteria in cecum both in BA and CBA groups were decreased,and the differences in CBA group were significant (P＜0.05).The number of Lactobacillus in ileum and cecum in BA and CBA groups were significantly increased (P＜0.05).【Conclusion】 The results suggest that dietary supplementation of 0.5% benzoic acid and 0.3% controlled-release-coated benzoic acid could promote growth performance and improve intestinal barrier function of weaned piglets.The application effects of 0.3% controlled-release-coated benzoic acid were better than that of 0.5% benzoic acid,which had the advantage of reducing cost and increasing efficiency.

Key words: benzoic acid; controlled-release-coated; weaned piglets; growth performance; intestinal microecology