| This experiment was conducted to investigate the effects of adding organic acids in diet and drinking water on growth performance,gastrointestinal p H,serum biochemical indicators,apparent nutrient digestibility,and SIgA content in the jejunum mucosa of weaned piglets.A total of 120 healthy 21-day-old(6.0 ± 1)kg DLY weaned piglets were randomly allotted 4 groups with 6 replicates per group and5 piglets per replicate.The four groups were NC,PC,SPT,and FPT,respectively.NC was the control group and fed basic diets.PC was the antibiotic group,and 0.05%virginiamycin premix(50% virginiamycin content)was added to the basic diet.SPT is an organic acidifier group,which adds 0.2% of compound organic acid B(the main ingredients are sodium butyrate,hexanoic acid,caprylic acid,capric acid,lauric acid)to the basic diet,and 0.1% of compound in drinking water.Organic acid A(main ingredients are formic acid,ammonium formate,acetic acid).FPT is an organic acidifier group,which adds 0.2% of compound organic acid B and 0.3% of compound organic acid C(main components formic acid,ammonium formate,acetic acid)to the basic diet.The results showed as follows:1)Growth performance and digestibility.FCR of FPT group decreased by12.94% and 13.45% compared with NC、PC.The diarrhea rate was lowest in SPT group,and decreased by 39.85% and 17.53% in NC、PC group.moreover,the diarrhea rate in the FPT group was 19.55% lower than that in the NC group.in addition,the mortality rate was the highest in the PC group during the trial dead pigs in the SPT group,but there was no significant difference in the above growth performance results(p>0.05).However,there was no significant difference in apparent digestibility of crude fiber and fat and crude protein in the four treatment groups(p>0.05)Meanwhile,there was no significant effect on trypsin activity and a-amylase activity in piglet jejunal contents(p>0.05).The lipase activity of SPT group was significantly higher than that of NC、PC group,which increased by 47.09% and 13.55% compared with NC group and PC group,respectively,and there was a significant difference(p<0.05).but FPT group showed a decrease in lipase activity compared with NC and PC groups(p>0.05).moreover,lipase activity in PC group showed a trend of improvement compared with NC group,but there was no significant difference(p>0.05).2)Effects of on blood biochemical indicators.The content of alkaline phosphatase decreased by 58.59% and 58.37% in SPT、FPT group compared with NC group(p<0.01).The content of alkaline phosphatase in serum of SPT、FPT group decreased significantly by 25.87% and 25.70%(p<0.05)compared with PC.Moreover,compared with NC,the alkaline phosphatase content in PC group also decreased significantly(p<0.05).moreover,the alanine aminotransferase content in SPT group decreased by 86.01% compared with NC group(p<0.05).and FPT group There was no significant difference in TNF-a content compared with NC、PC、SPT group,but there was a decreasing trend(p>0.05).The total protein concentration in the SPT group was higher than that in the NC、PC、FPT group,but there was no significant difference(p>0.05)3)Effects on intestinal flora.the thick-walled phylum SPT、FPT colon chyme in the test group was 15.55% and 5.43% higher than that in the NC group,and 18.06%and 7.72% higher than that in the PC group,respectively.The results showed that SPT、FPT test group decreased 32.56%,8.44%,35.13% and 11.92% respectively compared with NC group.the ACE diversity index,observed＿species diversity index value of SPT group was higher than that of the colonic microbiota,i.e.,SPT.Group intestinal microflora diversity is higher,and the difference between the two is significant(p<0.05).moreover,there was no significant difference in Alpha diversity index values compared with NC in the FPT group(p>0.05).NC had high similarity with PC group of microbial community composition,while SPT、FPT group was significantly alienated from NC、PC group,and the degree of SPT and FPT group overlap was low,which indicated that the composition of the group was different.4)Effects of on other intestinal indicators.SPT、FPT group significantly decreased the p H of gastric and duodenal contents compared with PC group(P <0.05).the content of SIgA in jejunal mucosa was significantly increased in the organic acid SPT、FPT group compared with the NC group and the PC group(0.05 p<).The height of duodenum and jejunum villi in SPT、FPT group was significantly higher than that in NC、PC group(p<0.05).However,there was no significant difference in the contents of propionic acid and butyric acid(p>0.05).The acetic acid and isoamyl in SPT and FPT groups There was significant difference in acid content(p<0.05),FPT group was 19.64% higher than SPT group.The content of valerate in compound organic acid SPT 、 FPT group increased 46.36%,64.49%,39.03% and 56.26%,respectively,compared with PC group,and there was significant difference between compound organic acid group and NC group and PC group(p<0.05).the content was highest in SPT group and lowest in FPT group.SPT group increased by26.50%,38.87% and 42.81% compared with NC group,PC group and FPT group,respectively.there was no significant difference in hexanoic acid content compared with NC and PC groups(p>0.05),but there was an increasing trend.In conclusion: adding compound organic acids and antibiotics to feed and drink water of weaned piglets had no significant effect on growth performance of weaned piglets.Adding compound organic acid can improve the abundance of intestinal flora and microorganism,increase the secretion of intestinal SIgA and promote the development of intestinal tract.However,the effects of adding different compound acidifiers on the composition of microorganisms and the contents of acetic acid and valerate in intestinal contents were different.And for 21-day-old weaned piglets,the addition of complex organic acids in the diet and drinking water has a better anti-diarrhea effect. 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