Mixed organic acids as antibiotic substitutes improve performance, serum immunity, intestinal morphology and microbiota for weaned piglets

The objective of this experiment was to evaluate the effect of two mixed organic acids (OA) on performance, serum immunity, intestinal morphology and microbiota of weaned pigs in comparison with antibiotic growth promoters (AGP). A total of 144 weaned piglets [Duroc × (Landrace × Yorkshire), average weight 8.63 ± 1.56 kg] were randomly allocated to 1 of 4 dietary treatments with 6 replicate pens per treatment (3 barrows and 3 gilts per pen). The dietary treatments included a corn-soybean basal diet (CTR), AGP diet (CTR + 10 mg/kg zinc bacitracin, 5 mg/kg colistin sulphate and 5 mg/kg olaquindox), Organic acid 1 diet [OA1; CTR + 3000 mg/kg OA1; a synergistic blend of free and buffered short chain fatty acids (mainly formic acid, acetic acid and propionic acid) combined with medium chain fatty acids (MCFA)]. Organic acid 2 diet (OA2; CTR + 2000 mg/kg OA2; a synergistic blend of a phenolic compound, slow release C12, target release butyrate and sorbic acid, MCFA and OA). Compared with CTR, average daily gain (ADG) and feed efficiency (FE) were improved (P < 0.05) by OA2 in phase 2 (d 14-28) and the overall period (d 0-28), and OA1 improved (P < 0.05) FE during the overall period, while AGP increased (P < 0.05) ADG and FE in phase 2. Both OA1 and OA2 reduced (P < 0.05) the incidence of diarrhea and fecal E. coli counts. The apparent total tract digestibility (ATTD) of total carbohydrates, neutral detergent fiber (NDF), acid detergent fiber (ADF) and phosphorus was improved (P < 0.05) by OA2 in phase 1 (d 0-14). In phase 2, OA1 increased (P < 0.05) ATTD of dry matter, total carbohydrates, NDF and ADF while OA2 improved (P < 0.05) ATTD of total carbohydrates, phosphorus and ether extract. Compared with CTR, the concentration of total volatile fatty acid in feces was improved (P < 0.01) in pigs supplemented with AGP, OA1 and OA2. The concentration of IgG, growth hormone, and total antioxidant capacity in serum tended to be higher, and the amount of hydroxyl radicals in serum was lower (P < 0.05) in pigs supplemented with OA2 compared with CTR. Crypt depth in the jejunum for piglets fed with OA2 was lower (P < 0.05), and the ratio of villus height to crypt depth in the jejunum and ileum was greater (P < 0.05) in pigs fed with AGP, OA1 or OA2 than those of CTR. The results from the present research indicate that OA1 and OA2 can be used to replace AGP based on the positive effects on performance, serum immunity, intestinal morphology and microbiota in the weaned piglets.