The effects of synergistic blend of organic acid or antibiotic growth promoter on performance and antimicrobial resistance of bacteria in grow–finish pigs

This study was carried out to evaluate the effect of Selacid Green Growth (GG) or antibiotic growth promoter (AGP) on the performance and economics of grow–finish (GF) pigs. The Selacid GG is a blend of short-chain fatty acids (formic acid, acetic acid, lactic acid, propionic acid, citric acid, and sorbic acid), buffered organic acid (ammonium formate), and a combination of medium-chain fatty acids (C8, C10, and C12). A total of 312 grower pigs (Yorkshire × Landrace × Duroc) with initial body weight (BW) of 26.5 ± 0.92 kg were used in a 90-d feeding trial. The pigs were allocated randomly to three treatments consisting of eight replicate pens with 13 pigs each. The treatments tested included a 1) negative control (control): basal diet without colistin and Selacid GG, 2) positive control (AGP): basal diet with colistin (20 g/ton), and 3) Feed additive (Selacid GG): basal diet with Selacid GG (2 kg/ton). The results showed that, over the entire period of the experiment, the dietary supplementation of Selacid GG elicited a similar effect as AGP on feed cost and on all growth parameters measured (P > 0.05). In relation to the control group, Selacid GG significantly improved the final BW (+3.4 kg or 3.6%), average daily gain (+39 g/pig or 5.3%), and gain:feed (+30 g or 8.1%) of pigs (P < 0.05). In addition, the feeding of Selacid GG reduced feed cost (−0.078 USD) per kilogram BW gain. The average daily feed intake was not affected by dietary treatments (P > 0.05). Escherichia coli was prevalent in 46 out of 48 fecal samples tested. All E. coli isolates were resistant to colistin, amox-colistin, ciprofloxacin, and enrofloxacin. The number of E. coli isolates resistant to amoxicillin/clavulanic, cefotaxime, ceftiofur, and norfloxacin was significantly reduced, whereas the inhibitory zones of amocxillin/clavulanic acid were increased; and the susceptibility of E. coli to amoxcillin/clavulanic, cefotaxime, ceftiofur, ciprofloxacin, nofloxacin, and flumequin was increased when Selacid GG was added in the feeds (P < 0.05). The findings of the study suggest that Selacid GG is a cost-effective product with the same efficacy as AGP in promoting the growth and economic performance of GF pigs. The product is safe and can be added to the diet of GF pigs without developing resistance to selected antibiotics.