Impacts of feeding organic acid-based feed additives on diarrhea, performance, and fecal microbiome characteristics of pigs after weaning challenged with an enterotoxigenic strain of <i>Escherichia coli</i>

Abstract

Post weaning diarrhea (PWD) caused by enterotoxigenic strains of <i>E. coli</i> (ETEC) remains a major problem in the industry, causing decreases in performance and survival of weaned pigs. Traditionally, antimicrobials have been used for its mitigation/control. This study tested the hypothesis that a combination of two organic acid (OA)-based commercial feed additives, Presan FX [an OA, medium-chain fatty acid (MCFA) and phenolic compound-based product] and Fysal MP (free and buffered OA based on formic acid), would reduce PWD and improve post-weaning performance in pigs challenged with an F4-ETEC. This combination was assessed against a Negative control diet without any feed additives and a diet containing amoxicillin. Combined with a reduction in temperature during the infection period, inoculation with F4-ETEC resulted in 81% of pigs developing diarrhea, but with no differences between treatments (<i>P</i> > 0.05). However, between days 14 to 20 of the study and due to colonization by <i>Salmonella</i> serovars, pigs fed the combination of Presan FX and Fysal MP showed less (<i>P</i> = 0.014) diarrhea commensurate with a lower (<i>P</i> = 0.018) proportion of <i>Salmonella</i> numbers relative to total bacterial numbers. This caused less (<i>P</i> = 0.049) therapeutic antibiotic administrations relative to the diet with amoxicillin during this time. The diversity of bacteria within amoxicillin-treated pigs was lower (<i>P</i> = 0.004) than the diversity in control or Presan FX + Fysal MP-treated pigs (<i>P</i> = 0.01). Pair-wise comparisons showed that amoxicillin-treated pigs had altered (<i>P</i> < 0.001) fecal microbial communities relative to both Presan FX + Fysal MP-treated pigs and control pigs. Amoxicillin-treated pigs were characterized by an increased abundance of bacterial families generally linked to inflammation and dysbiosis in the gastrointestinal tract (GIT), whereas Presan FX + Fysal MP-treated pigs had an increased abundance of bacterial families considered beneficial commensals for the GIT. Control pigs were characterized by an increased abundance of <i>Spirochaetaceae</i> associated with healthy piglets, as well as bacterial families associated with reduced feed intake and appetite. The combination of two OA-based feed additives did not reduce the incidence of F4 ETEC-associated diarrhea nor enhance performance. However, the combination markedly reduced diarrhea caused by <i>Salmonella</i> that occurred following the ETEC infection, commensurate with less therapeutic administrations relative to the diet with amoxicillin.