Effect of dietary supplementation with a blend of protected aromatic compounds, including benzoic acid, on growth performance and faecal microbial profile of weaned piglets as an alternative to Zinc Oxide

Organic acids (OA), especially benzoic acid, have long been used for their wide antimicrobial activity and have shown to promote intestinal health and increase average daily gain (ADG), feed intake (FI) and feed conversion ratio (FCR) of pigs. On the other side, the European Commission decided to ban the use of harmacological levels of zinc oxide (ZnO) in diets for this animal species from 2022. The aim of this study was to investigate the effect of a blend of protected aromatic compounds including benzoic acid (PBA) as a substitute of supra-nutritional levels of ZnO in piglet diets on growth performance and on gut microbiota profile. The trial was conducted in 4 farms. For each farm, piglets were allocated to one of the two experimental groups: i) piglets receiving a diet with 2.5 g/kg of ZnO; ii) piglets receiving the same diet but with 2.5 g/kg of PBA. Piglets were blocked to each diet based on body weight and sex. 1720 piglets were allocated to the ZnO treatment and 1728 to the PBA. The animals received the treatment for a total of 6 weeks starting from weaning (28 days old). Cumulative performance from weaning to 6 weeks post-weaning were calculated. Faecal pool samples were collected from 8 box replicates per group from each farm to characterize the microbial profile. Piglets receiving PBA showed higher ADG (P <0.01) and lower FCR (P <0.05) in all the farms compared to ZnO, no differences in feed intake (FI) were seen. A reduction of mortality and diarrhoea incidence was observed in pigs from the PBA treatment compared to those in the ZnO (P <0.01). The faecal microbiota was characterized by a higher alpha diversity in the PBA treatment (Shannon: 4.52 vs 4.1, P <0.01; InvSimpson: 36.1 vs 24.5 P <0.01). The microbial composition was significantly influenced by treatment (P <0.01, R2= 0.03). Animals receiving PBA were characterized by a higher abundance of Ruminococcus (FDR <0.01), Prevotellaceae (FDR <0.01) and Fibrobacteraceae (FDR <0.05), known for their fiber fermenting abilities. In conclusion, the supplementation with PBA positively influenced the microbial profile of weaned piglets by increasing the alpha diversity, and by favouring the proliferation of known beneficial bacteria, related to the metabolism of polysaccharides and production of SCFA. These findings on the faecal microbial profile can contribute to explain the higher ADG and lower FCR observed in piglets supplemented with PBA.