Effect of supplementation of a blend of protected aromatic compounds including benzoic acid (BPAC) on weaned piglets’ diets as alternative to Zinc Oxide: growth performance and faecal microbial profile

Oraganic acids (OA), especially benzoic acid, have long been used for their wide antimicrobial activity and have shown to promote intestinal health and improve body weight gain, feed intake and feed conversion ratio of pigs when supplemented in their diets. On the other side, the European Commission decided recently to ban the use of pharmacological levels zinc oxide (ZnO) in diets for this animal species as from 2022. The aim of this study was to investigate the effect of a blend of protected aromatic compounds including benzoic acid (BPAC) 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 commercial farms which routinely use ZnO. For each farm, piglets were allocated to one of the two experimental groups: i) piglets receiving a commercial diet supplemented with 2.5 g/kg of ZnO; ii) piglets receiving the same commercial diet but supplemented with 2.5 g/kg of BPAC. Piglets were blocked to each diet based on body weight (BW) and sex, and 1720 piglets were allocated to the ZnO treatment, while 1728 animals were allocated to the BPAC one. The animals received the treatment for a total of 6 weeks and the feed supplements were added in both the creep feed (from day (d)7 of life to weaning) and the pre-starter diets (from weaning to 6 weeks of life). Cumulative performance from d0 (weaning) to 6 weeks post-weaning was calculated, and mortality and diarrhea incidence were recorded. Faecal pool samples were collected from 8 box replicates per group from each farm to characterize the microbial profile. Piglets in BPAC treatment showed higher average daily gain (ADG) (P <0.01) and lower feed conversion ratio (FCR) (P <0.05) in all the farms compared with animals in the ZnO treatment and there were no differences for feed intake (FI) between the two treatments. A reduction of mortality and diarrhea incidence was observed in pigs from the BPAC treatment compared to those in the ZnO one (P <0.01). The faecal microbiota was characterized by a higher alpha diversity (Shannon: 4.52 vs 4.1, P <0.01; invSimpson: 36.1 vs 24.5 P <0.01) in the BPAC treatment. The PERMANOVA test showed that the microbial composition was significantly influenced by the treatment factor (P <0.01, R2= 0.03). Animals in the BPAC treatment were characterized by a higher abundance of Ruminococcus (P adj <0.01), Prevotellaceae (P adj <0.01) and Fibrobacteraceae (P adj <0.05), known for their fiber fermenting abilities. In conclusion, the supplementation with a blend of protected aromatic compounds including benzoic acid positively influenced the microbial profile of weaned piglets by increasing the alpha diversity, and by favouring the proliferation of known beneficial bacteria, related with 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 this protected in-feed solution based on benzoic acid.