Effect of embedded benzoic acid on weaned piglets' growth performance and faecal microbial profile.
The addition of Benzoic acid to weaners diet has shown beneficial effects on growth performance. The aim of this study was to investigate the effect of a embedded benzoic acid (BezAc) used as substitute of supra-nutritional Zinc Oxide (ZnO), on piglets' growth performance and on gut microbiota profile. The trial was conducted in 4 commercial farms which routinely used ZnO. For each farm, piglets were allocated to one of the two experimental groups: i. received a commercial diet supplemented with   2.5 g/kg of ZnO; ii. received the same commercial diet but supplemented with 2.5 g/kg of fat protected Benzoic acid (BezAc). Piglets were blocked to each diet based on body weight and sex. Pigs belonging to the diet ZnO were 1720, pig fed BezAc diet were 1728.  The trial lasted 6 weeks and the additives were supplemented both in the creep feed and in the pre-starter diets. Cumulative performance from d0 (weaning) to 6 week post-weaning was calculated as well as mortality and diarrhea incidence were recorded. In each farm, faecal pool samples were collected from 8 box replicates per group to characterize the microbial profile. Piglets of BezAc group showed higher average daily gain (ADG) (p <0.01) and lower feed conversion ratio (FCR) (p <0.05) in all the farms compared with ZnO and there was not differences on feed intake (FI). A reduction of mortality and diarrhea incidence was observed in pigs fed BezAc compared to ZnO pigs (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 BezAc. The PERMANOVA test showed that the microbial composition was significantly influenced by the treatment factor (p <0.01, R2= 0.03). The BezAc group was 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 BezAc 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 BezAc.