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Objectives: Benzoic acid is used in pig nutrition as feed additive with the aim to reduce ammonia emissions in animal husbandry but has also some effects on feed conversion and the intestinal microbial metabolism. However, there are concerns around the safety of benzoic acid at higher inclusion levels. We conducted two trials aiming at the efficacy of benzoic acid at the dietary inclusion level of 5 g per kg feed as well as at the tolerance of piglets to 10 g benzoic acid per kg feed.
Methods: A total of 74 castrated male and female piglets were studied directly after weaning for six weeks. The piglets were allocated to flat decks of 2 piglets per pen and were randomly divided (blocked for gender and weight) onto the treatment groups. In experiment 1 three treatment groups (Control, 0.5%, and 1% benzoic acid) consisting of 18 piglets each were used. In Experiment 2 two treatment groups (Control, and 1% benzoic acid) with 10 piglets each were formed. In both experiments, a typical starter diet for piglets was used containing wheat, soybean meal and barley as the main feed ingredients (19% CP, 13.4 MJ ME/kg). In both trials, health status, growth performance, blood variables, urine pH, post-mortem pathomorphology, and intestinal microbiota were examined.
Results: In experiment 1, both inclusion levels of benzoic acids resulted in a significant higher hippuric acid concentration in urine as well as a reduced urea concentration in blood (p < 0.05) compared to controls. Urine pH was reduced, but neither body weight, feed intake, feed conversion nor the number or seriousness of lesions in the proximal gastrointestinal tract were significantly affected in experiment 1 or 2, respectively. However, up to 50% of colonic and ileal digesta samples of piglets in the control group were found to harbor potentially enteropathogenic Escherichia coli O8, O138, and O141 serogroups in experiment 1. Benzoic acid supplementation led to an up to 100% reduction in occurrence of these serogroups. In experiment 2, most animals exhibited coliform cfu below 104/g digesta in the proximal small intestine in the group receiving benzoic acid, while in the control group most animals harbored coliform cfu above 106/g. In addition, benzoic acid had a significant influence on the intra group similarity of PCR-DGGE banding patterns of the predominant eubacterial and enterobacterial microbiota in colonic and ileal contents in experiment 1. The same observation was made for the eubacterial community in the caecum in experiment 2, while counts of Lactobacillus spp. in the upper part of the small intestine determined by real time-PCR were higher in the benzoic acid group compared to the control group of this experiment. On the other hand, the number of Enterococcus spp. did not differ between the treatment groups. Additional determination of digesta pH, lactate and SCFA revealed no differences between treatment groups in experiment 2.
Conclusions: During the experiments no adverse effects on health of piglets receiving 1% benzoic acid were observed, suggesting the safety of this inclusion level. In addition, the observed modification of the intestinal microbial community composition might be interpreted as beneficial.