# Effect of Benzoic Acid on Nutrient Digestibility and Rectal Microbiota of Weaned Holstein Dairy Calves

## TL;DR

Adding benzoic acid to the diet of weaned dairy calves improves gut health and bile acid production without affecting nutrient digestion.

## Contribution

This study shows that benzoic acid improves rectal microbiota and intestinal health in weaned calves without affecting nutrient digestibility.

## Key findings

- Benzoic acid increased Bifidobacterium and Bifidobacterium pseudolongum in rectal microbiota.
- Benzoic acid decreased Clostridium sensu stricto 1 and enhanced primary bile acid biosynthesis.
- Benzoic acid had no effect on apparent nutrient digestibility in calves.

## Abstract

Our previous study has shown that supplementation of 0.50% benzoic acid (BA) increased growth performance, promoted rumen fermentation, and improved rumen microbiota’s composition and functional traits. This study further evaluated supplementation of 0.50% BA on the apparent nutrient digestibility and rectal microbiota of weaned Holstein dairy calves. The results showed that BA supplementation had no impact on apparent nutrient digestibility, but it improved intestinal health by increasing the relative abundances of Bifidobacterium and Bifidobacterium pseudolongum, while decreasing that of Clostridium sensu stricto 1, and, finally, it enhanced primary bile acid biosynthesis. This study indicates that BA may be an effective additive in the rearing of dairy calves during and after weaning.

Our previous study has shown that supplementation of 0.50% benzoic acid (BA) increased growth performance, promoted rumen fermentation, and improved the composition and function of rumen microbiota. This research was designed to conduct a deeper exploration of the impacts of dietary supplementation with BA on the apparent digestibility of nutrients and the composition of rectal microbiota in weaned Holstein dairy calves. Sixteen Holstein heifer calves with similar body weights (91.2 ± 0.7 kg) were selected and randomly allocated into two groups, each comprising eight calves. Calves in the control group (CON group) were fed with a basal diet, while those in the benzoic acid group (BA group) were fed with the basal diet supplemented with 0.50% benzoic acid (on a dry matter basis). The experimental period started at 60 days of age and ended at 102 days of age, lasting for a total of 42 days. The calves were weaned at 60 days of age, with a transition period of 7 days. Feed samples were collected every two weeks, fecal samples were collected from 99 to 101 days of age, and blood samples were collected at 102 days of age. The results showed that supplementation with BA did not influence the digestibility of dry matter, crude protein, ether extract, neutral detergent fiber, acid detergent fiber, calcium, and phosphorus between the two groups. Compared with the CON group, BA supplementation tended to decrease the total cholesterol (TC) in the serum of the calves (p = 0.067). Supplementation with BA increased the relative abundances of the two beneficial bacteria, Bifidobacterium and Bifidobacterium pseudolongum (p < 0.05, LDA > 2), but decreased that of the harmful bacterium, Clostridium sensu stricto 1, in the rectum of dairy calves. The microbial functional prediction revealed that the fecal microbial metabolism involved in primary bile acid biosynthesis was higher in the calves from the BA group. In conclusion, the present study demonstrated that adding 0.50% BA to the diet did not influence the apparent nutrient digestibility, but improved rectal microbiota health, which finally promoted the growth performance in weaned Holstein dairy calves.