Dietary protein and carbohydrate modify volatile fatty acid (VFA) profile in canine faeces

Microbiota inhabiting the colon fermentate carbohydrates, proteins and endogenous substrates to volatile fatty acids (VFA) and produce energy for the microbial growth. Because all species of bacteria ferment some component of the digesta and produce various VFAs, alterations in microflora may modify these fermentative end products. Thus, measuring the amount and type of VFA produced gives an instrument which reflects changes in the bacterial microbiota of the intestine. This study set out to explain the connections between diet composition and the formation of VFAs. The general hypothesis was that different food compositions cause differences in the VFA profile, and this may have systemic effect on animal health. Graeco Latin Square design study with 5 healthy Beagles was performed, feeding high protein (diet A, starch 54 g/kg, crude protein 609 g/kg), high carbohydrate (diet B, starch 438 g/kg, crude protein 194 g/kg), and a balanced commercial (diet C, starch 277 g/kg, crude protein 264 g/kg) diets for three weeks each. The diet C was used also for the baseline. VFA, fecal dry matter and fecal consistency score were assessed. All dogs had formed feces during diets B and C but diarrhea during diet A, leading to significant differences in fecal consistency score between the diets (p < 0.0001). The results indicate that alterations in diet had a large influence on the amount and quality of VFAs produced. Mixed-effect model analysis shows that the diets had a statistically significant (p<0.05) influence on all of the VFAs produced excluding butyric acid. The most significant changes from the baseline diet were seen with the high protein diet. Compared to the baseline diet, valeric acid production increased 24-fold, isobutyric acid by 79.5% and isovaleric acid by 42.4 %. Production of propionic acid decreased by 43.3%, acetic acid by 25.0%, and butyric acid by 10.2 %. In previous studies similar changes in VFA profile have been coupled with various intestinal diseases as well as inhibition in biotin absorption. Furthermore, this might have an influence on inflammatory response at the cellular level. Thus, changes in VFA profile may have an influence at least on the local intestinal health. The total amount of fatty acids decreased on both experimental diets. It seems that having moderate protein and carbohydate levels in the diet is a virtue and more is not necessarily better. This study provides additions to existing understanding of the relationship between diet composition and the formation of VFAs in the intestine. The findings suggest that observing the alterations in VFA levels formed in the intestine and therefore present in feces, may provide an instrument to indirectly observe changes in the bacterial microbiota of the intestine. Thus, there is a need to find the link between the changes in VFA profiles and colonic microbiota, and bacterial diversity in feces by using molecular methods. Having this greater level of understanding would lead to more robust insights into the role of intestinal microbiota in animal health, and to potential advances in the prevention and curing of related diseases.