Effects of brewer's spent grain and carrot pomace on digestibility, fecal microbiota, and fecal and urinary metabolites in dogs fed low or high protein diets

Laura Eisenhauer, Wilfried Vahjen, Temesgen Dadi, Barbara Kohn, Jurgen Zentek

Brewer’s spent grain (BSG) and carrot pomace (CAP) were used as fiber sources in low or high protein diets in dogs. Ten adult Beagles were involved in five feeding periods of 19 days in a cross-over design. Experimental diets contained 7.5 % of total dietary fiber from BSG or CAP and 20 % or 40 % of crude protein in dry matter. A diet with 3.5 % total dietary fiber from both fiber sources and 20 % crude protein was used as reference. Fecal dry matter was 27 % higher for diets with BSG compared to CAP (P < 0.001). Apparent fecal digestibility of crude protein was 7-11 % higher in diets with 40 % protein concentration (P < 0.001), while apparent digestibility of crude fat was 2–3 % higher for diets with CAP (P < 0.001). CAP increased the apparent fecal digestibility of total dietary fiber, phosphorus and magnesium (P <0.001), while 40 % protein diets had a positive impact on total dietary fiber and sodium and a negative effect on magnesium apparent fecal digestibility (P <0.001). Inclusion of CAP increased fecal short chain fatty acids (P = 0.010), mainly acetate (P = 0.001). I-butyrate (P = 0.001), i-valerate (P = 0.002), biogenic amines (P < 0.001) and ammonium (P < 0.001) increased with higher dietary protein levels. Diet induced changes in the fecal microbiome were moderate. Relative abundance of Bifidobacteriales was higher for the low protein diets (P = 0.001). To conclude, BSG and CAP can be used as fiber sources in canine diets and are well tolerated even at higher inclusion rates, the effect on microbial protein fermentation seems to be limited compared to the dietary protein level.