Benefits to microbial fermentation in the colon and as a consequence less flatulence can be promoted for the health of adult dogs according to the amount and protein source. The present study evaluated different protein sources in dry food for brachycephalic dogs regarding microbial fermentation and nutrient digestibility. Four dry dog foods with similar protein content were formulated for adult maintenance: poultry meal (PM) diet; wheat gluten (WG) diet; PM + WG diet; and PM + WG + hydrolysed protein (HP) diet. Eight French bulldog adult dogs were arranged in a 4 × 4 Latin square design during the 28 d trial. Fresh faeces were collected for assessment of nutrient digestibility and analyses of faecal pH, SCFA, biogenic amines, ammonia and lactate. Means were compared by the PROC MIXED procedure of SAS and by Tukey's test, considering P ≤ 0·05. The animals fed the WG and PM + WG diets showed higher digestibility for DM (P < 0·05), organic matter (P < 0·05), crude protein (P < 0·001) and lower faeces production (P < 0·02) than the PM and PM + WG + HP diets. Feeding diet PM + WG + HP resulted in lower faecal score and pH (P < 0·05) compared with other diets. Concentrations of fermentation metabolites were not statistically significantly different among diets. In conclusion, WG alone or in combination with PM improved protein and DM digestibility. Fermentation products were not affected by protein source.