The aim of the present study was to evaluate the interactive effects of the inclusion of wet corn grain preserved with organic acids (CP) and soybean meal (SBM) substitutes, including solvent-extracted low erucic acid, low glucosinolate rapeseed meal (RSM) and peas (PEA), in broiler diets. A total of 171 eight-day-old female Ross 308 broilers were distributed into 9 groups, each consisting of 19 birds kept in individual cages. During the 27-day feeding period, the birds received wheat-corn-SBM diets and were arranged in a 3 × 3 factorial design; the factors included corn treatments (CP, heat-dried corn moisture-reconstituted with water (CDW) or with preservative (CDP)) and three protein sources (SBM exclusively or mixed with RSM or PEA at the level of 150/200 g/kg diet). The feed intake and body weight gain declined in birds fed the RSM diet (P < 0.01), while corn treatments had no significant effects on the performance of the broilers. The RSM diets increased bacterial enzyme activity in the ileal and caecal digesta (P < 0.001) and decreased butyrate, acetate and total short-chain fatty acid (SCFA) concentrations in the caecal digesta (P < 0.001) compared with the values detected in the case of the SBM and PEA diets. Corn treatments had negligible effects on the bacterial enzyme activity of ileal and caecal microbiota but induced a decline in lactate concentrations in the ileum in the case of the diets with CP and CDP corn (P < 0.049). Our findings indicate that peas at the level of 150/200 g/kg are a good alternative to SBM, while diets with the same level of RSM may have an adverse effect on growth performance and acetate and butyrate production in the caecum. CP up to the level of 300 g/kg diet and peas can be used with no adverse effects on gut physiological status and the growth performance of broilers and provide an opportunity to include locally available grains in poultry rations.