Growth, Carcass Quality and Gut Microbiota Responses to Extruded Rapeseed Meal With Protease in Broiler Chickens

BACKGROUND: Soybean meal (SBM) is a major protein source in broiler diets, but its cost and dependence on a limited number of protein sources have increased interest in alternative feed ingredients. Rapeseed meal has considerable potential as an alternative protein source; however, its utilisation is constrained by antinutritional factors that can limit nutrient availability and broiler performance. Extrusion processing and exogenous enzyme supplementation may improve the nutritional value of rapeseed meal. We hypothesised that replacing part of dietary SBM with extruded rapeseed meal (ERSM), in combination with protease and non-starch polysaccharide (NSP)-degrading enzymes, would improve or maintain broiler performance and nutrient utilisation while supporting intestinal health. METHODS: A total of 320 day-old Ross 308 male broiler chickens were randomly assigned to four dietary treatments in a completely randomised design. During the finisher period (22-35 days), birds received a corn-SBM control diet or diets in which 5%, 7.5%, or 10% of SBM protein was replaced with ERSM. All diets contained identical levels of protease and NSP-degrading enzymes. Growth performance, nutrient digestibility, carcass characteristics, intestinal morphology and caecal microbial populations were evaluated to determine the effects of increasing ERSM inclusion. RESULTS: Dietary ERSM affected feed intake (p = 0.029), final body weight (p = 0.017), feed conversion ratio (p = 0.009) and mortality (p = 0.041), with the 5% and 7.5% ERSM treatments generally producing the most favourable performance. Apparent digestibility of dry matter, crude protein, crude fibre, fat and ash was improved in ERSM-fed birds (p < 0.05). Carcass yield, breast weight and thigh weight increased with ERSM inclusion (p ≤ 0.025), whereas liver weight decreased at the highest inclusion level (p = 0.034). ERSM also improved intestinal morphology by increasing villus height and the villus height-to-crypt depth ratio and reducing crypt depth (p ≤ 0.016). In addition, ERSM increased beneficial caecal bacterial populations and reduced Escherichia coli and Clostridium counts (p ≤ 0.050). CONCLUSIONS: Replacing SBM protein with 5%-7.5% ERSM in diets supplemented with protease and NSP-degrading enzymes improved growth performance, nutrient digestibility, carcass characteristics, intestinal morphology and caecal microbial balance in broilers. The findings indicate that appropriately processed rapeseed meal can partially substitute for SBM while maintaining or improving important productive and intestinal health outcomes.