Effects of fermented rapeseed meal on gastrointestinal morphometry and meat quality of rabbits (Oryctolagus cuniculus)

•Fermented rapeseed meal (FRSM) modifies the development of gastrointestinal tract.•FRSM does not alter the proximate chemical composition of rabbit meat.•The 8-12% proportion of FRSM reduces the pH of rabbit muscles.•FRSM increases collagen content without losing of meat technological usefulness. The aim of the study was to determine effects of three levels of rapeseed meal (4% - FR4, 8% - FR8, and 12% - FR12) which has undergone fermentation and drying processes (FRSM) in the diet of crossbred rabbits (New Zealand White × Popielno White, n=40) on their gastrointestinal tract morphometry, internal organs weight, and proximate composition and physicochemical properties of skeletal muscles (biceps femoris – BF, and joined longissimus thoracis and longissimus lumborum – LTL). Although the total length of the digestive tract of rabbits did not differ significantly, the addition of FRSM was found to significantly (P < 0.01) affect the lengthening of caecum (between 0.73 and 0.91 m) and large intestine (from 1.07 to 1.24 m) in comparison to the control group (0.31 m and 0.54 m, respectively). Additionally, the diet with FRSM significantly (P < 0.05) influenced the weight of the heart, whereby the lightest hearts was found in the control group (10.0 g) and the heaviest in group FR8 (14.03 g). The content of proximate chemical constituents in rabbit muscle tissues was similar, with except of collagen percentage. A larger share of FRSM (from 4% to 12%) was accompanied by an increased level of collagen in LTL (P < 0.01), from 0.33% in group C to 0.46% in group FR12. In BF muscle the significantly (P < 0.01) highest collagen content was found in FR4 (2.27%) and the lowest in FR12 (0.88%). The significant decrease in the ultimate pH of LTL (from 5.71 to 5.62) and water-holding capacity (from 44.5 to 49.2 mg) as the share of FRSM in the diet increased were observed in comparison with the group C (5.74 and 37.9 mg, respectively). These effects were not noted in the BF muscle of the rabbits. A diet with FRSM significantly affected all colour parameters (CIE L*, a*, b*, C*, and h°) of the LTL and the yellowness (b*) and saturation (C*) of the BF muscle. The lightness (L*) of LTL muscles was significantly (P < 0.05) higher in the experimental rabbits, irrespective of the level of FRSM (51.50 ≤ L* ≤ 52.61), than in the control group (L*=47.51). The increased content of collagen (between 4.9 and 5.4 mg/g) and shear force (between 25.4 and 37.7 N) for cooked LTL compared to