By-products of biofuels production such as rapeseed cake and dried distillers' grains with solubles (DDGS) may constitute valuable feedstuffs for livestock. The objectives of the study were to determine the usability of these components in the feeding of growing rabbits and to assess their impact on physiological changes in the gastrointestinal tract of the animals. Sixty-four rabbits were divided into four feeding groups: Control (5% soyabean meal [SBM] in the diet), R (5% rapeseed cake [RSC]), DDGS (5% wheat DDGS), and R/DDGS (2.5% RSC and 2.5% wheat DDGS). The study included a production experiment, a digestibility-balance experiment and physiological assessment of the functioning of animals' gastrointestinal tract (small intestine, caecum and colon). No statistically significant differences were determined in production results of the rabbits. Digestibility of nutrients and energy and nitrogen retention were the highest in the Control and the lowest in Group DDGS. Group DDGS was characterised by the highest relative weight of small intestine and digesta. In turn, Group R was characterised by the highest degree of caecal digesta hydration and bulking and by the highest pH value and the lowest concentration of VFA in caecum. The activity of selected bacterial enzymes released to the caecal environment was similar in all groups; however, the activity of α-arabinopyranosidase was significantly increased in Groups R and DDGS. Worthy of notice is the enhanced enzymatic activity of colonic microbiota in the R/DDGS group which has a positive effect upon increased utilisation of dietary nutrients compared to the DDGS group. The obtained results indicate that SBM from rabbit diets may be successfully replaced by 5% RSC as well as by 2.5% RSC + 2.5% wheat DDGS.
Keywords: digestibility; distillers’ grains; nitrogen metabolism; performance; rabbit feeding; rapeseed.