Effect of fibre source on ileal apparent digestibility of non-starch polysaccharides in rabbits

Sixteen New Zealand White X Californian doe rabbits (four per diet) weighing 3397 (s.e. 378) g, and surgically fitted with a glass T-cannula at the terminal ileum were used to determine the apparent ileal digestibility of non-starch polysaccharides of four fibrous foods. Four diets were formulated to contain paprika meal, olive leaves, lucerne hay or soya-bean hulls as the sole source of fibre. Fibre sources were supplemented with different proportions of soya protein isolate, wheat flour, lard, sodium chloride, calcium carbonate, calcium phosphate, DL-methionine and a mineral/vitamin mix, to obtain diets containing at least 185 g crude protein and 50 g starch per kg. All diets included 2 g/kg of the respective fibre source marked with chromium. Diets were assigned to individually caged rabbits in a completely randomized design and were offered ad libitum throughout the experiment. Dry matter intake was not affected by type of diet. Fibre source affected (P < 0.05) corrected ileal apparent digestibility of total non-starch polysaccharides (NSP), xylose, galactose, glucose and uronic acids. Uronic acids were the best digested monomer at the ileum in all the foodstuffs studied, ranging from 0.195 to 0.522 for olive leaves and paprika meal, respectively. Corrected ileal apparent digestibility of uronic acids was correlated with the uronic acids insoluble in NDF solution, expressed as proportion of total uronic acid content (r = -0.74; P = 0.001), the proportion of large particles (> 1.25 mm; r = -0.71; P < 0.01) and the proportion of fine particles (< 0.315 mm; r = 0.65; P = 0.01). Other monomers (arabinose, mannose, rhamnose and galactose) usually related to pectic substances, also showed in general a greater ileal digestibility than that of total NSP. Taking into account the uronic acids content of the diet and their digestibility, digestible uronic acids accounted for 0.572, 0.528, 0.93 and 0.353 of the total ileal digestible NSP of paprika meal, olive leaves, lucerne hay and soya-bean hulls based diets, respectively. The sum of arabinose, mannose, rhamnose and galactose accounted for 0.15 of total NSP digested at the ileum on average, over the different fibre sources studied. Glucose and xylose were the monomers least digested at the ileum. Their corrected ileal apparent digestibilities were close to zero, except for the paprika meal (0.266 and 0.216) and soya-bean hulls (0.137 and 0.057) based diets. In conclusion, the results of this study indicate that a valuable amount of total NSP is hydrolysed before the caecum in rabbits. However, this hydrolysis affects mainly pectic and readily fermentable substances.