Effect of dietary soluble fibre level and n-6/n-3 fatty acid ratio on digestion and health in growing rabbits

Abstract

The aim of this work was to study whether the dietary supplementation with soluble fibre (SF) and the reduction of the n-6/n-3 fatty acid ratio or the combination of both influence the digestion and immune response in young rabbits after weaning. Four diets in a 2 × 2 factorial arrangement were used with two levels of SF (78 vs. 130 g/kg, on dry matter basis; high soluble fiber [HSF] and low soluble fiber [LSF]) and two different n-6/n-3 fatty acids ratio (13.4/1 vs. 3.5/1). Rabbits (New Zealand white ☓ California hybrid) came from multiparous rabbit does fed with the same diets described. Two experiments were carried out to study the mortality during fattening of group-caged rabbits fed the experimental diets from 26 to 39 days of age and then a common commercial diet using 517 rabbits weaned at 26 days of age, or fed the commercial diet during the whole fattening period to test the potential influence of the experimental diets when offered only before weaning (using 833 rabbits). In a third experiment, faecal digestibility (39–42 days of age; 56 rabbits) and soft faeces excretion were determined. In a fourth experiment, ileal digesta was collected at 39 days of age to determine the nutrient ileal digestibility (using 224 rabbits), weight of digestive organs, caecal pH (using 144 rabbits) and mucosa from the ileum and appendix to study the immune response (32 rabbits). Mortality decreased (P = 0.049) in rabbits fed the HSF diets until the first phase of fattening, with no influence of the n-6/n-3 ratio, whereas no differences were observed among treatment groups fed with the experimental diets only before weaning. The increase of SF improved the ileal and faecal digestibility of total dietary fibre (TDF; P ≤ 0.029). The increase of the n-6/n-3 ratio impaired the faecal TDF and soluble fibre digestibility only in rabbits fed low SF diets (P < 0.05). Rabbits fed high SF diets tended to have a higher ileal starch digestibility and ileal flow of mucins compared with those fed low SF diets (P ≤ 0.064). Rabbits fed HSF diets showed a lower ileal MUC-13 and iNOS gene expression (P ≤ 0.046) than those fed LSF diets. In conclusion, the increase of the level of SF reduced the mortality rate probably due to an improved intestinal health, whereas the incorporation of n-3 fatty acids showed no relevant effects.