Replacement of starch by digestible fibre in feed for the growing rabbit. 2. Consequences for microbial activity in the caecum and on incidence of digestive disorders

Caecal fermentative activity and daily bacterial biomass production were compared for two groups of nine rabbits, fed a diet rich in starch (ST, 266 g starch kg−1 dry matter (DM)) or a diet rich in digestible fibre (DF, 271 g hemicellulose + pectin kg−1 DM), but which were similar in acid detergent fibre (ADF) content (205 g kg−1 DM). Caecal volatile fatty acid (VFA) concentrations, measured in vivo in healthy rabbits fitted with a caecal cannula, were significantly higher in the DF group (85.1 mmol l−1) than in the ST group (67.7 mmol l−1). Between 44 and 72 days of age, no change in in-vivo VFA level was recorded for the two diets. Acetate molar proportion decreased from 86 to 72% mostly between 44 and 53 days of age (P = 0.05), and was balanced by a slight increase of both propionate and butyrate proportions. ncentration of diaminopimelic acid (DAPA) was two-fold higher in soft than in hard faeces, and was not significantly affected by diet composition. The mean level of DAPA in bacteria was similar for the two groups of rabbits (19.8 μ mol g−1 DM). The mean bacterial biomass production was two-fold higher in the DF group (13.3 g DM day−1) and accounted for 13% of the feed intake. Although ADF intake was similar for the two groups of rabbits, the animals fed the starch-rich diet showed a higher incidence of digestive disorders (diarrhoea). The partial replacement of starch by digestible fibre improved the health status without major impairment of growth performances.