Replacement of starch by digestible fibre in the feed for the growing rabbit. 1. Consequences for digestibility and rate of passage

Growth performance and nutrient digestibility were compared for two groups of 12 growing rabbits, fed a diet rich in starch (ST, 266 g kg−1 dry matter (DM)) or a diet rich in digestible fibre (DF, 271 g hemicellulose + pectin kg−1 DM), but with similar acid detergent fibre (ADF, 205 g kg−1 DM) and lignin (50 g kg−1 DM) contents. From weaning (day 28) to slaughter (day 72), the average daily feed intake (103 g day−1) and weight gain (34.3 g day−1) were not significantly different between the two groups. The total tract apparent digestibility of organic matter (mean 65.9%) and crude protein (73%) were not significantly affected by the diet. The digestible energy contents of the two diets were similar, although 50% of the starch was replaced by digestible fibres in the DF diet. The daily amount of neutral detergent fibre (NDF) or hemicellulose (HC) degraded was thus 60% higher in the DF group (13.6 g NDF day−1 and 8.3 g HC day−1), whereas the quantity of starch digested was reduced by 50% (9.7 g day−1). te of passage of liquids and particles of the two diets was measured between the caecum and the rectum, for two further groups of nine rabbits fitted with a caecal cannula. The mean retention time (MRT) of the particulate marker (141Ce) between caecum and rectum was 7 h, whereas for the liquid marker (51Cr-EDTA) phase it was 30 h. The passage rates of particles were not affected by the diets; however, the caeco-colic MRT of the liquid phase tended to be lower for the DF diets (−7.1 h, P = 0.14).