REPLACEMENT OF STARCH BY DIGESTIBLE FIBER IN THE FEED FOR THE GROWINGRABBIT .1. CONSEQUENCES FOR DIGESTIBILITY AND RATE OF PASSAGE

Growth performance and nutrient digestibility were compared for two gr oups 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 hemic ellulose + pectin kg(-1) DM), but with similar acid detergent fibre (A DF, 205 g kg(-1) DM) and lignin (50 g kg(-1) DM) contents. From weanin g (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 diff erent between the two groups. The total tract apparent digestibility o f organic matter (mean 65.9%) and crude protein (73%) were not signifi cantly affected by the diet. The digestible energy contents of the two diets were similar, although 50% of the starch was replaced by digest ible fibres in the DF diet. The daily amount of neutral detergent fibr e (NDF) or hemicellulose (HC) degraded was thus 60% higher in the DF g roup (13.6 g NDF day(-1) and 8.3 g HC day(-1)), whereas the quantity o f starch digested was reduced by 50% (9.7 g day(-1)). The rate of pass age 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 particulat e marker (Ce-141) between caecum and rectum was 7 h, whereas for the l iquid marker (Cr-51-EDTA) phase it was 30 h. The passage rates of part icles 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 ).