Protein replacement by digestible fibre in the diet of growing rabbits: 2-Impact on performances, digestive health and nitrogen output

The fattening performances, nitrogen excretion and health status of growing rabbits were studied in response to a linear reduction of the digestible fibre (DgF = water-insoluble pectins + hemicelluloses) to crude protein ratio (DFP) in four diets (from 1.01 to 1.55). As the crude protein level was reduced from 17.7% to 13.9% (in diets DFP1–DFP4), the DgF level was increased from 18.5% to 22.1%, without changes to poorly-digestible fibre levels (ADF = 19%). A total of 644 rabbits per diet were used in a multi-site study (n = 6). Between weaning (28d–37d according to sites) and 49d of age, reduction of the DFP ratio led to a linear decrease in weight gain (−4 g/d between DFP1 and DFP4, P<0.001), associated with a reduced feed intake (−5.7% between DFP1 and DFP4). However, for the whole fattening period, growth and intake did not differ significantly among the diets. Over the whole fattening period (35d–70d old), the mean faecal nitrogen output was of 1 g/N per day and per rabbit, and remained similar for the four diets, while the urinary N output was reduced by 55% between DFP1 and DFP4 (P<0.001). Accordingly, the total N output per rabbit was of 82.4 g, 75.5 g, 63.2 g and 57.4 g (P<0.001) in animals fed with DFP1–DFP4 diets, respectively. The nitrogen output per kg of live weight of rabbit produced was 52.0 g, 47.9 g, 40.7 g and 36.9 g for DFP1–DFP4, respectively.At the same time, an increase of the DFP ratio of over 1.3 (CP<16% and DgF > 20%) reduced the mortality by diarrhoea for the two highest DFP ratios when compared to the two lowest ratios (5.2% vs. 7.8%, P<0.05), and led to a 40% reduction of the health risk index between weaning and slaughtering (20.0% vs. 12.6% for DFP1 and DFP4, respectively, P<0.01). A significant reduction of mortality from rabbit epizootic enteropathy (3 sites) was also observed when the DFP ratio was increased to over 1.3. A reduction of the protein level in favour of a higher digestible-fibre level is therefore a useful feeding strategy which improves the resistance of the growing rabbit to enteropathy, without major impairment of performances, and with a reduced nitrogen output.