Effect of dietary type and level of fibre on rabbit carcass yield and its microbiological characteristics

The aim of this trial was to study the effect of level and type of fibre during the last week of the fattening period on carcass characteristics. A total of 6602 rabbits (New Zealand×Californian) were divided in three groups and fed with three different diets: HFBP diet (39.6% NDF, 10% beet pulp), HFS diet (39.4% NDF, 8% straw) and LFS diet (37.2% NDF, 4% straw). Feed intake was measured collectively by weighing the feed consumed during the whole experimental period. Thirty two cages were assigned to each replicate that housed around 300 animals, resulting in 7, 7 and 6 replicates for HFBP, HFS and LFS, respectivley. Twenty eight animals per diet, except for the LFS diet with 24 animals, were selected at random to determine the individual carcass yield and the weight of anatomical parts of the digestive tract. Samples of caecal content, the Longissimus dorsi, and Biceps femoris were taken (12 or 14 rabbits per treatment) to determine microbiological counts. The evolution of bacteriological count on the carcass was measured on days 1, 7 and 11 after slaughter. Temperature and pH in Biceps femoris were measured 24h post mortem (12 or 14 rabbits per treatment). Animals fed with the lowest dietary fibre content (LFS) had higher carcass yield (2.7%; P=0.005) and lower bacteriological counts on the carcass (P<0.05) than animals fed HFS or HFBP diets. The type of fibre (beet pulp or straw) did not affect carcass yield but the temperature was higher (0.63°C; P=0.016) and the Enterobacteriaceae and coliform counts were higher in the muscles of the animals fed the HFS diet (P<0.05). A gradual increase with time in storage at 4°C was observed in the microorganism content of the carcass. The highest values were reached at last day of measurement at 11days after slaughter (P<0.001), especially for coagulase-positive Staphylococci in animals fed HFS diet. From these results, it may be concluded that a decrease of dietary fibre (from 39 to 37% NDF) when insoluble fibrous sources (straw) are included, enhances the carcass yield and the carcass microbiological quality. For the same level of fibre, the inclusion of a moderate amount of beet pulp, improved the microbiological characteristics without impairment of carcass yield.