The effects of different fats and their inclusion level in diets for growing rabbits

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Abstract
Three hundred and sixty male and female Californian ♂ × New Zealand White ♀ growing rabbits were used to study the influence of nine types of fat at 30 or 60 g/kg diet on growth and apparent digestibility. The fats used were: beef tallow (T), pork lard (L), sunflower oil (SO), two by-products from the oil-refining industry, sunflower oleins (O) and soya-bean lecithin (S), and 2: 1 (w/w) mixtures of T + S, L + S, O + S and T + O. All diets, including a diet without added fat, were formulated to a 190 g/kg acid-detergent fibre (ADF) level and to a 100 kJ digestible energy per g digestible protein ratio.As O level in the diet increased, growth was significantly impaired (P < 0·001) but the other fats had no significant effect on this variable (P > 0·05). A maximum oleins concentration in the diet of 10 g/kg is suggested. Excluding diets with more than 10 g oleins per kg, a significant improvement in food conversion ratio was recorded for diets containing 60 g added fat per kg (P < 0·05). This improvement was related not only to a higher gross energy concentration of added-fat diets but also to a significantly (P < 0·001) higher energy digestibility (0·653 v. 0·602 for 60 g/kg added-fat diets and control diet respectively). Fat addition both at 60 and 30 g/kg also improved significantly (P < 0·001) dry matter, organic matter, crude protein and ether extract (EED) digestibilities. As a result, the use of ether extract in addition to ADF for estimating the energy value of diets including added fat, is proposed.An increase in the degree of unsaturation of dietary ether extract increased significantly EED (P < 0·001), but did not affect other variables studied.