The nutritive value of full-fat and defatted Australian rice bran. II. Growth studies with chickens, rats and pigs

Abstract

Growing chickens, rats and pigs were fed on a series of mixed diets containing up to 500 g kg −1 full-fat (FFRB) or defatted (DFRB) rice bran from different harvest years and two regions of Australia. Bran from the 1981 harvest gave reduced growth with young chickens and for birds 4–7 weeks of age in two experiments (1 and 5) but the depression was not consistent. ‘Starbonnet’ FFRB, from northern Queensland, when given at 400 g kg −1 gave much better growth than DFRB from southern N.S.W. Pelleting of DFRB diets for chickens had no effect other than to increase feed intake marginally (Experiment 2). Fibre per se was not the principal constraint to performance of birds fed on mixed diets containing rice bran, since wheat bran with higher neutral detergent fibre (NDF) consistently gave better growth when used at similar levels to rice bran. In general, up to 200 g kg −1 rice bran produced few ill-effects, but there was a linear decline in growth (0.51 g per day) and feed intake (0.76 g per day) for each 10 g kg −1 increment in dietary rice bran above 200 g kg −1 inclusion when given to growing chickens between 3 and 7 weeks of age (Experiment 6). There was no effect on chick growth that could be attributed to rice-bran lipid and the ‘growth-depressing factor’ in the 1981 rice bran could not be extracted with aqueous NaCl solution (Experiment 2). In contrast, there was little effect on the growth of rats or pigs for any of the rice brans at up to the maximum level used (300 g kg −1). The time taken for pigs to grow from 19 to 45 kg was actually less for those fed on diets containing 200 and 300 g kg −1 DFRB than for those fed on the commercial grower diet. It appeared from these experiments that about 200 g kg −1 DFRB may be approaching maximum inclusion level for rats and pigs.