NUTRITIONAL EVALUATION OF LOW AND HIGH FIBRE FRACTIONS OF RAPESEED MEAL USING CHICKENS AND PIGS

Abstract

Samples of Brassica napus and B. campestris rapeseed meals were separated into fractions low in crude fibre or high in crude fibre using an ’air classifier.’ The original meals contained 15% crude fibre and these levels were reduced to 8 and 10%, respectively, for the ’low fibre’ fractions from the two types of rapeseed meal, and increased to 23% in the ’high fibre’ fractions. There was 42.2 and 40.5% crude protein, respectively, in the original meals, and this was increased to 46.7% and 45.2%, respectively, in the low fibre fractions and reduced to 33% and 37%, respectively, in the high fibre fractions. The above six samples, along with rapeseed meal from the Bronowski cultivar of B. napus and 49% protein soybean meal were assayed for metabolizable energy using 4-wk-old chicks. The classical metabolizable energy values of the B. napus, B. campestris and Bronowski meals were 1.49, 1.66 and 1.71 kcal/g compared to 2.26 kcal/g for the soybean meal. The low fibre fractions from both types of rapeseed had a metabolizable energy value of 2.19 kcal/g, whilst the values for the high fibre fractions were 1.36 and 1.56 kcal/g, respectively, for B. napus and B. campestris. Incorporation of the rapeseed products as protein supplements in isocaloric 17% crude protein broiler diets resulted in similar gains for the three diets containing rapeseed meal and for a control diet containing soybean meal; however, gains were reduced for both the low and high fibre fractions. The poor performance of the birds on the diet containing the low fibre fractions was probably due to the birds having difficulty in consuming the dry powdery diet. A further growth study with 23% protein broiler diets showed that replacing one half or all the supplementary protein from soybean with the rapeseed low fibre fractions reduced weight gain, although in both experiments the rate of gain per unit liveweight over the last week of the experiment was similar for all diets, again suggesting that the birds had difficulty in adjusting to the diet. The digestible energy value of the B. campestris meal for 25-kg barrow pigs was 3.47 kcal/g. The values for the low and high fibre fractions from this meal were 3.67 and 3.39, respectively.