Nutritional value of rapeseed expeller cake for broilers: effect of dry extrusion

The effect of extrusion, applied in the production of cold-pressed rapeseed cake on its nutritional value for broilers was evaluated. Two experiments were performed on 55 female broiler chickens, kept individually and allocated to 2 groups of 14 birds (growth trial) or to 3 groups of 9 chickens (digestibility trial). Rapeseed cakes pressed once (RC) or extruded and pressed again (RCE) were mixed in a 6:4 proportion with a basal diet and used in a balance trial with 3-week-old chickens. Furthermore, they were included into wheat-soyabean meal diets at a level of 100 or 150 g/kg and fed during 1-3 and 4-6 weeks of age, respectively, in a growth trial. Due to extrusion and additional pressing, the amount of crude fat decreased from 17.4% in RC to 10% in REC, fat digestibility increased from 83 to 91% (P < 0.0 1), protein digestibility decreased from 79 to 76% (P < 0.01), and the metabolizable energy value decreased from 13.8 to 11.4 MJ/kg DM (P < 0.01). Broilers ate more of the REC diet compared with the RC diet and their final body weight gain was higher (2.61 vs 2.39 kg; P < 0.05). This, as well as a lower relative mass of the liver (P < 0.05) and kidneys (P < 0.01) and a slightly lower mass of thyroids, indicates that extrusion resulted in partial inactivation of the antinutritional factors present in rape seeds.