Raw or roasted lupin supplementation of grass silage diets for beef steers

Lupins were roasted in a flame roaster with an exit temperature of 105 degrees C. The effect of heating on protein solubility and rumen degradability of lupin were evaluated by chemical and Dacron bag procedures. Solubility of nitrogen in buffer was reduced from 69.8% in raw lupin to 35.8% in roasted lupin. Effective degradability of crude protein (CP) and rate of CP degradation predicted by the Dacron bag procedure were lower for roasted lupin (82.3% and 9.2%/h, respectively) than for raw lupin (86.7% and 11.9%/h, respectively). Heat damage measured by acid detergent insoluble N did not differ between raw (3.31% of total N) and roasted lupin (3.46% of total N). 28 Charolais cross steers, 235+or-35 kg, were fed on grass silage only or silage plus supplements containing raw lupin (RL), roasted lupin (ROL) or soyabean meal (SBM) to supply CP at 6.5% of silage DM intake. When steers reached 330 kg liveweight they were given a finishing diet of chopped hay, barley and protein supplements at a rate of 4.5% of barley DMI. In the growing phase, steers fed on RL, ROL or SBM had higher (P<0.05) daily gain than steers fed on silage alone. Steers given SBM had significantly higher daily gain than RL, and steers given ROL had intermediate gains. Daily gain of steers fed on raw and roasted lupin were not significantly different. Silage DMI was significantly lower for diets supplemented with RL and ROL compared with silage alone. In the finishing phase, there were no significant differences in daily gain, carcass weight, dressing percentage, loin eye area or DMI among diets. It is concluded that heat treatment of lupins decreased solubility and rumen degradability of CP, and growth performance of beef steers fed on ROL was similar to that of steers fed on SBM..