Effects of roasting of lupins (Lupinus albus) and high protein variety of soybeans (AC Proteus) on chemical composition and in situ dry matter and nitrogen disappearance in dairy cows

Sweet white lupins (Lupinus albus) and a high protein variety of soyabeans, AC Proteus (HPSB), were roasted in an electric roaster at 300 degrees C for 1, 2, 3 or 4 min. Raw and roasted samples were analysed for total nitrogen, acid detergent insoluble N and protease insoluble N, and available rumen by-pass protein (RBP) was determined. In situ degradability of DM and N was determined using Dacron bags in the rumen of 3 ruminally cannulated dry cows. Soyabean meal was used as a control treatment. Roasting did not affect the total N content of lupins (4.9%) and HPSB (7.3%), but increased linearly (P<0.02) the protease insoluble N content of both. As roasting time increased the acid detergent insoluble N content of lupins (4.7, 5.1, 6.7 and 7.9% at 1, 2, 3 and 4 min roasting, respectively) and HPSB (4.9, 6.3, 6.6 and 7.2% at 1, 2, 3 and 4 min roasting, respectively) increased. Available RBP in roasted HPSB increased as roasting time increased (27.6, 33.8, 41.2 and 43.3% at 1, 2, 3 and 4 min roasting, respectively); however, roasting time did not affect RBP of roasted lupins (20.6%). Soyabean meal had a lower RBP percentage than roasted lupins or HPSB. Roasting reduced (P<0.01) effective degradation of DM and N in roasted lupins and HPSB at a calculated outflow rate in the rumen of 0.06 h/day. The effective degradation of N in HPSB or lupins at 4 min roasting was 10% lower than in soyabean meal..