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

The effects of roasting of lupins or soybeans were evaluated for chemical composition and in situ rumen degradability. Sweet white lupins (Lupinus albus) and a high protein variety of soybeans, AC Proteus (HPSB), were roasted in an electric roaster at a temperature of 300°C with a residence time of 1, 2, 3, or 4 min. Raw and roasted samples were analysed for total nitrogen, acid detergent insoluble nitrogen (ADIN) and protease insoluble nitrogen (PIN), and available rumen by-pass protein (RBP) was determined. In situ degradability of dry matter (DM) and nitrogen (N) was determined using Dacron bags in the rumen of three ruminally cannulated dry cows. Soybean meal (SBM) served as a control treatment. N content of lupins and HPSB was not affected by roasting. Heat treatment increased linearly (P < 0.02) the PIN content of lupins and HPSB. ADIN content of lupins and HPSB significantly increased with increasing roasting time from 1 to 4 min. Available RBP increased more in roasted HPSB than in roasted lupins with increasing roasting time. SBM had lower available RBP than roasted lupins or HPSB. Roasting significantly (P < 0.01) reduced effective degradation of DM and N in roasted lupins and HPSB at a calculated outflow rate in the rumen of 0.06 h−1. The effective degradation of N of HPSB or lupins at 4 min roasting was 10 percentage units lower than SBM. It can be concluded that roasting of lupins or soybeans is a useful tool to increase available rumen by-pass protein and to reduce the effective degradation of N in the rumen of dairy cows.