Evaluation of raw and roasted lupin seeds as protein supplements for lactating cows

Lupin seeds, raw or roasted, were compared with soybean meal as protein supplements for dairy cows by determination of crude protein fractions, rumen fermentation characteristics, digestibility of nutrients, and lactation performance. Roasting increased the estimated undegraded crude protein fraction of lupins from 37.7% to 44.7% compared to that of soybean meal at 36.0%. Acid detergent insoluble nitrogen in roasted lupins did not increase markedly compared to raw lupins, indicating minimal protein damage due to roasting. Isonitrogenous substitution of raw or roasted lupins for soybean meal in lactation diets did not substantially change rumen fermentation characteristics or whole tract digestibility of nutrients. However, cows fed roasted lupins produced more milk than those fed raw lupins. Higher yields of fat, protein and lactose from cows fed roasted versus raw lupins were primarily due to increased milk yield. Milk fat from cows fed lupins had higher concentrations of long-chain fatty acids compared with milk from cows fed soybean meal. Improved lactational performance of cows fed roasted versus raw lupins was probably due to more sustained release of protein in the rumen, increased undegraded protein supply, and increased efficiency of utilization of dietary energy for milk energy output.