Protein and energy utilisation in rats of diets based on lupin seed ( Lupinus albus var. multolupa)

Abstract

Forty-two 3-week-old Wistar rats were given 3 diets based on lupin seed, autoclaved or not (Diets ALS and LS, respectively) and on soya bean meal (Diet SBM). Energy and N balances were determined and a 24-h respiration experiment performed to measure heat production. Average feed intake and live-weight gain were higher for the SBM diet than for Diets LS and ALS ( P < 0.001). Heat treatment of lupin seed had no significant effect on feed intake or live-weight gain. The protein quality of the SBM diet was significantly superior to that of Diets LS and ALS (true digestibility was 84.8, 81.9 and 80.6 and biological value 60.3, 39.2 and 52.1, for diets SBM, LS and ALS, respectively). The heat treatment of lupin seed did not affect either apparent protein digestibility or true digestibility, but improved N retention ( P < 0.001). The digestible and metabolizable energy of the SBM diet, as well as total energy retention, were higher than those of Diets LS and ALS. The heat treatment caused a significant small decline ( P < 0.05) in both digestibility and metabolizability of energy and a slight increase in energy gain. It is concluded that the biological value of the protein of Lupinus albus var. multolupa is low when compared with that of soya bean. The lower digestive and metabolic utilisation of lupin-seed protein impairs the energy utilisation of diets based on lupin seed. The heat treatment has a beneficial effect on the protein quality of lupin seed. However, it does not clearly improve energy retention.