The utilization of lupin (Lupinus angustifolius) and faba bean globulins by rats is poorer than of soybean globulins or lactalbumin but the nutritional value of lupin seed meal is lower only than that of lactalbumin.

The effects of dietary sweet lupin (Lupinus angustifolius, Unicrop) seed meal or its insoluble fiber (nonstarch polysaccharides + lignin) on performance, digestibility and nitrogen utilization in growing rats were studied in four experiments. Globulin proteins isolated from lupin, faba bean (Vicia faba L. minor) or soybean (Glycine max) were also incorporated into purified diets as replacements for lactalbumin (control) and the nutritional effects were evaluated. Isocaloric, legume-based diets supplemented with amino acids were used. Final weight gain, gain:feed ratios, nitrogen retention and net protein utilization of the animals fed whole lupin meal-based diets for 10 d were inferior to those of controls. In contrast, adding lupin insoluble fiber to a control diet produced no adverse effects. Ileal starch and apparent nitrogen digestibilities, and fecal digestibility of starch in lupin-fed rats were higher than those of controls, but fecal true nitrogen digestibility was lower. Replacement of lactalbumin with globulin proteins from lupin or faba bean depressed food intake and protein utilization, but only performance was affected by consumption of soybean globulins. Rats consuming lupin or faba bean globulins excreted significantly more nitrogen, particularly as urea through the urine. This did not occur in rats fed soybean globulins. Urea concentration in plasma was higher in rats fed diets containing lupin meal or legume globulins. The concentrations of urea, arginine and ornithine in plasma increased significantly compared with control values after 3 to 9 h of a lupin diet. After 9 h, plasma lysine was also decreased. We concluded that the main reasons for the low nutritional value of sweet lupin seed meal are likely to be related to the chemical structure of the globulin proteins and their adverse effects on growth and nitrogen metabolism, and not to any known antinutritional factor or poor digestibility.