NITROGEN UTILIZATION BY LAMBS FED PURIFIED RATIONS CONTAINING UREA, GELATIN, CASEIN, BLOOD FIBRIN, AND SOYBEAN PROTEIN1

It is often assumed that ruminants utilize different proteins with equal efficiency regardless of their quality. Johnson and co-workers ( '42, '44) presented evidence from their own in vestigations and a literature review suggesting that all crude proteins fed at the level of 10 to 12 % have biological values approximating 60 for ruminants. They therefore assumed that bacterial protein has a biological value of 60 for sheep and that most feed nitrogen is converted into bacterial pro tein. In contrast to the findings of Johnson et al. ('42, '44), sev eral workers have reported biological values greater than 60 and significant variations in the biological values of different nitrogenous supplements when fed to sheep. Lofgreen et al. ( '47) supplemented a timothy hay and corn ration with urea, urea plus methionine, linseed oil meal, and whole egg protein. This ration contained 10 % of crude protein, 40 % of which was supplied by the individual supplement. Biological values of 71, 74, 76 and 80 were obtained for rations containing urea, urea plus methionine, linseed oil meal and whole egg pro teins respectively. Williams and Moir ('51) have confirmed and extended the work of Lofgreen et al. Supplements o