This study was conducted to determine the chemical composition and rumen degradability characteristics of modified dried vinasse (ProMass) originating from bakers yeast production and to investigate its effects on steer performance, carcass characteristics and some blood parameters. This additive compound with an elevated metabolizable energy (2 800 kcal/g) contained a marked proportion of crude proteins which were remarkably rich in glutamic acid. The degradation of dry matter and organic matter measured in rumens from 4 crossed sheep was very high (about 900 g/kg) during the first 4 hours and the ProMass crude protein was markedly soluble. Forty-five steers were randomly allotted in 3 equal groups according to the mixed diet regimen (concentrates plus forage): concentrates supplemented with 40 g/kg or 80 g/kg ProMass were distributed to assay groups for 24 weeks whereas one group was not supplemented and served as negative control. Growth performance and food efficiency was slightly increased but not significantly in supplemented steers and faecal moisture and serum biochemical profiles (urea, protein and cholesterol concentrations and AST, ALT and ALP activities) were unchanged compared to controls. ProMass supplementation has induced significant reductions of the heart and pelvic fat weights whereas the dressing percentages and the other carcass characteristics remained unaffected. These results showed that ProMass supplies highly soluble proteins, can be included in the steer ration up to 80 g/kg without adverse effects and would promote fat utilization.