Abstract: The industrial production of ethanol from cassava produces a large amount of waste. The residual nutrients in this by-product are enough to supplement ruminant animal feeding. Therefore, the objective of this study was to study the effect of yeast fermented ethanol waste (FEW) on feed efficiency and dairy cow performance. Twelve lactating Holstein Friesian cows were assigned to four levels of FEW 0, 25, 35 and 45% of DM in total mixed ration (TMR) diet with fresh ruzi grass (Brachiaria ruziziensis) as the roughage source. Dry matter intake (DMI) and body weight had increased when fed up to 25% of FEW (14.2, 15.4, 11.4 and 7.8 kg/d and 23.7, 6.2, -17.8 and -40.6 kg, respectively; p<0.01). While digestibility of DM, CP, tended to increase, there were no significant difference (p>0.05) in fat, NDF and ADF digestibility. Milk production was higher in animals fed 0 and 25% FEW of TMR diets compared to 35 and 45% (10.8, 11.1, 9.9 and 8.1 kg/d, respectively; p<0.05), while milk composition was not affected (p>0.05). There were no effects on ruminal pH and concentrations of ruminal NH3-N, acetate (C2), propionate (C3), butyrate (C4) and the C2:C3 ratio (p>0.05). Neither were blood glucose and blood urea nitrogen affected (P>0.05). However, total volatile fatty acids (VFA) were reduced with increasing levels of FEW (110.9, 100.9, 105.8 and 94.0 mM/l, respectively; p<0.05). Therefore, it can be concluded that FEW up to 25% of DM can be used in TMR diets for dairy cow feeding.