Twenty Finn-Ossimi crossbred male lambs with an average live body weight (14.50 Kg) were randomly assigned into five nutritional groups (each of 4 animals) to receive one of five complete mixed rations containing different percentages of dried bakery by-products (DBP) instead of ground yellow corn as unconventional energetic source. Experimental animals were allotted to one of the following rations in a fattening trial for 124 days; R₁ : yellow corn 50% and 0 % bakery by-products (control ration), R₂ : yellow corn 37.5 % and 12.5% DBP, R₃ : yellow corn 25% and 25% DBP, R₄ : yellow corn 12.5% and 37.5% DBP and R₅ : yellow corn 0% and 50% DBP. A digestibility and nitrogen balance trial were conducted to evaluate the nutritive values of the experimental rations. The effects of these rations on males fattening performance, rumen fluid parameters and economic efficiency were also investigated. Results obtained showed that:   1- Unconventional energetic sources showed higher (P<0.05) effect on most of digestibilities coefficients of nutrients. 2- No significant differences in dry matter intake were observed, however, R₃ recorded the higher intake value (1250 g/h/d) followed by R2 (1190 g/h/d), respectively. 3- R₅ (100 % DBP substitute) showed higher (P<0.05) TDN % and DCP % values followed by R₃ and R₄, respectively. 4- Dried bakery by-products indicated similar positive effects on improving live body weight gain of the experimental animals, and without significant differences among them. 5- Ruminal pH, NH3-N and TVFA's concentration had in general the normal distribution curve, since they increased at 3 hrs after feeding then decreased at 6 hrs later. 6- Dried bakery by products showed (P<0.05) effects on pH, NH₃-N and TVFA᾿s concentrations in ruminal fluid. However, the control ration in general showed lower NH₃-N and TVFA᾿s concentrations in comparison with the other experimental rations. On the contrary, the control ration recorded relatively higher pH value in compare with the other tested rations.    7- R₄, (37.5 % DBP) was the most efficient feed utilization group among the different DBP groups, while R₅, (50 % DBP) was the most economic one. 8- On the contrary, the control group was the most efficient feed utilization group in different feed terms.