Background Protein feed resources for ruminant animal productions are deficit in Ethiopia. Objectives To evaluate the supplementation effects of dried Dodonaea angustifolia leaves (DDL), dried traditional brewery by‐product locally called atella and their mixtures on nutrient utilization and growth performance of Farta sheep fed natural pasture hay (NPH) as basal diet. Methods Twenty‐five yearling intact male Farta sheep with average initial body weight of 14.53 ± 1.35 kg (mean ± SD) were used for the study. The experimental sheep were allocated into five blocks of five animals based on their initial body weight. The experiment lasted for 90 days of feeding trial followed by 7 days of digestibility trial. The experimental feeds were NPH ad libitum + 100% DDL + 100 g wheat bran (WB; T1), NPH ad libitum + 75% DDL + 25% dried atella + 100 g WB(T2), NPH ad libitum + 50% DDL + 50% deried atella + 100 g WB (T3), NPH ad libitum + 25% DDL +75% dried atella +100 g WB (T4) and NPH ad libitum + 100% dried atella + 100 g WB (T5). Results NPH, DDL and dried atella contained 7.42, 15.39, 21.13% crude protein (CP) and 66, 36, 34% neutral detergent fiber, respectively. Sheep supplemented with increasing level of atella had more dry matter intake (DMI) and crude protein intake (CPI) and the highest of these DMI and CPI were in T5 (868 g/d for dry matter and 113 g/d for CP). This progressive increased CPI from T1 up to T5 was reflected in a significant (p < 0.001) fibers and estimated metabolizable energy intake in the order of T5 > T4 > T3 > T2 > T1. Significant difference (p < 0.001) was recorded on nutrient utilization and the highest was for T5 and lowest for T1. Average daily gain (ADG) and feed conversion efficiency (FCE) were significantly (p < 0.001) increased as the atella inclusion level increased. Sheep in T4 and T5 had the highest ADG and FCE with the order of T5 = T4 > T3 > T2 > T1. ADG was correlated positively and highly significant with nutrients intake and digestibility. Conclusion Atella supplementation better than DDL and then their mixture (T2–T4) supplementation could be recommended in sheep fattening in the study area.

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