ABSTRACT. In a completely randomized experimental design with two replicates, the impact of iso-energetic supplements with different protein levels on body and wool growth was studied in eighty crossbreed (Merino Dohne × Corriedale) castrated male lambs (24.5 ± 4.4 kg of body weight, BW, 4 months of age) in summer (103 days) for three years. Animals were randomly allotted to four treatments (n = 20). All lambs grazed native pastures (NP) and animals in three treatments were daily supplemented (2% BW) with an iso-energetic supplement of different CP levels:control (CON, non supplemented), 12% CP (12CP), 16% CP (16CP) and 20% CP (20CP). Supplemented lambs had higher final BW (36.0, 36.4 and 37.7 kg for 12, 16 and 20CP, respectively) than CON lambs (28.9 kg) (P