The impact of energy supplementation on the performance and carcass characteristics of 24 Aberdeen-Angus * Charolais steers grazing an annual ryegrass ( Lolium multiflorum) and oat ( Avena strigosa [ Avena nuda]) pasture managed in order to avoid constrains to animal performance was evaluated. Treatments were levels of supplementation of 0, 0.4, 0.8 and 1.2% BW with a corn and mineral based supplement. Animals were slaughtered after reaching 4.5 mm of fat cover in the rump (P8) evaluated ultrasonography. No differences were observed in fat deposition, measured in live animals with ultrasound at the end of performance period, and in liveweight gain, which showed average values of 3.9 mm and 1.54 kg/day, respectively. Blood serum levels of urea were linearly decreased and cholesterol linearly increased by energy supplementation, with no differences in the serum levels of glucose and triglycerides. Energy supplementation linearly increased the killing-out proportion and carcass weight gain, but no differences were observed on the rib eye area, slaughter weight and hot carcass weight, which averaged 67.85 cm 2, 438.95 kg and 227.75 kg, respectively. Increasing the levels of supplementation resulted in higher killing-out proportion and higher carcass daily gains, without changes in performance and carcass parameters evaluated.
