‘Robro’ and ‘Hybro’ broiler strains were fed rations with three levels of energy during different seasons (six periods) to evaluate the effects of these factors on broiler traits. Each unit was replicated in five tiers of batteries for 49 days (length of one period). Total gain was significantly affected by period and strain and their interaction. ‘Hybro’ birds gained more than ‘Robro’. Hot weather reduced gain and feed intake and increased mortality. Birds consumed less feed at the high energy level. Feed efficiency was affected by period but there was no pattern related to temperature. Dressing percentage was higher in 'Hybro' and in cool seasons. The main factors affecting performance are period and strain. Energy at the levels studied did not affect performance. Cooling during bot seasons is suggested; further research in this area is needed.