In this study, data envelopment analysis was employed for determined the energy efficiency of fattening farms in order to separate efficient and inefficient ranchers and to calculate the wasteful uses of energy. Also, the effect of energy optimization on greenhouse gas emissions was investigated and the total amount of greenhouse gas emissions based on present energy consumption was compared with optimum energy consumption ones. The results indicated that out of the total number of fattening farms the share of efficient and inefficient units were 43.33% and 56.67% based on constant returns to scale model, respectively. Also, the results revealed the average of technical, pure technical and scale efficiencies of orchardists were 0.937, 0.953 and 0.983, respectively. The total energy consumption and optimum energy required were calculated as 24,003 and 21,931 (MJ calf(-1)), respectively. Energy saving target ratio for fattening farms was calculated as 8.63%. Also, feed intake had the highest share (53%) from total saving energy, followed by fossil fuels (31%). The total greenhouse gas emissions was assessed as 1176 (kg CO2 (eq.) calf(-1) 6 months(-1)) in fattening farms that value of greenhouse gas emissions can be reduced to 1073 (kg CO2 eq. calf(-1) 6 months(-1)) with optimum energy consumption. (C) 2016 Elsevier Ltd. All rights reserved.