The study was carried out for determine the amount of input- output energy used and indices of energy and economic of fattening farms under different farm sizes in Qazvin city of Iran. For this purpose the data were collected from 30 fattening farms. The surveyed farms were classified into three groups of small (less than 50 heads), medium (50 to 150 heads) and large farms (more than 150 heads).The total average energy input of 24003 MJ calf -1 was required for fattening farm. The share of feed by 75% of the total energy inputs was the highest energy input. This was followed by fossil fuels (16%) and young calf (4%), respectively. The energy use efficiency, energy productivity, Specific energy, and net energy were found as 0.009 (kg MJ-1), 114.8 (MJ kg-1) and -20553(MJ calf-1), respectively. According to the study results, the contribution of indirect energy was higher than that of direct energy; also the share of renewable energy was more than that of non-renewable energy. Economic analysis showed that total average cost of production was 909.8 ($ calf-1). The benefit-cost ratio and productivity were 1.1 and 0.22 (kg $-1), respectively. The results showed that medium farms in terms of economic and energy indexes lower position than the small and large farms. So, they should change their scale to achieve higher efficiency.
