The functional relationship between non-renewable energy use and milk yield in Iran.

Data from a face to face questionnaire survey were conducted to contribute to the development of a method for investigating the relationship between energy inputs and yield of milk production in the Tehran Province of Iran and study on NRE and RE. The results revealed that total non-renewable energy of 9997 MJ cow-1 was expended in a period of 365 days; while fossil fuels and electricity were the main energy consuming inputs. Moreover, in specifying a functional relationship the Cobb–Douglas production function was selected as the best function due to its better performance in statistical significance and expected signs of parameters. It was found that fossil fuels energy contributed to the milk yield significantly; while the use of machinery and electricity were inconsistent. The marginal physical productivity (MPP) was applied to investigate the effect of energy use on milk yield. It was concluded that milk production had more sensitivity on fuels energy; hence an additional use of 1 MJ from the fossil fuels energy would lead to increase in yield by 0.18 kg cow-1. The controlled use of NRE inputs and expansion of applying more renewable energy (RE) sources as an alternative to fossil fuels is recommended.