The population of the world is growing. In 2000, the world population was 6.1 billion, and it is estimated that there will be an increase to 8.2 billion people by 2030 (Schneider, 2010). The security of the food that will feed this growing population is a significant challenge. Recently, more than 3.7 billion people were faced with malnourishment (Pimentel, 2009). In 2010, it was determined that of these 3.7 billion, 925 million people, mostly in developing countries, were undernourished, and these numbers have been increasing worldwide since 1995 (FAO, 2010). However, agriculture produces enough food to overcome future demands. Poverty and undernourishment of a large part of the population is caused by fundamental problems in the distribution of food and resources (FAO, 2002).
Agriculture plays a role in the improvement of food security worldwide by contributing to the growth of the economy in most developing countries and thereby reducing poverty (Pingali and McCullough, 2010). Livestock farming is an important sector of agriculture that contrib-utes intensively to these aspects of food security. The demand for livestock products is in-creasing. The increase in demand for livestock products is growing more rapidly than the population growth rate (Schneider, 2010). Because of population growth, increasing living standards and shifting demographic parameters (e.g., urbanisation and rising incomes), the demand for animal products has increased (Steinfeld et al., 2006). Global production of milk and meat in 2050 is projected to be more than double the production of 1999 (Steinfeld et al., 2006), an increase that is being called the Livestock Revolution (Devendra, 2002).
At the same time, agriculture is seriously challenged by environmental problems such as the reduction of water quality and farmland quantity due to erosion, developing infrastructures, and extensive grazing (Steinfeld et al., 2006). Increasing debate regarding the impact of ag-riculture on the environment has led to less use of chemical fertilisers and pesticides and more restrictions on greenhouse gas emissions. It is assumed that these restrictions will lead to a decrease in the production yield (Börjesson, 1996). Therefore, to compensate for these restrictions and increase food production, the use of more intensive, mechanised, and pre-cise agricultural systems is unavoidable, which will cause higher energy consumption in food production. However, the depletion of the fossil fuel stocks and increasing oil prices may re-sult in a further decrease in energy consumption.
Energy efficiency improvement is one of the most important aspects in regard to combatting these challenges. Energy efficiency improvements contribute to the reductions of emissions and climate change (Varone and Aebischer, 2001) and are a solution for fuel resource re-strictions. The study of energy flow and energy efficiency will allow us to recognise
bottle-necks and, subsequently, improve the production processes to achieve systems with more energy efficiency.
Energy efficiency first garnered attentions after the oil crisis and resulting increase in oil pric-es in the 1970s (Zuberman, 2009). Primarily, economic and political indicators and later, en-vironmental issues (linked with the consumption of fossil fuels), brought the reliability of pro-duction systems and the dependency on fossil fuels to the forefront. With this goal in mind, Life Cycle Assessment (LCA) models were introduced to assess the life of a production pro-cess. In 1974, after some individual works the International Federation of Institutes for Ad-vanced Studies (IFIAS) in Stockholm tried to standardise energy efficiency investigations so that the results of different studies could be compared (Zuberman, 2009). At the 1992 Inter-national Environment and Development Conference in Rio de Janeiro, new guidelines and indicators were introduced to support the assessment of national and international develop-ment processes in regard to sustainability (UN, 1992). These attempts led to the introduction of several standards and guidelines, such as VDI 4600 in 1997 (revised 2012) and ISO 14041 in 1998 (revised by ISO 14044, 2006). Additionally, several software models have been introduced to help to analyse the systems. Some examples of these models are the KUL-method (Eckert et al., 1999) and REPRO (Hülsbergen, 2003) in Germany, EMA system (Lewis & Bardon, 1998) in Britain, and ESI-method (Sands & Podmore, 2000) in the USA.
Agriculture is one of the three main economic sectors (in addition to industry and services) (Schäfer, 2003) that consume energy resources and emit greenhouse gases (GHG). Scien-tists have investigated and assessed the energy efficiency of agricultural systems. Farming practices (which differ in intensity), region, crop type, and management have been evaluated by energy efficiency indicators. These studies showed a reduction of the energy output input ratio (OIR) in more intensified systems because the increase in the yield was less than the increase in the consumption of non-renewable energy resources, such as fuels and fertilisers (Pimentel et al, 1973; Pimentel et al., 1998; Kuesters and Lammel, 1999).
The energy efficiency of livestock production is lower than that of crop production (Pimentel, 2009). In comparison to crop production, few studies have been conducted on the energy efficiency of livestock farming (Wechselberger, 2000). The number of intensive livestock sys-tems is increasing, and the land and livelihood needs of extensive syssys-tems are crucial chal-lenges of livestock farming (Schneider, 2010). There is insufficient knowledge about the en-ergy efficiency of production technologies in animal husbandry, in addition to little information on how targets and intensity of production may influence energy efficiency.
There is a rapidly increasing demand for dairy products in Iran, as well as in most developing countries. Pastures in Iran are mainly low in quality and sensitive to overgrazing due to the primarily dry climate (Badripour, 2006). Therefore, most feedstuffs used in cattle farming are
produced intensively on farms in competition and rotation with foodstuff production. The use of croplands for the production of feedstuffs or consumption of grains as feedstuff to meet the increasing demand of livestock production is a threat to the sustainability of the food supply in Iranian agriculture.
The aim of this study is to estimate and assess the energy efficiency of dairy cattle farms and feedstuff production farms in common systems that are prevalent in north-western Iran. The most useful indicators in energy efficiency investigation in the production of feedstuffs and also dairy products are the energy intensity (EI) and energy output input ratio (OIR). These indicators are calculated for both milk and meat from dairy cattle farms. The comparison of the energy efficiency of several farms that differ in herd size, cattle breed quality, keeping systems and management makes it possible to determine which systems are more efficient and trace more efficient processes and activities inside these systems.
To preserve a scientific and standard method of investigation and to be able to assess and compare the production processes with other similar studies, the Cumulative Energy De-mand (CED) concept described by VDI guideline 4600 (2012) and the Life Cycle Assessment (LCA) concept specialised by ISO standards 14040 and 14044 (2006) were used. Sensitivity analysis described the uncertainties of the results and identified connotative fields for further investigations.