## 1 Introduction  
The EU livestock sector is a significant contributor to climatic change, a driver of land-use change, dependent on fossil energy sources, and a significant emitter of greenhouse gas (GHG) emissions [1]. EU member states have significant livestock populations, with more than half of all agricultural holdings (5.7 million) keeping livestock, while the annual value of livestock products is \(\copy\)170 billion. Based on data from 2018, the main livestock populations in the EU consisted of 148 million pigs, 87 million bovine animals, and 98 million sheep and goats [1, 2], while the main outputs of the livestock sector are meat and milk products. Significant data are available on a European level on the production levels, production patterns [2, 3], and financial accounts of livestock [4] held in the EU. However, relatively little information is available on the energy use associated with livestock production in the EU as a whole and for specific livestock categories. In recent years, national and EU policy is increasingly focused on improving environmental sustainability and animal welfare of livestock production, and in order to achieve the goals set out in the Green Deal and the Farm to Fork strategy, livestock rearing, and production will need to transform in the coming decades [5]. For the development and implementation of these goals, a clear understanding of energy use concentrations in the livestock sector in production systems and across production stages is a prerequisite. Eurostat, Faostat, and individual member states provide data on energy use in agriculture, collected through surveys, but not specific livestock sectors [3; 6]. Certain studies look at particular aspects related to energy use and livestock production, including [PERSON] et al. (2016) [7], who investigate the energy use for climate control in livestock housing in Europe, [PERSON] and [PERSON] (2012), who investigated greenhouse gas emissions from the EU livestock sector [8], [PERSON] and [PERSON] (2006), who investigated the energy requirements associated with creating one pound of meat in four European countries [9], [PERSON] et al. (2012) provide an overview of energy consumption in animal production [10], and [PERSON] and [PERSON] (2010) compared the environmental impacts through a number of life-cycle assessments (LCAs) in the livestock sector [11]. In addition, a range of individual studies has been published in recent years, mainly as LCAs, investigating energy use on individual farms in specific agroecological contexts and providing data on the energy embedded in animal feed as well as direct on-farm energy use [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. These include studies that investigated the environmental impacts of beef production systems [12; 20; 23], pig production systems [13; 14; 18; 22], poultry meat and egg production systems [15; 19], and milk production systems [23; 24; 25], as well as smaller livestock production systems, such as sheep and goat [16; 17]. Similarly, there are a number of publications that focus on the production and use of animal feed, which highlights that 60-70% of European farmland is used to produce feed for livestock [10; 26; 27; 28]. Simultaneously, there have been a number of important trends in EU livestock farming in recent decades that affect energy use. These include intensification, whereby livestock farming is increasingly characterized by larger farms and higher livestock densities [29], increased use of breeding techniques (breed substitution, cross-breeding, and within breed selection) [30], increased dependence on imported animal feed, and in recent years, there is a notable shift, driven by both supply and demand factors, towards alternative and more sustainable production techniques based on organic principles and the adoption of fossil-energy-free strategies and technologies (FEFTS) [30; 31; 32; 33; 34; 35]. A review bringing together insights and data from these studies in an accessible manner is necessary.