## 1 Introduction
In this context, the goal of this paper is to provide a review of energy use in the EU livestock sector by bringing together data from a range of studies. The rest of this section provides a brief description of a conventional livestock system in the EU (specific systems for specific livestock categories are discussed in more detail in the Results section), Section 2 presents the methodology for this review, Section 3 presents the main results from our review, and Section 4 provides a wider discussion. Livestock systems and their energy use in the EU show significant variation and are affected by a variety of factors, including geography, production systems, and agroecological zones [7; 9]. There are, however, a number of important generalizations regarding energy use concentrations, which are described in more detail per livestock category in the Results section. In most production systems and livestock categories, animal feed is the main energy-consuming input [36; 37]. Within the EU, about a third of total manufactured animal feed is compound feed; other ingredients are artificial forages (approximately 50%) and direct-fed raw materials (approximately 20%). In addition, a significant share of feed comes from pasture, estimated to be around 940 million tonnes [38]. According to the EU, 77% of total feed consumption is produced domestically; feed production accounts for around 60% of total wheat, maize, and barley consumption. Despite this, the EU livestock sector is dependent on imported protein sources for livestock feed. It is estimated that the EU has a deficit of about 70% of high-protein materials, of which 87% is met by imported soybean and soymeal [39]. The EU imports 18.5 million tonnes of soybean meal every year, of which 95% goes towards feeding animals [40]. Energy inputs in the production of animal feed are dominated by the production of fodder crops and the associated indirect energy inputs, including fertilizers, pesticides, seeds, and feed supplements [8]. Many existing studies provide figures on the energy use associated with the production of animal feed; these, however, show significant variation depending on origin, raw material use, and livestock system [27]. The production, processing, and transportation of these feeds require a significant amount of energy inputs, which are mostly dependent on fossil sources, and represent a large proportion of the total energy consumed in livestock production. From the data covered in this article, the proportion of feed (concentrates, conserved forage, or grazing) makes up more than 50%, and in many cases 75% or more, of the total energy consumption within livestock sectors. In most systems, livestock is kept in animal housing, but significant variation is reported in terms of energy use depending on the structures used, the agroclimatic conditions, and the types of livestock used [7]. Generally, these systems offer some sort of climatic control of the indoor spaces, and the main energy-consuming categories are heating, cooling, ventilation, lighting, and a range of other devices [7]. In dairy systems, specifically, significant energy consumption is allocated to milking processes [24; 41]. Manure management occurs in a variety of forms depending on the structure of the farm. Manure is generally collected and stored for a period of time in specific storage tanks that can be located underneath or close to the housing system. Various methods exist for moving the manure, such as via conveyor belts, through slated floors, or tractors. During the storage stage, or later, the manure is treated and most usually applied to land at a later stage [41; 42].