[en] All feasible methods for determining the whole body metabolism of draught animals are indirect and most involve measuring gaseous exchange. The relationship between gaseous exchange and energy metabolism is discussed and the open circuit system described. However, in its classic form it can be applied to draught animals only when they are resting in a respiration chamber or at work on a treadmill or circular race. Three portable devices for measuring the oxygen consumption of animals working in fields are described. All involve the use of airtight face mask so that total respiratory volume can be measured and samples of inspired and expired air taken for analysis. Although all three devices work well in a technical sense, users often experience difficulty in getting experimental animals to behave normally when wearing the face masks and the measuring systems can become inaccurate if the animals start to pant. The theory and applicability of two tracer methods are discussed. Labelled carbon methods are not very accurate and involve continuous infusion of label. The double and triple labelled water methods may find application for measurements over one or two weeks now that several of the objections to the use of these methods on large ruminants have been met. However, both types of tracer method measure only CO₂ output, from which energy consumption has to be inferred, and the latter method is very expensive. Two other methods involve counting the number of heart beats and measuring the type and amount of physical activity of the animal. Both methods rely heavily on data from laboratory studies to link these parameters to energy expenditure. The validity of these methods and the techniques for collecting the relevant data from the animals are briefly discussed. 41 refs, 7 figs, 3 tabs