The measurement of draught ruminant energy expenditure in the field

Abstract

The aim of this work was to improve and validate the Oxylog portable oxygen consumption meter for use with draught ruminants, and to test its ability to estimate the energy expenditure of these animals in the field.Few data were available on the energy costs of the various tasks that draught ruminants perform and it was expected that the calorific factors established during laboratory experiments may not necessarily reflect the energy consumption during field work with farmers. This could have important implications in the establishment of the nutritional requirements of draught ruminants.A review of the literature on the various techniques and instruments available for the field measurement of energy consumption was carried out.A new facemask for use with the Oxylog was designed and the Oxylog equipment with this mask was validated against the open circuit gas analysis system available at the Centre for Tropical Veterinary Medicine in Edinburgh. It was found that the Oxylog, on average, overestimated oxygen consumption, as measured by the gas analysis system, by 1.5 %.In the second experiment, carried out with buffaloes and oxen pulling carts on the Unipalma oil-palm plantation in Meta, Colombia, the modified Oxylog system was tested in the field. Technically, the method worked satisfactorily, although the small digital displays on the Oxylog were difficult to read, and the measurements obtained generally agreed with the more established calculation methods of estimating energy consumption. It was concluded that the use of the modified Oxylog was an accurate and reliable method for the estimation of energy expenditure in the field. Insufficient time, however, was available to train the animals to wear the facemask and to accustom them to the experimental procedures, hence, the acceptance of the mask was low. The use of a constant value for the energy cost of walking over various terrains and the difficulty in accurately defining the animals' respiratory quotient, were also thought to have affected the results.In the third experiment, the influence of soil consistency on the energy cost of walking and the efficiency of working in Bunaji (Bos indicus) draught bulls in the sub-humid zone of Nigeria was investigated. These experiments were carried out in collaboration with the International Livestock Centre for Africa. A dataviewer was designed to facilitate data collection. To ensure that the respiratory quotient only varied between 0.8 and 1.0 the animals were fed 3 kg of concentrates, 1 h before the start of the experiments so that they were primarily metabolising carbohydrates. Eight experimental animals were trained over a period of four weeks and the mask acceptance rate was 100 %. The energy cost of walking on the different soils varied from 1.47 J/m/kg to 3.30 J/m/kg. Ploughing doubled or more than doubled the energy cost of walking on the soils investigated. Although the consistency of the soil did not influence the efficiency of doing work, both the speed of walking and work¬ ing, and the distance average draught force were affected. A simple method to estimate the energy cost of walking based on the speed of walking on soils of different consistencies was proposed. It was further established that it would be more efficient to cultivate soils before they became inundated with water, because as they became wetter more time, effort and energy were needed for cultivation per unit area.It was concluded that the modified Oxylog, although its use will be largely restricted to trained animals being investigated by research organisations, is a useful and reliable tool in draught ruminant field calorimetry.