Application of the Fick principle to the continuous measurement of energy expenditure in pigs

Abstract

The paper reviews the current methods available for the measurement of heat exchange in pigs. The cost of construction of automated open-circuit respiration chambers, in association with climate-controlled facilites, has restricted continuous measurement of energy expenditure in pigs to a small number of laboratories around the world. Ventilated hoods and face mask techniques are not viable alternatives because of difficulties in maintaining a uniform environment around the animal and restriction of food intake. Indirect techniques, including carbon dioxide (CO2) entry rate and doubly-labelled water are only applicable when other technique are not available because of the errors involved when energy expenditure is based on CO2 production alone. An alternative procedure is described for the measurement of energy expenditure in the growing pig. Whole-body oxygen (O2) consumption is calculated from the product of cardiac output and the arteriovenous difference in blood O2 concentration across the lungs (Fick principle). Oxygen consumption recorded with the new procedure was compared with the ventilated hood and CO2 entry-rate techniques, and used to examine the heat exchange of growing pigs maintained at high ambient temperatures