A Comparison of Ventilated Hood and Respiration Chamber Systems for Measuring the Gas Metabolism in Sheep

Abstract

A series of comparative experiments was carried out to evaluate the accuracy of a simple respiration apparatus equipped with a ventilated hood for measuring the gas metabolism in sheep.
The apparatus consists of three main parts: (1) a ventilated hood attached to a metabolism crate, (2) a set of blowers with a gas meter, which regulates the ventilation rate and the expired air flow, and (3) a gas analyzer unit for determining the concentration of oxygen, carbon dioxide and methane in a mixed air sample of fresh and expired air. Oxygen consumption, carbon dioxide and methane production of sheep were measured by the differences in concentration of each gas between fresh and sampled air multiplied by the ventilation rate.
Accuracy test by burning a measured quantity of methanol in the apparatus revealed that the measured values of oxygen consumption and carbon dioxide production agreed closely with the predicted ones.
In comparison with the measurements of gas metabolism in sheep obtained from the chamber system, the ventilated hood system tended to give somewhat lower values in gas metabolism but there were no significant differences in these and the estimated values of heat production between two systems. The ventilated hood system is found to fullfil satisfactorily the following requisites: (1) the possibility of measuring the gas metabolism in sheep naturally, without any appreciable restricting or distorting effects on the behavior of the animals, (2) the disirability of the system so as to ensure expeditious measurements in responding to the respiratory exchange in animals, and (3) the possibility of continuous measurement for a long-term respiration experiment.
Evidence obtained from the present experiments indicated that this type of apparatus should be useful for measuring the diurnal changes in gas metabolism and for determining energy expenditure in sheep.