Technical note: comparison of techniques for measurement of oxygen uptake by cattle

The objective of this study was to compare techniques for measuring whole-body O2 uptake of steers. Oxygen uptake provides a basis for evaluating metabolic energy expenditure. We measured O2 uptake as the product of the difference in O2 contents of incoming and exhaust air times air flow through a respiration calorimeter (head box). Additionally, we used catheters and thermistors placed into the blood vessels near the heart to measure cardiac output and whole-body O2 uptake. The cardiac output measurement system used thermodilution to measure the blood flow rate through the pulmonary artery. Catheters placed in the pulmonary artery and in the aorta provided respective samples of oxygen-depleted and oxygen-enriched blood. The product of blood flow rate times blood oxygenation by the lungs provided the basis for calculating total O2 uptake. Four sets of simultaneous measurements with the two techniques were made on eight steers weighing from 272 to 528 kg. Oxygen uptake was not different (P > .20) for the two techniques. Overall (mean +/- SEM) O2 uptake measured by cardiac output (117.2 +/- 7.0 L/h) was 97 +/- 3% of O2 uptake measured by respiration calorimetry.