TECHNICAL NOTE - COMPARISON OF TECHNIQUES FOR MEASUREMENT OF OXYGEN-UPTAKE BY CATTLE

The objective of this study was to compare techniques for measuring wh ole-body O2 uptake of steers. Oxygen uptake provides a basis for evalu ating metabolic energy expenditure. We measured O2 uptake as the produ ct of the difference in O2 contents of incoming and exhaust air times air flow through a respiration calorimeter (head box). Additionally, w e used catheters and thermistors placed into the blood vessels near th e heart to measure cardiac output and whole-body O2 uptake. The cardia c output measurement system used thermodilution to measure the blood f low rate through the pulmonary artery. Catheters placed in the pulmona ry artery and in the aorta provided respective samples of oxygen-deple ted and oxygen-enriched blood. The product of blood flow rate times bl ood oxygenation by the lungs provided the basis for calculating total O2 uptake. Four sets of simultaneous measurements with the two techniq ues were made on eight steers weighing from 272 to 528 kg. Oxygen upta ke was not different (P > .20) for the two techniques. Overall (mean /- SEM) 02 uptake measured by cardiac output (1 17.2 +/- 7.0 L/h) was 97 +/- 3% Of 02 uptake measured by respiration calorimetry.