The respiratory exchange ratio, determined by dividing
VCO2
exhaled by VO2
inhaled, varies according to
energy source (pure carbohydrate R = 1, pure fat R = 0.7).
A study of seven cows at least 2 years old reported a mean
respiratory exchange ratio of 0.91 (±0.05).13 A respiratory
exchange ratio for pre-weaned calves could not be found,
therefore, a value of 0.9 was used in this study. Previous
studies14,15 have used a respiratory exchange ratio of 1.0,
which increases their estimates of alveolar-arterial oxygen
pressure gradient relative to the present study.