Reproducibility of pulmonary mechanics measurements in dairy cattle.

The reproducibility of pulmonary mechanics measurements in dairy cattle was examined using two study designs. In design A measurements were made with six cows on two days, and in design B measurements were made with four cows on six days. The mean coefficients of variation for within-day measurements for individuals ranged from 9.2 to 25.9% indicating considerable within-day variability. In design A there were no significant differences between days (P less than 0.05) for any measured variable for the group, but there were often significant differences between the two days for individuals. In design B there were significant cow-day interactions for all variables, again indicating significant differences between days for individuals. There were significant differences between days for the group for respiratory rate, and duration of inspiration and expiration. Both the interactions and differences between days appeared to be random. The high variability and limited reproducibility of pulmonary mechanics measurements, particularly in individual animals, indicate the need for caution in the interpretation of pulmonary mechanics measurements in dairy cattle.