Agreement between passive infrared detector measurements and human observations of animal activity

Based on the characteristics of both measurement methods, the correlations between PIR detection and human observation of animal activity were strong, with a Spearman's correlation coefficient of 0.90 (p < 0.001) and a concordance correlation coefficient of 0.86. PIR detection overestimated animal activity by 2.59% as compared to human observation, and the precision of PIR measurements decreased with the increase in the level of activity in the pen. In addition, animal weight affected the quality of measurements, which decreased with the increase in the ratio between kg of live weight and area covered by the sensor. The type of activity affected the precision of PIR detectors, which better detected playing activities, which are more intense than feeding activities. It can be concluded that PIR detector measurements of activity in groups of animals provide a good estimation of the relative activity of the group, which is comparable to visual estimation of relative activity.