Accuracy and validation of a radar-based automatic local position measurement system for tracking dairy cows in free-stall barns

A local position measurement system based on radar technology was set-up in a dairy cow free-stall barn. This system could potentially track up to 16,000 individual objects at a frequency of 300 position estimates/s. We describe the general steps for achieving positioning estimates and the transponder developed to be suitable for dairy cows. Measurements at fixed positions and data of dynamic circular measurements are provided, showing that estimates of the location of a transponder were within ≤0.5 m, regardless of whether it was moving or not. Such accurate position information can be used to track cows and to record their travel paths and their use of different areas of the barn. In addition, we tested the system's suitability for monitoring and quantifying social interactions. Though displacements of one cow by another seemed to result in characteristic patterns of changes in the relative distance between the two cows, most of the displacements did not follow this pattern closely enough to allow the automatic detection of displacements. By contrast, we show that the proximity between two cows recorded automatically with the positioning measurement system correlated well with the proximity recorded by direct observation of the cows, and provided a more detailed and exact record over the same period of time. There were no indications that wearing the transponder restricted the behaviour of the cows. In conclusion, the results of our evaluation suggest that the radar-based position measurement system is a useful tool for simultaneously recording the positions of all animals in large dairy-cow herds with great accuracy.