CONTINUOUS RESPIRATION RATE MEASUREMENT OF HEAT-STRESSED DAIRY COWS AND RELATION TO ENVIRONMENT, BODY TEMPERATURE, AND LYING TIME

This study uses a continuously sampling sensor to document the respiration rate dynamics of lactating dairy cows under conditions of heat stress. Previously available respiration rate data on lactating dairy cows had primarily been generated by manually counting flank movements at discrete points in time, typically several times per day. Continuous measurements provide much higher-resolution data over time. The primary objective of this study was to analyze these continuous respiration rate measurements in relation to ambient conditions, body temperature, lying time, and time of day. Better understanding continuous responses to heat stress may help synchronize cooling system operation to the cows' need for heat stress relief. For 19 days during a summer season in Wisconsin, eight lactating Holstein cows were equipped with sensors designed to detect the abdominal expansion associated with breathing. An algorithm was developed to derive respiration rate from each sensor's signal. To validate the accuracy of the sensor and algorithms, measurements from the sensor were compared to respiration rate measurements taken via visual observation. Overall, variation in continuously measured respiration rate corresponded to changes in temperature-humidity index (THI) and body temperature. However, respiration rate and body temperature also remained elevated at night despite decreasing THI.