Use of unmanned aerial vehicles to study cattle heat stress

Heat stress in cattle is a growing problem for the North American cattle industry. Heat stress negatively affects production as it reduces foraging, growth, metabolic efficiency, and may increase mortality rates. Heat stress also negatively affects animal welfare and consumers are increasingly wanting their products sourced from producers that foster good animal welfare. Climate change models predict that average summer temperatures and the frequency and magnitude of heat waves will increase. Given the worsening problem of heat stress, the industry needs to develop and adopt best practices to mitigate losses in production. In principle, increasing heat tolerance may be an effective strategy but measuring heat tolerance is challenging, especially in large-scale studies. Monitoring physiological indicators of heat stress requires invasive devices that are reliable but may be cost prohibitive and logistically challenging. Monitoring behavioral indicators may be practical but still are time- and labor-intensive for large-scale studies. Consumer-grade unmanned aerial vehicles (UAVs) have the potential to be practical and effective tools in studying heat stress behavior. In the second chapter of my thesis, I used thermal-based imagery acquired by a UAV to compare surface temperature between color variants of Black Angus x Canadian Speckle Park cattle. Light-coated animals exhibited lower surface temperatures than dark-coated animals during peak sunlight. This may suggest that light-coated variants are less susceptible to heat stress; however, further research is needed to determine this. In the third chapter of my thesis, I developed a practical and effective method to measure respiration rate using UAVs and Observer XT software. I recorded video at 5-10 meters above steers in feedlot pens and cows on pasture throughout a summer heat wave. Observer XT software was used to analyze behavior from UAV-based video. Respiration rates were determined by quantifying flank movements observable on video. Consistent with similar studies, respiration rate was the highest in black cattle, followed by red cattle, then white cattle in the feedlot. Coat color did not affect respiration rate in cows on pasture; however, temperatures on pasture were lower than in feedlots and the effect of coat color may not manifest until a certain temperature threshold of heat load index (HLI). In conclusion, consumer-grade UAVs seem to be an effective tool for measuring heat stress behavior of cattle in large scale operations. Future research could further improve the efficacy of UAVs with the addition of extra sensors and with the use of automation through machine learning methods. UAV-borne thermal imagers provide limited information and warrant further improvement. It is likely that, in the feedlot, dark-coated cattle are less productive than light-coated cattle during high heat loads but further research is needed to make a direct comparison of productivity. The inclusion of Canadian Speckle Park animals in primarily Black Angus commercial breeding programs has the potential to introduce thermotolerant traits into the popular Angus breed. However, further research is needed to determine if coat color has an effect on heat stress and productivity.