Monitoring heat stress in dairy cows: Part 2 – automation and sensors

Heat stress related production loss, compromised welfare and cattle mortality are global concerns which are increasing in the context of climate change and global warming. To maintain the welfare and performance of livestock, monitoring the effects of climatic extremes is important. Farming systems are becoming increasingly automated and remote/automated monitoring of animals is an ultimate need to overcome the limitations of human observation for continuous characterization of cows situation for farm management and scientific discoveries. Several remote/automated monitoring techniques are under evaluation, and other, have been already validated to monitor cattle behavior and health, including being heat stressed, and are in use in advanced dairy farms all over the world.

The aim of this article is to describe existing sensor-based methods to monitor individual cattle heat stress responses, through behavioral and physiological indicators (panting score and core body temperature), and climatic indices (temperature humidity index, THI and heat load index, HLI). Such technologies can help identify individual or groups of cows, suffering heat stress, as well as find heat-susceptible animals for isolated mitigation strategy through an advanced sensor system.

   

The pressure changes associated with muscle tone, chest movement and exhaled air can be autonomously monitored. Continuously recorded respiration rate, using thin-film pressure sensors and a small, battery-powered microcomputer found a clear change in unshaded and shaded animals. A similar sensor system, with the addition of an algorithm and data filter to remove unreliable signals found that the respiration rate monitored records corresponded to body temperature and ambient thermal conditions (THI). An automated long-term respiration rate monitoring system was developed and validated in dairy cows with high association with flank movement. Micro-electro-mechanical-system (MEMS) based on magnetic sensors provides more accurate breathing signals and greater spatial resolutions with lower measurement errors. This system presents an alternative to existing respiration rate sensors, with some modifications required for cattle in commercial settings.

Biosensors have been developed to log cattle body temperature and account for individual variability in thermoregulatory ability. However, temperature-logging sensors without remote transmission of data limits real-time monitoring. Temperature sensing ear-tags, rumen-reticular boluses, intra-rectal and intra-vaginal devices, and wearable and implantable (micro-chips) devices with remote data transmission ability need further development regarding heat stress prediction models, based on real-time temperature data. Ingestible bio-sensors and radio-frequency identification (RFID) sensors can monitor the internal temperature of cattle with individual identity. Radio telemetric thermo-logger data suggests that monitoring the thermoregulatory responses of cattle requires continuous measurement of body temperature. However, telemetric measurements are still costly and can only operate over short distances, small numbers of animals and for short time durations. Deflected, absorbed, interfered or distorted radio frequency can provide false data in real time data transmission. The radio telemetric measurement of core body temperature, undertaken by implanting a transmitter and data logger in the abdominal cavity of dairy cattle showed the change in core body temperature to be dependent on ambient conditions, and a lag from ambient temperature of 1 to 5 h.

The use of global positioning system (GPS) based technology for monitoring animals outdoors is increasing. Lightweight GPS collar receivers are suitable for monitoring animal position at 5-min intervals. Animal behavior characteristics and pasture utilization can be assessed by importing the GPS data into a geographic information system (GIS). The use of GPS collars with additional temperature and dual axis (2D) motion sensors in intensively managed beef cattle revealed that cows passed inactive time near a watering point when temperature ranges were from 30 to 35 °C and sequentially started grazing when temperature started to decrease. There is potential to continue research in this area for time-sequenced studies of behavioral response to heat stress. Ear tags integrating solar-powered GPS trackers are also commercially available. Neck-mounted GPS based virtual fencing (VF) technologies for cattle are emerging and present a real-time solution for animal monitoring, control of animal movement and even targeted heat amelioration through isolation of susceptible cattle if integrated with additional temperature and motion sensors. Real-time location systems (RTLS) are tracking systems consisting of a fixed receiver or reader that reads location information of an animal wirelessly from small ID tag attached to them, mostly used in indoor conditions or in a specified confined area. The location and movement of an individual animal in the proximity of feed, water and cooling site can be detected and used for developing behavioral indices. The RTLS based location data can be used to develop algorithms to predict eating, drinking, lying and grooming behaviors. Such systems can identify individual animals that are spending more time near water, shade or cooling site and thereby determine its heat susceptibility.

Accelerometers are devices that measure the acceleration of motion of a structure in 2D or 3D space. They work by recording static and dynamic acceleration, using electromechanical sensors. These acceleration data can be converted through effective algorithms to understand the state of an object. Each behavior of an animal has characteristic movement of the body or idleness. Animal static or dynamic movements captured in 3D can be used to classify core behaviors through defined algorithmic transformation. For example, eating, drinking, grazing, rumination, lying/resting, standing, and activity of cattle were detected by accelerometers with good correlations and moderate to high sensitivity specificity, compared with visual observations. Tri axial accelerometers were used to measure the flinch, step and kick response to assess stress and discomfort in dairy cows under pasture-based system. In addition, forward-backward heaving (panting) has been assessed, along with other respiratory dynamics, as a potential indicator of panting for accelerometer-based monitoring of heat stress response in dairy and feedlot beef cattle. Therefore, accelerometer-based cattle monitoring data could enable a multimodal behavior based heat stress prediction/alarm model for early strategic mitigation interventions, and recently, also in managing large scale commercial dairy farms. Ear tag accelerometer sensors are most promising in this regard having been validated under moderate to hot conditions for panting score. However, further work is required to validate such systems during heatwave events, where significantly higher panting scores are recorded. Validated sensor data should be used for determining panting duration upper thresholds, above which mitigation measures for heat stress can be activated. Such monitoring will provide useful actionable insights at the individual animal level allowing potential improvements in cattle welfare in heat stress, health and production issues.

Climatic data can be continuously obtained from on-site weather stations and processed for automated and remote monitoring of thermal conditions. Weather stations with wireless connectivity can relay data into a network accessed virtually from anywhere. Smartphone-based applications using similar protocols have been developed combining current and projected weather information with individual animal information, helping the decision-making process by sending alerts to reduce heat stress. Portable climate data collection devices with Bluetooth connectivity can calculate THI in different microclimatic areas across large-scale farming environments. However, climate data-based assessments are indirect measures of animal response to heat stress and a fixed threshold of chosen indices in these applications may serve farmers for monitoring “herd situation”, but this information can’t be equally applicable for individual cattle.

Computer vision-based video surveillance could be the ultimate off-animal monitoring device in the future. A video cameras (red light video at night) was used to observe physiological and behavioral changes of dairy cattle exposed to summer weather and found that respiration rate, skin temperature and body temperature increased alongside THI. Artificial neural network, fuzzy logic classifier and machine learning based approaches, using animal physiology and climatic variables have been found promising in monitoring animal thermal status under experimental conditions. Considering the speed of technology development, these will very likely be useful under practical conditions in the near future. The size of the recorded data may be an issue for storage and transmission of information.

Development of methods of data compression into less memory-consuming images or videos (or transforming into a different signal) and advanced feature extraction methods from transformed data, preferably from cloud-storage, could be potential future improvements in this space. Capacity building for on-site instant analysis of data may minimize data transmission and storage requirements.

Infrared thermography (IRT) can estimate the body surface temperature of cattle. The IRT images of different body regions were collected to measure body surface temperature patterns and were found to be highly correlated with THI and right flank, left flank and forehead temperatures. In addition, IRT forehead temperature showed also good correlation with rectal temperature. Infrared images were used to measure respiration rate to assess stress and discomfort in cows under pasture-based system. The respiration rate measured by continuous IRT imaging of airflow through the nostrils had good agreement with the live and video recording-based measurements. This result suggests that with further development, IRT could be incorporated for the remote monitoring of cattle heat response. However, IRT imaging and videos require a controlled environment involving additional cattle handling for data recording and sophisticated software for analysis. For example, IRT image-based forehead, dewlap and body surface temperature varied under a similar THI value and also, raw IRT video data were poorly correlated with cattle internal body temperature and thermal status, and could only be used after extensive manipulations.

In conclusion, new and sophisticated “sensing and transmitting” technologies in development these days, will help dairy farmers identify individual or groups of cows, suffering heat stress, and activate heat mitigation means on time and efficiently, as well as find heat-susceptible animals for isolated mitigation treatments.