Dairy Cow Heat Stress Within Building Microclimates

Lactating dairy cows generate a significant amount of body heat due to their high metabolic rates. Excess heat must be dissipated and a failure to do so leads to heat stress. The ideal ambient temperature for dairy cows ranges between 5 - 25 degree C, but this is affected by breed, feeding level, production, and other individual factors; temperatures as low as 20 degree C may lead to heat stress in some cows. Such conditions are common in the UK during summer, and can even occur in the winter, particularly indoors. Heat stress is already a problem on many UK farms, but predicted increases in average temperature and the frequency and duration of heat waves resulting from climate change, makes the issue even more urgent. Heat stress can result in a range of physiological problems including reduced feed intake and milk yield, and impaired fertility and immune function, all of which negatively affect cow welfare and the economic sustainability of dairy farms.

Cows are known to adapt their behaviour to help cope with high temperatures and humidity: they may increase their intake of cold water, seek shade or areas of increased ventilation, or exhibit other individual and social behavioural responses. Not all cows show obvious physical signs of heat stress and hence monitoring has typically been based on proxy measures such as local weather station temperature and humidity records, or measurements from a few indoor sensors. However, recent research, including by our team, has shown that temperature, humidity, and ventilation within barns have high spatiotemporal variation, and are affected by both building design and usage, as well as external conditions. The presence of these barn 'microclimates' means that cows experience different individual-specific conditions, varying over time and space, that will influence their ability to cope with heat stress (and hence their subsequent physiological and behavioural responses). Social interactions and herd-level responses may also be affected by, and directly affect, the indoor microclimate: we have evidence that cows housed indoors spatially cluster with increasing temperature, a potentially maladaptive response since social clustering further increases localised temperatures.

In this project we will use location tracking technology to record, in unprecedented levels of detail, patterns of movement, activity, and space-use of full herds of dairy cows under varying thermal conditions and indoor microclimates. Data will be collected for 12 months on the main study farm (CEDAR, Reading) and for shorter periods in summer and winter at 6 case-study farms with different building design and usage. Continuous sensor monitoring of barn microclimates (temperature, humidity, air quality) and detailed ventilation surveys will be combined with physiological measures (body temperature, production, health) to enable detailed analysis of how indoor-housed dairy cows respond to, and cope with, heat stress over different timescales.

We will use building engineering modelling approaches to determine indoor microclimates in different farm building environments and management systems, and how these microclimates affect, and are affected by, cow behaviour. We will work directly with farmer study groups in a participatory approach to evaluate a range of potential mitigation strategies to reduce heat stress impacts under current and future climate scenarios. Working with our industry Steering Group, we will provide practical evidence-based solutions to the UK dairy industry for preventing and managing heat stress.

We will use a combined ultra-wide-band positioning sensor and triaxial accelerometer to collect high-resolution data (0.1 Hz at 0.2m accuracy) of location and activity of full dairy herds continuously over extended timescales. Novel eartag sensors will collect body temperature of all cows, while a selected subset will be fitted with a rumen bolus to measure internal temperature and drinking behaviour. CCTV cameras will also monitor behaviour at specific locations. A network of temperature, humidity, CO2 and HN3 sensors will record microclimate data continuously. Airflow measurements will also be made at specific timepoints. A 12-month longitudinal trial (100 cows) will be undertaken at the University of Reading CEDAR research farm. Further case studies measuring microclimate data will be undertaken in two 4-week periods (summer and winter) at 6 commercial dairy farms with qualitatively different types of housing and farm management systems. Follow-up studies (4 weeks in summer) at two of these farms will explore the links between microclimate and behaviour in more detail.
Data analysis methods adapted from movement and spatial ecology (home range and space-use analysis, random walk change-point analysis) will be used to determine associations between behavioural (and physiological) responses, including social and herd level interactions, and microclimate over different timescales. An explanatory model directly linking behaviour and microclimate will be developed using the novel integrated Step Selection Analysis (iSSA) framework.Energy modelling techniques adapted from the field of building engineering will be used to determine thermal loading across different farm systems, including how cow behaviour is affected by, and may affect, microclimate variation. Using qualitative inputs from farmer Focus Groups, a range of potential mitigation strategies will be tested to explore practical solutions for heat abatement under a range of current and future climate scenarios