Heat stress occurs when the animal's thermolysis mechanisms are not sufficient for it to be able to regulate its body temperature. Cows in conditions that are not within their thermoneutral zone (from 5º to 25ºC) have higher metabolic requirements, respiratory rate and will struggle to regulate body temperature.
Minimize and control heat stress in dairy operations is essential to ensure herd health, normal behavior and milk yields.
Recent studies review and refer methods for managing heat stress. This article will brielfly provide information on the latest research, focusing on environmental modifications, dietary adjustments, physiological approaches and innovative Precision Livestock farming (PLF) options to control and mitigate heat stress in dairy cows. We invite the reader to access the reference list for further information on this topic
Controling heat stress
The most common control and mitigation technique used to fight heat stress for dairy cows is to control the animals' thermal environment, however, climate control systems can be costly, and therefore limited in use. Cooling strategies for cows follow four general thermodynamic principles of heat transfer: conduction, convection, radiation and evaporative cooling. Two of the most effective environmental strategies involve cooling systems and shade provision.
Cooling Systems
Ventilation and air circulation
Adequate ventilation is an essential parameter for dairy housing. Good ventilation ensure air quality inside the instalation and promotes heat exchange. Tunnel-ventilated instalations seem to perform slightly better than naturally ventilated instalations by keeping the inlet and outlet temperature differential lower and thus promoting higher ventilation. This of course depends on several factors and the climate of the area. Regardless of the configuration of the barn ventilation system, adequate airspeed near the cows is important to control heat stress and promote heat transfer.
Evaporative cooling solutions
Evaporative cooling uses water to promote heat transfer from the animals. We can have direct cooling systems (that apply water directly to the animal and thus promote heat loss) or indirect systems (lower the temperature of the air increasing heat transfer).
- Examples of direct systems: Sprinkler/shower systems that wet the cow with large water droplets to provide cooling. Sprinkler systems are better suited for high humidity.
- Examples of indirect systems: Misting and fogging systems rely on small water droplets evaporating using heat in the air to evaporate water, lowering the dry bulb air temperature. Fogging systems, also called high-pressure misting systems, produce smaller water droplets than typical misting systems.
Once evaporative cooling systems incorporate adding water to the animal space air, ventilation systems that provide a good air exchange to remove moisture-laden air, and circulation fans to enhance evaporation are beneficial to add to them.
Roof and Shade Structures
The type of roof/shading materials can minimise the solar load (radiation heat transfer), reducing the overall heat load on the animal; in this way, evaporative, convective, or conductive cooling will be more able to provide adequate cooling. Farm buildings orientation should be in order to provide maximum shade under the roof. Reflective roof materials (aluminium or white coloured galvanized material) have been shown to significantly reduce heat absorption.
Precision Livestock Farming Techniques
PLF technologies can enable automatic, continuous, and real-time cattle heat stress monitoring and mitigation under field conditions.
On-Animal Sensors such as respiration rate monitors, location trackers with integrated temperature and motion senssors, accelerometer based sensors, ear tags with subcutaneous temperature sensors have been shown to provide real time individual information that can be used to act when heat stress starts to occur in individual animals.
Off- animal devices and tools can aid in preventing or anticipating heat stress probability to occur. Weather data applications, video image durveillance and Infrared Thermography (IRT) can be grouped and used.
PLF technologies are growing each day. To provide farmers and practicioners with amaxzing tools to aid management.
Integrated management practices
Information, observation and integrated management are a must have to ensure heat stress control. You can have the best cooling systems and buildings, but if farm personel is not welll informed and engaged in preventing and detecting heat stress situations, or management practices are not being integrated, you will be losing efficiency.
Simple management practices can make a difference:
- Bedding: heat stress can be increased in low quality, dirty and/or compacted bedding. Regular cleaning and bed replacement, joint with good ventilation will provide better quality for cows.
- Nutrition: The adjustment of diet (to reduce the negative effects heat increment) can be used as a potential mitigation option, also ensure adequate energy intake (feed intake is usualy reduced in heat situations, and higher energy demands for ensuring thermoregulation. Having a cartified nutritionist will ensure that diets are formulated ensuring production yield and adapting to eat stress situations.
Lets not forget: WATER
Having ad libitum, clean and fresh drinkable water is the number one factor to ensure hydrated animals in the farm. In a heat stress situation, cows will increase water consumption.
Take home messages
Effective control and management of heat stress will improve welfare of dairy cows but also aid in ensuring milk yield, making dairy operations more efficient and economically viable in the face of climate challenges. The increasing impact of global warming and rising temperatures makes heat stress control in dairy cattle an increasing challenge.
References
Ji,B., Banhazi, T., Perano, K., Ghahramani, A., Bowtell, L., Wang, C. and Li, B. 2020. A review of measuring, assessing and mitigating heat stress in dairy cattle. Biosystems Engineering, Volume 199, Pages 4-26.
(https://www.sciencedirect.com/science/article/pii/S1537511020302026)
Dean, L., Tarpoff, A.J., Nickles, K., Place, S., Edwards-Callaway, L. 2023. Heat Stress Mitigation Strategies in Feedyards: Use, Perceptions, and Experiences of Industry Stakeholders. Animals, 13(19):3029. https://doi.org/10.3390/ani13193029
Islam Md. A., Lomax , S., Doughty, A. Mohammed. I.R., Ollie, J., Thomson, P. , Clark, C. 2021. Automated Monitoring of Cattle Heat Stress and Its Mitigation. Frontiers in Animal Science, VOLUME 2 (https://www.frontiersin.org/journals/animal-science/articles/10.3389/fanim.2021.737213)
Chung, H., Vu, H., Younghyun, K. and Choi, C.Y. 2023. Subcutaneous temperature monitoring through ear tag for heat stress detection in dairy cows. Biosystems Engineering, Volume 235,Pages 202-214.(https://www.sciencedirect.com/science/article/pii/S153751102300209X)
Grinter, L.N., Mazon, G. and Costa, J.H.C. 2023. Voluntary heat stress abatement system for dairy cows: Does it mitigate the effects of heat stress on physiology and behavior? Journal of Dairy Science, Volume 106, Issue 1,Pages 519-533. (https://www.sciencedirect.com/science/article/pii/S0022030222006774)
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