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Heat stress can be a problem all year, or just for a part of the year. Providing proper ventilation has a dramatic effect on overall productivity and comfort. Dairy cows not affected by heat stress produce more milk; have lower respiration rates, higher conception rates (resulting in more cow pregnancies) and overall better health. When cows are comfortable they lie down and thereby produce more milk, so this is the wanted behavior and it can be induced by using the correct ventilation design and equipment.
The actual feel of a temperature level for the cow increases with Relative humidity levels. If the temperature is 18oC and the RH level is below 20%, the cow will feel the temperature as it is. But as the RH levels increase, the temperature is perceived as being much higher. At an RH level of 80% the cow will feel the temperature is 21oC. This escalates with higher temperature levels. If the temperature is 28oC it is enough with a RH of 30% for the cow to feel a temperature increase of 3oC. At a 90% relative humidity and temperature of 33oC, the heat stress levels are becoming severe.
Temperature and relative humidity help the farmer to determine the risk of heat stress, but other factors that influence the cow's wellbeing include wind speed, the cow’s weight and production level. These parameters should be included when looking at the problem of heat stress because a high producing cow is more sensitive to high temperatures than a cow with normal production. The wind chill effect and if the animal’s skin is wet, will also make the cow feel cooler.
How can heat stress be detected?
Cows are able to let the farmer know that they feel the temperature is too high. The signs are:
When the cows show signs that they are out of the comfort zone and feel heat stress, the farmer has a lot to gain from improving the climate system in the dairy barn and milking parlor to avoid the previously mentioned negative impact on the production results, reproduction rates and the increased risk for infections. New results published in 2013 also show that heat stress during the late gestation period, has a negative influence also on the calves and milk production.
Climate and weather studies alert on that more extreme weather types can be expected for the future, including more humid and warm summers, without sparing any part of the world, completely altering the climatic map as we know it.
How can heat stress be counteracted?
Keeping the climate as stable as possible inside the barn to mitigate drops in productivity is a necessity for intensive farming of today. The cow’s ability to produce milk is dependent on that she eats and that the feed intake is consistent. If it is not, production rates will decrease.
The first criterion Munters experts look at is the ambient climate condition of the specific location. Average summer temperatures and humidity levels as well as other specific weather scenarios are things that the climate control system needs to be ready for, and these facts and statistics are carefully collected and investigated. The barn system and how the cows are stalled are other parameters that affect the design and layout of the ventilation system.
Installation of cooling equipment of some kind is quite common today. Even shorter periods of warm weather and elevated RH levels negatively affect the milk production, fertility, conception and pregnancy rates of the cow. At moderately high temperature and humidity levels, it can be enough to create a wind chill effect over the animal’s body by using fans to generate a high enough air speed (3 m/s) over the animal’s skin, in order to ensure sufficient heat removal. At higher temperatures and humidity levels it is an absolute necessity to use cooling equipment in order to keep up with required production levels.
Naturally ventilated barns
For naturally ventilated barns, our experts would recommend a misting system which sprays a fine mist over the cows during the hottest period. Correctly placed nozzles can create a temperature reduction of 5°C.
The use of a misting system has another advantage; it can also be used to soak the stable or barn to prepare it for cleaning.
Naturally ventilated buildings are often constructed with an open ridge. Ridge ventilation provides an excellent combination of ventilation and light dispersion. The designs of the ridge vent and wind deflector result in a vacuum effect, which effectively sucks out the warm and stale air inside the barn/stable.
Ventilation panels provide an excellent combination of ventilation control and light requirements and form an integral part of the natural ventilation for livestock stables. The panels are made of insulated and UV resistant polycarbonate sheets, characterized by ease of operation and optimal airflow for minimum cold ventilation.
Curtains are often used in dairy buildings and there is a wide array of curtains for intensive dairy farm operations, of which the most prominent ones are in TEX glass quality. This material is UV resistant, allows daylight penetration and is treated against static electricity, which means that dust and dirt does not stick to the material. Curtains form a natural wall inlet that allows for both cross ventilation and ventilation driven by the vertical chimney effect. At the same time it serves as climate shield against draft, rain, snow and hail to ensure that the animal is in the comfort climate zone.
The primary use of large circulation fans in livestock housing is to provide comfort cooling to the animals. For this very purpose, it is wise to use specifically designed circulation fans to provide the maximum cooling footprint at animal level. Dairy barn circulation can be optimized by offering several mounting options and the possibility to tilt the fan in order to provide the best airspeed footprint. The airspeed footprint is defined as the area in which the average airspeed exceeds 2m/s. Fans with large cooling footprint give less “dead spots” in the barn and equate to improved milk production for the farmer.
Another piece of the natural ventilation puzzle is a high volume low speed ceiling fan, engineered to circulate a vast amount of air, providing an efficient air circulation movement for animal housing. Such a ceiling fan creates slow, gentle breezes to lower the effective temperature during warm periods and to circulate the rising warm air downward to ground level during cold periods. In addition, the fan will reduce humidity, moisture, condensation and odors, creating a healthier and more comfortable environment.
Enclosed dairy barns with forced ventilation
If we now move to looking at enclosed buildings with forced ventilation which is mainly used in moderate and hot climate areas, cooling is predominantly achieved by use of evaporative cooling pads, framed by a gutter system and serviced by a water tank and pump. The evaporative process takes place by use of extraction fans usually placed on the wall across from the cooling pads (cross ventilation) or at the gable end of the stable extracting cool air from the pads all along the house (tunnel ventilation). This pad cooling set up can provide up to 10°C temperature reduction depending on the ambient conditions.
The climate components installed in the house are automatically managed by a control unit and by means of a communication system. The farmer can check the climate system in the dairy house directly from his own PC. Modern controller units receive all inputs, process the data and all output signals are sent by the Farm Hand Dairy with the ability to control and manage 3 temperature zones and controls ventilation through THI index values or temperature. The device can handle the misting system and soaking cycles as well as curtains to set temperature. A wind meter sends signals to the controller when winds are too strong, which in its turn will close the curtains tight.
Dips in milk production can be avoided. A carefully designed an optimized ventilation or climate control system can help farmers, anywhere in the world, to maintain a sustainable production level and comply with commercial agreements, often at an average payback time of less than three years.