Keeping cows cool with sprinklers
Published on Thu, 05/17/2018 - 9:49am
Keeping cows cool with sprinklers
By Michael Cox for American Dairymen Magazine
Summertime is upon us and with high temperatures set to continue for the coming months, cow cooling will play an important role on farm performance and profitability. The economic cost of heat stress due to lower milk production and reduced liveweight performance is well known, and is estimated to amount to $6 billion across the country annually. One of the most effective methods of cooling cows during summer is the use of water sprinklers or misters in holding pens and feed lanes.
Before starting any form of cow cooling practices, dairy staff should be aware of the temperature-humidity index (THI) and how it effects heat stress in dairy cows. This color-coded index illustrates various levels of heat stress in cows, depending on two variables; air temperature and relative humidity. Research from Michigan State University suggests that mild heat stress can begin at just 65 degrees F. Just like in a sauna, high humidity creates heat stress at a greater rate than high temperatures combined with ‘dry’ low humidity conditions. Milk yield losses of 5lbs per day can begin at THI levels between 65 and 74. As modern dairy cows are large, high performing animals with massive metabolism rates; cows will feel hot and under heat stress long before people begin to feel uncomfortable. Therefore, it is important that farm staff pay close attention to THI and begin cooling cows before the onset of heat stress. Many modern water sprinkler cooling systems are fitted with sensors to control the turning on and off of sprinklers; effectively eliminating the risk of human error.
Low-pressure versus High-pressure
Cooling cows with water can take two forms; low-pressure sprinklers or high-pressure misters. Both methods reduce heat stress through evaporation. In the low-pressure method, water is sprinkled onto the cow’s body, before evaporation removes heat energy from the cow’s skin. Generally, the sprinklers should run for 2 to 3 minutes and fully ‘soak’ the cow’s skin. The sprinklers should then be turned off for approximately 15 minutes, to allow time for evaporative cooling. Constant sprinkling will not cool cows, as little evaporation will take place and humidity will increase. Grazing dairies using center-pivots to cool cows during summer will notice how cows will self-regulate cooling; spending short periods of time under the pivot sprinklers before moving out to the pasture to evaporate and cool down. The situation is similar for confinement-based cows.
Recent research from University of California, Davis, indicates that increasing the water flow rate in low-pressure systems does not have any additional benefits. The study found no difference in heat-stress or animal performance between cows sprinkled with 1.3 litres per minute, compared to 4.9 litres per minute. This is the first study of its kind to look at water flow rates, and the initial results should encourage further research to help dairymen reduce water consumption and increase sustainability.
Under the high-pressure misting system, the mist evaporates from the air, and therefore lowers the air temperature surrounding the cows. Research from Minnesota State University suggests that a water pressure of 200 lbs per square inch is required to create a fine mist that is easily evaporated. This is approximately 10 times the water pressure required versus the low-pressure sprinkler systems. Different nozzles and filters will be required depending on which type of system is operated. High-pressure systems can be run constantly if necessary, as the air (and not the cow) is responsible for the evaporating effect.
As humidity is such a crucial factor to heat-stress, water sprinkler systems can easily increase relative humidity, unless adequate ventilation and air flow is in place to draw in drier air and force out hot, higher humidity air. Fans can be placed close to nozzles to ‘push out’ hot air. In cross-ventilated barns, fans along the inlet side of the barn will control the direction of the mist and rate of air-flow. Generally, high-pressure sprinkler systems are more suited to drier, arid parts of the country, with low-pressure systems preferable in more humid regions.
Regardless of which type of sprinkler system is installed, dairymen should aim to use micro-sprinkler nozzles instead of larger nozzles. Micro-sprinklers are small greenhouse type nozzles which can spray water in 90 degrees, 180 degrees or 360 degrees radius. The smaller nozzles will allow for a more even spread of water across the pen compared to larger nozzles. 180 degree nozzles work well along feed lanes and typically spray water 6 to 8 feet from the water line. Nozzles should be spaced apart at a maximum distance of the diameter of spray, however it is advisable to place nozzles closer together to ensure full spray coverage, particularly if fans are used in the cooling system.