Heat Stress Mitigation Strategies

Summer’s heat is great for trips to the lake and laying out poolside, but the heat can take a toll on the well-being of dairy cows. When cows experience heat stress, they eat less, produce less milk, have reduced immune function leading to increased disease, and have more difficulty getting bred. All these issues significantly affect the farm’s bottom line. With each summer seeming to get hotter, it is essential to have strategies to reduce heat stress and improve the animal welfare of the dairy cow. Three strategies to keep in mind for mitigating heat stress are shade, ventilation, and water-based cooling.

Cows should be evaluated at different times of the day to assess their level of heat stress. During the hotter temperatures of the afternoon and early evening, signs of heat stress may be more noticeable. Those signs include panting, increased respiration, sweating, and less lying time. If you see these signs, it may be time to reevaluate your cooling protocol.

It is critically important that all cows have shelter from the hot summer sun. Most dairies operate under full confinement, with cows housed in barns throughout the year. Barns should be designed and built to maximize the amount of shade cows receive throughout the day. Barns that maximize shade should have a north-south orientation on the long side. Curtains often used to block the cold winds in winter can also be appropriately utilized to increase shade during certain times of the day. If a farm uses curtains, it is crucial to maintain adequate ventilation, which is critical for cooling and overall animal health. Dairies that allow cows access to a pasture or dry lot should provide appropriate shade in permanent run-in sheds or movable shade structures.

Good ventilation in the dairy barn consists of air exchange and fast air movement. Air exchange involves moving out warm and humid air and any noxious gases such as ammonia and bringing in fresh, cooler air. This improves the well-being of both the cows and employees of the dairy. In  the summer, 40-60 air exchanges should happen per hour. Fast air movement is also significant for cooling as it helps cows dissipate heat. Fast air movement should be present in all barn areas, including the parlor, holding pens, feed bunk, and free stall or bedded pack. The ideal fast airspeed is 400 feet per minute at the height of 20-30 feet over the stalls or pack. Both can be accomplished with natural or mechanical ventilation. Natural ventilation takes advantage of prevailing winds and can be very cost-effective. Near the edges of the barn, incoming wind may provide high airspeeds that lessen the need for fans. Towards the middle of the barn, fans spaced close together and at the proper angle ensure that cows lying in stalls are appropriately cooled. Mechanical ventilation forces air movement through the barn using exhaust fans. These can be set up as a tunnel system with fans on the short side of the barn and air moving parallel to the feed bunk or as a cross-ventilation system with fans on the long side and air moving perpendicular to the feed bunk. Baffles may also be necessary in these barns to push fast-moving air down onto the lying area. Some mechanically ventilated barns may still need additional overhead fans to force high-velocity air over the cows.

Water-based cooling
Water-based cooling can be accomplished with either misters or soakers. Misters push a fine mist of water into the air, lowering the overall air temperature yet increasing the humidity. This works well in low humidity areas such as the southwestern US. On the other hand, soakers spray large droplets of water over cows to wet their skin. A cow’s body heat then evaporates the water, causing a cooling effect. This cooling effect is increased with fast air movement from fans. Soaker nozzles should deliver 1 gallon of water over the spray period of 3 minutes or less, and systems should be set to spray at least every 15 minutes. Soaking is a very effective cooling method and reduces respiration and body temperature and increases feeding time and milk yield. In addition to water sprayed over the cows, it is critical to provide cows with plenty of fresh drinking water. Drinking fountains should be available in the pens and going to and from the milking parlor. If you see cows are crowding their waterer in the pen, you may consider adding additional tanks during warmer months.

Holding pens are an area often overlooked when improving cooling systems. Holding pens frequently have poor ventilation and are often very crowded for a significant amount of time. These issues can be overcome with high-velocity fans combined with soaker sprinklers and taking care to give cows more space on hotter days by not packing the holding area.

The cooler months are a great time to ensure all your fans are in working order. This is also an excellent time to repair or replace curtains and baffles. Soaker systems should not be tested when it is very cold. In spring, soakers can be evaluated to ensure all nozzles are working and there are no leaks in the line. Mitigating heat stress requires a multipronged approach, but providing shade, ventilation, and water-based cooling can hugely impact productivity throughout the summer. ◄