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It’s not too early to start thinking about summer heat stress

Contributed by Karl VanDevender Published on 08 July 2020

The heat and humidity of a typical Arkansas summer combine to make a stressful environment for lactating dairy cows. During hot summer weather, milk production may decrease by as much as 50% and reproductive proficiency of lactating dairy cows is greatly diminished. Some data indicate that only 10% to 20% of inseminations in heat-stressed cows result in pregnancies.

060520 vandevender heat stress

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Some signs of heat stress in lactating cows are obvious, especially reduced milk production and lethargic behavior. Moderate signs of heat stress may occur when the temperature is between 80°F and 90°F, with the humidity ranging from 50% to 90%. These signs include rapid shallow breathing, profuse sweating and an approximately 10% decrease in milk production and feed intake. As heat stress increases, the cow will show severe depression in milk yield and feed intake as her body temperature elevates. She will begin exhibiting more significant signs of heat stress, such as open-mouth breathing with panting and her tongue hanging out.

The first step to reduce heat stress is to provide cool water and shade for all milking and dry cows, plus heifers. Water is the primary component needed to make milk, accounting for over 85% of the content of milk. Also, water requirements increase as environmental temperature rises. It also is important that cows have water in a location that is close to shade, so they will not travel great distances for water in a hot environment.

Water should be placed away from the milking parlor but in an exit lane from the barn, as well as near the feeding location. Water should be available for cows near their loafing area, either in the shade of native trees or in artificial shade. Water also should be clean, fresh and approximately at ground temperature.

Shading cattle from direct sunlight is also very important, as this allows them to rest in a more comfortable environment. The possible sources of shade range from trees, to portable shade cloth structures, to permanent roofed structures. Each approach has its own set of advantages and disadvantages.

The second step to alleviate heat stress in lactating cows is to provide a more comfortable environment in the holding and feeding areas. Ideally, the holding pen area is cooled with a combination of shade, air movement and evaporative cooling water additions. When combined with air movement, added water can increase the cooling ability of the cow. However, adding water in humid or poorly ventilated holding pens can increase heat stress. If it does not evaporate from the cow, water can actually limit cooling.

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One system that works very effectively is to sprinkle water onto cows just long enough to wet their backs. Fans are then used to help remove evaporated water vapor away from the cows. When the cows’ backs are dry in a few minutes, the process is repeated.

Avoid allowing water to run onto the udder. If water does reach the udder, it is possible that bacteria can be transferred into the mammary glands resulting in more mastitis. If possible, blow air onto the cows continuously. However, in some cases fans may need to be off for the period when the sprinklers are running, so the water droplets land on the cows’ backs. The floor of the holding area should be grooved or rough-surfaced concrete or some other suitable footing so cows do not slip in the wet environment. As a general rule, water should not stand in the holding pen, and the feet of cattle should be exposed to limited water.

Also, care and design should be used to avoid unintended consequences with manure and heavy-use area management.

While temperatures are cool, advanced planning and implementation is a good way to get ahead of cattle heat stress and negative cow performance impacts. For additional information read Heat Stress in Dairy Cattle and Cooling Dairy Cattle in the Holding Pen.  end mark

Karl VanDevender, Ph.D., P.E., is a professor and extension engineer for the Department of Biological and Agricultural Engineering at the University of Arkansas. Email Karl VanDevender.

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