You may be tired of hearing about heat stress, but your cows are not

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A few unseasonably warm days in late April not only melted most of the snow but also reminded us to turn our attention to heat abatement. The effects of heat stress are well documented and costly to the dairy farm as they impact a variety of performance parameters, including milk yield, growth and reproduction.  
Temperature humidity index is a metric that combines temperature and relative humidity, and it is commonly used to evaluate risk of heat stress. High-producing dairy cows can become heat stressed at a THI of only 68. If you haven’t already done so, start thinking about heat abatement strategies for your dairy cows.
The first line of defense against heat stress is to provide shade to animals. Next, the combination of air velocity, water and time are all key factors to effective evaporative cooling of cows.
Work with your management team to prioritize mechanical heat abatement strategies on your farm. Several resources are available to assist in this process. It is imperative that cows feel comfortable enough that they want to go to the feedbunk to eat. Also focus on the areas where heat stress is most severe, such as parlor holding pens. A well-managed cooling system with fans and/or sprinklers will help in these areas.  
Providing access to clean, fresh water is critical during summer months. Lactating dairy cows re-quire between 25 and 35 gallons per day. Water intake may double during periods of heat stress. Provide 3 to 4 inches of linear water space per cow along with a minimum of two water locations per group. Check water flow rates during times of high demand and clean waterers regularly. Availability of clean water to cows leaving the parlor is beneficial for increasing water intake during heat stress. This can be accomplished with temporary, low-cost waterers.
Certain dietary strategies can be beneficial during heat stress, but the biggest impact will come from focusing on forage quality along with forage and feedbunk management. Minimize the amount of time feed is defaced from bunkers or piles. Provide a majority of the ration during cooler periods of the day to promote greater dry matter intake. Intensity of feed push-up and frequency of feeding can encourage more frequent meals and reduce slug-feeding that naturally occurs during heat stress. If feed stability is an issue, consider adding dry propionic acid to the total mixed ration on hot, humid days.
From a nutrition standpoint, no silver bullet perfectly combats heat stress. Benefits can be seen by increasing certain minerals; potassium, sodium and magnesium contribute to an increase in dietary cation-anion difference levels in lactating dairy cows. Potassium is a primary regulator of water secretion from cows’ sweat glands and is secreted at high levels in milk. Research has shown feeding elevated DCAD levels during heat stress has resulted in improved milk yield and milk fat test. Research-proven additives to consider during periods of heat stress include additional buffers, salt, yeast, bypass fat, niacin, Rumensin® and Aspergillus oryzae.
Researchers at the University of Florida recently concluded that minimizing heat stress in dry cows is a valuable management tool to improve performance in the next lactation. Results from three consecutive years concluded that cows heat stressed during the dry period will produce, on average, 13 pounds less milk than cows that are cooled during the dry period. In addition, these studies showed lower immune status and lower calf birthweights from cows exposed to heat stress during the dry period. More re-cent research confirms this reduction in performance in the daughters and granddaughters of heat-stressed cows, making this a multigenerational challenge.
Reducing heat stress requires careful consideration of management and nutritional practices. Pro-vide a well-managed cooling system in your dairy barns first and then look at what feeding strategies and nutritional additives may give you the most economic benefits.  
    Barry Visser is a nutritionist for Vita Plus.

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