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    With seasonal temperatures finally upon us, it is a great time to make sure heat abatement strategies in your farm are up to par. 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, lameness, compromised immune systems and reproduction. Temperature humidity index is a metric that combines temperature and relative humidity and is commonly used to evaluate risk of heat stress. High-producing cows can become heat stressed at a THI of only 68.

Drinking water is essential
    Providing access to clean, fresh water is critical during summer months. Lactating dairy cows require between 25 and 35 gallons per day. Water intakes 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. It has been documented that cows will drink up to 35% of their daily water needs when returning from the parlor if available. This can be accomplished with temporary, low-cost water options. Return lane waterers should provide 2 feet of linear space for each cow exiting the parlor at one time. For example, a double-16 parlor with one side exiting at a time should have 32 feet of linear water space.

Fans, sprinklers
    It is imperative you first provide a well-managed heat abatement program with fans and sprinklers that allows the cows to feel comfortable enough that they want to go to the bunk to eat. Four key components of cow cooling are shade, air velocity, water and time. If you haven’t already done so, make sure fans and sprinklers are clean and in good working order. Dust on fan louvers or the shields of basket fans can reduce air output up to 40%.
    The holding pen is a top priority for heat abatement on most farms. Use soaking systems that provide short, frequent soaking with large droplets. These larger droplets penetrate the hair coat to reach the skin for more effective heat transfer. Combined with air velocity of at least 4 to 6 mph, evaporative cooling will effectively be achieved.
    Don’t forget the dry cows. Researchers at the University of Florida 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 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.

Feedbunk, nutritional strategies
    Certain dietary strategies can be beneficial during heat stress, but the biggest impact will come from focusing on forage quality along with forage and feed bunk management. Minimize the amount of time feed is defaced from bunkers or piles. Deliver most of the ration during cooler periods of the day to promote 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 TMR on the hot, humid days.  
    From a nutrition standpoint, no silver bullet perfectly combats heat stress. Benefits can be seen by increasing certain minerals, such as potassium, sodium and magnesium; all contribute to an increase in dietary cation-anion difference levels in lactating dairy cows. Research-proven additives to consider during periods of heat stress include additional buffers or salt, yeast, bypass fat, niacin, chromium, Rumensin® and Aspergillus oryzae.
    Reducing heat stress requires careful consideration of management and nutritional practices. Provide a well-managed cooling system in dairy barns first and work with a nutrition advisor to look at what feeding strategies and nutritional additives may provide the most economic benefits.
    Barry Visser is a nutritionist for Vita Plus.

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