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Here in the midwest, we have just experienced one of the hottest Junes on record. And, more of the same is expected for the remainder of the summer. While we do a much better job of minimizing heat stress on cows than we used to, we still have room for improvement.

The milking herd is often the sole focus of heat-abatement efforts because failure to do so results in devastating production losses. However, three other groups of animals are significantly at risk for heat stress, too. Unfortunately, we often overlook them because the consequences are not immediate.

  • Baby calves.
    While we routinely recognize that cold temperatures increase the energy requirement of animals — especially calves — we sometimes forget that any temperature outside an animal’s thermoneutral zone, including very high temperatures, increases its energy requirement, too.

    Heat stress leads to reduced dry matter intake. Even if health is not compromised in these young calves, growth very often is. If calf hutches are not shaded, they can become extremely hot. Ample water must be provided. Under very hot conditions, an extra feeding of oral electrolytes will help provide calves with the  fluids, energy and minerals needed.

  • Dry cows. 
    On many farms, dry-cow facilities are haphazardly designed. Therefore, cooling these areas often presents a challenge.  

    Heat stress in dry cows leads to decreased dry matter intakes at a time when their energy requirement actually increases. Dry cows subjected to heat stress have calves with lower birth weights.  And heat stress on the close-up dry cow further aggravates her tendency toward reduced intake and excessive fat mobilization. This scenario often becomes the perfect recipe to trigger fatty liver and its consequences. In addition, immune function will be compromised to an even greater extent.

    Research has shown significant benefits to cooling dry cows, including an improved transition period with less disease and culling, along with improved milk production in early lactation. In addition, cooling cows during the dry period results in fewer cows being culled for reproductive reasons. Make sure your dry cows — especially the close-up dry cows — are cooled at least as well as your lactating cows.

  • Sick cows. 
    In many herds, sick cows are isolated from the lactating cows in a separate pen or area of the barn. Unfortunately, this spot is not usually as well-ventilated or cooled as the lactating-cow area. Cows with displaced abomasums, ketosis, mastitis or uterine infections all have disturbances in their blood-electrolyte levels. Under conditions of heat stress, significant amounts of sodium and potassium are often lost through sweating. This can further disrupt the electrolyte balance in a sick cow. 

    In my practice, we have treated several down cows in the last month with low blood-potassium levels — probably as a result of a metabolic condition coupled with heat stress. Using heat-abatement strategies for cows recovering from an illness will help speed their return to health — and may prevent a downward spiral of disease.

Invest in heat abatement

During these hot summer months, establish an effective system to cool your herd, including shade, ventilation and water. Make sure all of the animals have plenty of water and salt. And don’t neglect to cool the three groups of animals that are as vulnerable to heat stress as lactating cows — baby calves, dry cows and sick cows.


Brian Gerloff is a veterinarian and operates Seneca Bovine Service in Marengo, Ill.