Negating weather-related stress on calves

Carole Curtis
Heat stress on dairy calves is an important health and welfare issue.

JUNEAU - If the cows are hot, their calves are even hotter.

The comfort zone for calves is even smaller than that of dairy cows, Dr. Geoff Smith told listeners during "Minimizing the Effects of Weather", a World Class Webinar presented by Professional Dairy Producers of Wisconsin.

"Dairy producers are very aware of the negative effects heat stress has on their cows because we all see our milk checks go down. We need to understand there is a negative impact on our calves, as well," he said. "Certainly, for health and welfare, we need to think about heat stress on our calves and what we can do to negate that."

For calves, heat stress kicks in at 78 degrees. "It's tighter than for cows," said Smith, North Carolina State University College of Veterinary Medicine calf expert.

The direct effect of heat stress on calves include reduced growth rates, decreased starter intakes, poor immune function, reduced response to vaccinations, and increased mortality.

Reduced growth rates

Several studies show a 20 percent reduced rate of growth with heat stressed calves, primarily due to decreased feed intake.

One study on heat stress documented dry matter intake (DMI) decreased by 20 percent, while another showed an 8 percent decrease in DMI, a 30 percent increase in water consumption and a 26 percent decrease in weight gain. "The calves were eating less and drinking more," Smith observed.


A growing body of literature suggests heat stress has negative impacts on a calf's immune function. Some farms report more health challenges in the summer months, Smith observed, and abomasal bloat rates often increase.

 Abomasal bloat, also called "sloshy gut" or "watery gut" tends to hit calves between 5 and 10 days of age. Diarrhea is not involved, but something, perhaps clostridia bacteria, is interfering with abomasal emptying. Mortality rates can be very high.

"It seems sporadic, but some farms have multiple outbreaks," Smith noted.

Heat stress may play a role in slowing abomasal emptying, given calves in the Southeastern states seem to be more susceptible. "We must be careful with feeding high volumes and feeding high-fat," Smith said.

The keys to preventing bloat are to make sure the milk replacer mixture and the feeding schedule stays consistent, and that the meal is not too hot.

Make sure appetizing water is always available to each calf and avoid large volumes per feeding. Some Southern dairies go to three feedings a day during the summer to keep calves up to snuff.

Smith also suggested taking samples of the milk replacer given to the first calf, a middle calf and the last calf to ensure consistency. "You don't want the total solids and Brix to jump around," he said.

Preventing heat stress

There is plenty dairy farmers can do to keep heat stress at bay, including improving airflow and ventilation with fans in calf barns or openings in calf hutches.

Shade calves in hutches. "A lot of us think hutches will provide shade, but they are more like little ovens," Smith said, noting plastic hutches run internal temperatures 8 - 12 degrees higher than wood hutches or pens.

Some farmers situate umbrellas over their calf pens, while others use hutch covers to provide shade, which can decrease the temperature inside a hutch by 13 degrees. Shade cloth can be suspended over an entire set of hutches or hutches can be shaded individually.

Calves bedded with straw stay cooler than calves bedded on sand, Smith noted.

Another option is radiant heat covers (, which can lower temperatures inside a hutch by 10 degrees by reflecting the sunlight. In Texas, a cover will last the summer. "They're not really durable, but if you can't get your calves under shade, this is a relatively inexpensive fix," Smith noted.

When calves sweat, they lose water and electrolytes, mainly potassium. The treatment for heat stress, therefore, is different than for diarrhea, which focuses on replacing energy and correcting dehydration.

Based on the composition and cost, Entrolyte HE (R) is not recommended for HS. Instead, Smith suggests Land O' Lakes'Electrolyte "Base + Add" System, and using just the electrolyte base at the rate of two scoops per five gallons of water, which tallies about $0.25 per calf per day.

"It's similar to Gatorade," he observed, urging dairyman to commit to feeding electrolytes throughout the summer as part of their efforts to reduce heat stress and maintain the health and welfare of their calves.