Summer heat

A herd of dairy cows along Laurel Road in Brecknock Township, Lancaster County, Pa., congregate in the shade of a tree to escape the summer heat.

Summer is just around the corner, and it’s sure to bring sun, fun — and heat stress in dairy cows.

Holsteins are most comfortable when the temperature is between 30 and 70 degrees.

They get their wish most of the time, but when the mercury climbs, cows eat less and make less milk, said John Tyson, a Penn State Extension agricultural engineer.

Tyson spoke in an April 16 webinar.

Returning a cow to maximum production after heat stress is important, but the recovery period is dependent on the time spent in high heat and humidity.

Without proper attention, she might never reach peak production, said Izabella Michelon Toledo, a University of Florida Extension dairy agent.

Heat stress can lead to myriad health problems, including acidosis, low calf birth weights, reduced reproductive performance and lameness.

Hot cattle will stand for extended periods to release heat, but all that standing can create claw horn lesions on the hooves.

Calves can have reduced absorption of important colostrum antibodies called immunoglobulin, Toledo said.

Given the mountain of problems associated with heat stress, prevention is the best, and easiest, medicine.

“Simple thing — decrease the solar load,” Tyson said.

In engineer-speak, that means to get the cows some shade.

Night grazing, barn shade curtains, or even a tarp hung over an exposed rest area can all do the trick.

Other strategies reduce the temperature around the cow.

In freestall barns, fans and misters are often placed over the feeding or rest areas to encourage cows to spend more time there.

“Better bang for our buck if we focus on the resting area,” Tyson said.

Fans exchange the stale barn air with fresh air from outside, but the air needs to move at least 3.5 mph to get through the cow’s hair to its skin.

Misters and foggers relieve heat through evaporation.

However, if the fans or wind are not strong enough to blow the wetness off the cows, the water can form a thin layer and trap heat, putting the cow in greater danger than before, Tyson said.

Water doesn’t have to be sprayed to be helpful, though.

When hot weather is coming, farmers should make sure their cows have plenty to drink.