The old saw, “it’s not the heat, it’s the humidity,” is not true for calves, according to Sam Leadley, PhD, calf and heifer rearing specialist with Attica Veterinary Associates, Attica, NY.

Leadley says both heat and humidity affect calf comfort and behavior, and that ambient temperatures of 80°F can produce high enough humidity to create heat stress in calves.

“With a temperature change from 70°F to 80°F, it has been estimated that water intake goes up 33 percent,” says Leadley. “And, when the temperature jumps from 70°F to 90°F, a 100-percent increase in water intake should be expected.”

Calves experiencing heat stress will show decreased feed intake; increased water intake; and increased standing time, respiration and panting. Their immune response to disease challenges is weakened; vaccines work less well or not at all; and rapid dehydration is common.

To manage heat stress in calves, Leadley says clean, fresh water available at all times is a must. Adding a direct feeding of water also can be helpful. Air movement also is critical. And, Leadley advises minimizing handling heat-stressed calves between 10:00 a.m. and 10:00 p.m.

To read more of Leadley’s advice on hot weather and calves in his Calving Ease newsletter, follow this link: