Heat stress has been shown to affect aspects of innate immunity, such as the production of oxygen radicals by neutrophils in response to stimulation. “This means that heat stress may impair the ability of cattle to fight off infection in the first hours or days after infection, when the innate immune response is protecting the host while the acquired (memory) immune component of the response is gearing up,” Woolums explains.
Heat stress at the wrong time could conceivably affect the longterm immune function in cattle that were infected or vaccinated during significant heat stress.
Neonatal calves need extra help
There is also some evidence that colostral antibody absorption is decreased in calves born to cows that are heat-stressed late in gestation.
It’s imperative, especially with neonatal calves, says Leadley, to help them out during these times. “These little calves are not going to do anything themselves to make the situation better such as stand up or move to a different location.”
And it’s not just the little calves that can be affected, points out Lance Baumgard, associate professor of animal science at Iowa State University.
Older calves can suffer from heat stress as well, but sometimes they are “forgotten about” as they grow. Heat stress can be a factor for them as well, even if they are on pasture. “Solar radiation (sunlight) is very intense,” Baumgard says. “Shade, airflow and plenty of drinking water is of primary importance for calves on pasture.”
So, it’s imperative to put these animals in situations where they can avoid the deleterious effects of heat stress.
COMMUNICATE ABOUT HEAT STRESS
Sam Leadley has had first-hand experience with a heat-stressed newborn calf that caused him to think differently about handling calves in those situations — and the need for better communication on the dairy.
“To be effective in dealing with heat stress with newborns, all of the care-givers need to have heightened awareness of the danger,” explains Leadley, a calf-care expert affiliated with Attica Veterinary Associates in Attica, N.Y.
He notes a time when a calf was dropped off at his barn on a very hot day. The person dropping the calf off had picked up the calf in the trailer, and then dropped it off in the first open hutch he found.
Later, Leadley says, “I kicked myself around the block when I found her close to death. The person dropping her off wasn’t thinking about extreme heat stress when she wouldn’t stand up and never said anything to me about her being weak.” It was oppressively hot (close to 90 degrees F, 80-percent-plus relative humidity) and Leadley says he should have gone out to check on her right after she arrived.