Editor's note: Geni Wren is former editor of Bovine Veterinarian, a sister publication of Dairy Herd Management. She now works for the American Association of Bovine Practitioners.
Young calves and heifers may be more heat-tolerant than older animals in production, but heat stress can still have negative effects. Calf-care expert Sam Leadley, of Attica (N.Y.) Veterinary Associates, says heat stress can have many negative effects on young calves.
When calves are heat-stressed, negative effects include suppressed appetite and intake.
Leadley says he always had his poorest rates of gain with calves born after the middle of June in western New York. “I never had any problems getting them to drink milk on a twice-a-day feeding system even when feeding 4 quarts each feeding of powder mixed at 15 percent solids (2.5 lbs. daily) between three and five weeks of age,” he says. “But hot weather just killed calf starter grain intakes. Even when I cut back the milk powder by half during the fifth week (dropped the afternoon feeding), they just did not come up on grain in the summer heat like they did between December and March.”
And, if dry matter intakes are down, so is their rate of growth.
While Leadley says he has seen fewer pneumonia cases during hot weather, diarrhea cases could turn more deadly than at other times of the year. “With scours, I really had to jump on dehydration issues because once a calf started with a severe diarrhea case, she could be down and gone in 24 hours in blistering hot weather. So, I usually spend more time on ‘poop-patrol’ in very hot weather. If I missed a calf that needed fluids, she could be down and gone fast.”
While there isn’t much research specifically looking at the impact of heat stress on immunity in the calf from birth to weaning, there is research indicating that heat stress can impact immune function in older cattle, so it’s logical to assume there is also an effect in the pre-weaned calf, says Amelia Woolums, veterinary researcher at the University of Georgia.
Woolums says there is some research indicating that heat stress can affect the response of immune cells in young calves.
For instance, lymphocytes from heat-stressed calves sometimes show lower responses than those from nonheat- stressed calves. This means that a heat-stressed calf may not be able to mount an immune response to infection or vaccination as effectively as a non-heat-stressed calf.