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, PhD, Attica Veterinary Associates, Attica, N.Y., says heat stress can cause many negative effects on young calves.
If calves are born during a period of heat stress, Lance Baumgard, PhD, Iowa State University, says shade, plenty of colostrum and clean drinking water are important. “Heat-stressed animals have a compromised intestinal function,” he notes. Fortunately, he says, it is more difficult to heat stress smaller animals such as calves vs. lactating cows, primarily because the method of dissipating heat is largely dependent upon the surface area to mass ratio which is quite large in a neonatal calf.
But when calves are heat-stressed, primary negative effects include 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 four quarts each feeding of powder mixed at 15% solids (2.5 lbs. daily) between 3 and 5 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.”
Leadley says during times of heat stress he would try to coax calves into eating more at night by giving them fresh grain and fresh water at 6 p.m. “This worked somewhat but that long period of inactivity between 11 a.m. and 5 p.m. just hammered starter intakes.” And, if dry matter intakes were down, so was their rate of growth.
Whether in a hutch or a pasture, all ages of dairy calves and heifers can suffer from heat stress. 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.”
Heat stress impacts immunity
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 preweaned calf, notes says Amelia Woolums, DVM, MVSc, Dipl. ACVIM, Dipl. ACVM, University of Georgia.