Heat stress in dairy calves – inside and out

Eric Weaver for Progressive Dairyman

Producers know the consequences when temperatures reach 90°F or higher – heat stress-induced morbidity and mortality. Calves cannot regulate internal temperature beyond their thermal neutral zone, which makes them much more sensitive to heat, especially when humidity is high. Imagine wearing a leather coat in the summer.

Calves in heat stress conditions experience rapid dehydration, elevated body temperature, increased energy requirements and reduced food intake. The strain of maintaining normal body functions decreases the calf’s growth rate and your bottom line.

New heat stress research in humans has demonstrated a relationship among heat stress, gut permeability and the immune response. When the body temperature rises, so does gut permeability. Bacteria, viruses and antigens can pass through the compromised gut barrier and stimulate the immune system. It is more likely stressed humans will get sick.

In calves, the stimulated immune response leads to an increased likelihood of heat stroke, dehydration, failure of passive transfer and depressed immune function. Each of these factors has an elevated risk for diarrhea and ultimately death.

Research data supports the use of immunoglobulin and other proteins to decrease the negative physical effects of heat stress, including decreasing mortality rates by as much as 50 percent during peak summer temperatures. Up to 50 percent of mortality can be attributed to heat stress under those conditions (see Figure 1). Know the signs of heat stress:

•Reduced movement

•Faster breathing rates

•Open-mouthed panting

•Decreased feed intake

•Increased water consumption

•Desire for more shade

Stressed calves require more work and can stress you out, too! Mitigate the effects by taking preventive measures. Housing adjustments and other changes to lower the ambient temperature will help prevent elevated calf body temperature.

Move the calves out of direct sunlight and provide supplemental shade. Move hutches into the shade or cover with a cloth to block sunlight.

Make nutritional changes. Changes, such as the introduction of immunoglobulin, can reduce diarrhea and gut permeability and increase feed intake. Research data supports the use of immunoglobulin and other proteins to decrease the negative physical effects of heat stress.

Supply ample amounts of cool, fresh water to address dehydration issues. Water is extremely important because it not only helps with dehydration it also helps cool the calf internally. Be prepared. A heat-stressed calf can drink up to 6 gallons of water daily. An extra water feeding may be necessary. And ensure calves have fresh water during the cooler night when calves consume more feed and consequently drink more water.

Mist calves. Use sprinklers to supplement natural sweating and increase evaporation.

Use sand or other bedding that does not insulate the calf.

Perform stressful activities early in the morning. Perform stressful events like handling or vaccinations before 10 a.m.

Increase airflow and air exchange. Take advantage of natural ventilation and open hutch vents and barn doors. If you have them, turn on fans. Airflow will increase the rate of evaporation and dissipate the heat. PD

References omitted but are available upon request.