Heat stress in weaned calves and how to manage it

Proper care of calves in the heat is essential for animal HEALTH

Peter Witty, an independent Canadian livestock consultant, writes more about this in his article. 

“Heat stress begins to harm dairy calves as early as around 22°C and at least 60% relative humidity. At this humidity level, I have seen many calves become restless, reduce their feed intake and increase their water intake significantly.

As the temperature rises (combined with increased humidity), most of them sooner or later begin to breathe quickly and heavily, and their immune systems literally turn off. At the same time, their overall metabolism shifts from growth to solely maintaining normal body temperature. Therefore, our task is to ensure that the calves are well maintained so that they remain healthy and continue to grow.

Weaned calves die from heat stress related diseases or high fevers. Basically, they are killed by severe dehydration caused by the loss of more than 10 percent of their weight in body fluids.

This significant loss of body fluid weight is primarily composed of cellular/tissue water and dissolved electrolytes. We often see this type of dehydration in sick calves dying from pathogenic or nutritional damage, however significant fluid loss in heat stressed calves does not come from the intestines, but rather from their lungs and urine.

On my recent tour of the barn, I put my hand on a panting calf with sunken eyes (a sign of severe dehydration), and within minutes my hand was wet. This is because the calf exhales large amounts of water in the form of steam into the air.

This pulmonary water loss is one of the many reasons why calves double or triple their water intake in the heat, resulting in frequent urination and a dangerous loss of vital electrolytes sodium, chloride and potassium.

Electrolyte supplements are often used to rescue calves from heat stress, but it is important to ensure that their water requirements (10 liters is normal, 20 liters in hot weather) are first met by supplementation with the whole MILK or substitute being fed.

Case in point: A calf study by feed supplier APC Inc. measured the water intake of 120 newborn Holstein bulls. The researchers offered each calf 4.0 liters of "extra water" daily in addition to 6.0 liters of milk replacer. The results showed that the water intake of the calves increased significantly when the outside temperature increased from 20 to 25°C, which was comparatively greater than when the temperature increased from 5 to 10°C.

I know many breeders who follow the "extra water" recommendations and add a scoop of commercial electrolytes to the same "extra water" buckets.

These salts are usually less concentrated than "healing" electrolytes and are given as a preventive measure.

In addition to additional watering, calves should be provided with a shady place with fresh air, sanitation and control of flies.”