Source: Land O’Lakes Animal Milk Products Company
Scorching days and stifling humidity cause dairy producers to worry about the comfort and performance of their lactating cows. But heat stress is an issue of concern for calves, too.
“Research has shown that calves stressed by excessive heat can have reduced immunity and higher stress hormone concentrations,” says Tom Earleywine, PhD, Director of Nutritional Services for Land O’Lakes Animal Milk Products Company. “They also may have diminished dry-matter and water intake. These combined factors create an increased likelihood that calves will get sick with pneumonia, scours or other disease challenges; coupled with a potential reduction in growth and weight gain.”
Heat stress indicators
Earleywine advises watching for signs that calves are heat-stressed, including:
- Panting and open-mouth breathing
- Lethargy and sluggish behavior
- Decrease in appetite
- Dry gums and mucous membranes due to dehydration
As dehydration becomes more severe, calves also may exhibit sunken eyes and an increased pulse rate. The “skin-pinch” test is another method to evaluate dehydration. To perform it, pinch or “tent” a fold of skin at the calf’s neck and observe how many seconds it takes to flatten. In normal calves, it will return to its regular position in less than two seconds. A flattening time of up to four seconds indicates the calf is up to 8% dehydrated. If it takes longer than that, even more serious, and potentially life-threatening, dehydration has set in.
Relieving dehydration with electrolytes
Earleywine says it is important to take action quickly, when the first signs of dehydration appear.
“When calves become dehydrated due to increased respiration and sweating, they don’t just lose water,” he says. “They also experience an upset in equilibrium, because less water is available to carry liquid waste out of the body, and to maintain the fluids-to-solids balance in the large intestine.”
Electrolyte therapy can help restore tissue hydration and metabolic balance in dehydrated calves. In addition to supplemental water, they provide calves with dissolved salts -- and sometimes supplemental energy -- to return calves to normal equilibrium.
Earleywine offers the following tips for successfully feeding electrolytes:
- Start feeding electrolytes at the first sign of dehydration. Even if the weather cools off, the cascade of events in the calf’s system already has begun.
- Continue to feed milk/milk replacer when feeding electrolyte solutions. Very few electrolyte formulations contain enough calories to support maintenance and gain. Even in scouring calves, the nutrients supplied by milk and milk replacer are important for supporting recovery.
- Feed electrolytes separately from milk-based feedings. Never mix electrolyte products directly with milk-based products. This can actually draw water into the intestines, increasing dehydration and prolonging scours. Calves lose a large amount of water when scouring, therefore the additional water provided by the electrolyte solution is desperately needed.
- Calculate the volume of electrolytes fed based on level of dehydration. An easy formula is to multiply the weight of the calf, in kilograms, times the level of dehydration, to determine the number of liters of electrolyte that should be fed. Example: a 50-kg. (110-lb.) calf that is 8% dehydrated would require 4 L (about 4.25 quarts) of supplemental electrolyte solution per day, in addition to its regular feedings. Calves above 8% dehydration should also be given appropriate intravenous (I.V.) or subcutaneous electrolytes.
- Feed electrolytes at or just above body temperature. Even in hot weather, feeding warm electrolytes will aid in consumption and absorption by the calf’s system.
- Tube-feed electrolytes with an esophageal feeder if necessary. Don’t wait until the calf is “ready” to drink electrolyte supplements. If they already are to the stage of dehydration at which they are not readily suckling, immediate support from electrolytes is critical.
- Read product labels carefully. Electrolyte products can vary in the manner they should be reconstituted and fed. Always read the label and follow the manufacturer’s instructions. Feeding the solution too concentrated can make problems worse.
- Don’t be afraid to use I.V. or subcutaneous electrolytes. If calves are severely dehydrated they need this as well as oral electrolytes. Work with your calf specialist or veterinarian to determine when to use I.V. or subcutaneous electrolytes, what to use, and how much.
Keeping heat stress in check
Earleywine recommends taking as many steps as possible to reduce the impact of heat stress on calves. These may include feeding fresh, clean, free-choice water at all times; increasing air movement around calves; providing shade from direct sunlight; using sand bedding; providing drip cooling or misters with fans; and performing stressful events such as vaccination, dehorning and pen moves in the cool of the early morning.
“It’s true that calves produce less metabolic heat than adult cows, and have a greater relative body surface area to dissipate heat,” says Earleywine. “But when they do begin to suffer the effects of heat stress and lose fluids, their decline also is more rapid. Every animal in the herd needs extra attention in hot weather, including the calves.”