18 March 2025

3 minute read

By: Four Star Veterinary Service

North America

All land mammals – including calves — have the ability to produce “reflex tears” to lubricate their eyes.

So, if your calves are shedding tears, don’t cry. Those tears are actually a very helpful component of their physical immunity, according to Dr. Taylor Engle, veterinarian with Four Star Veterinary Service, Chickasaw, Ohio.

“Calves are born with a natural armor, in the form of tears and mucous, that helps protect them from invasive pathogens that could make them sick,” Engle told the audience of the 2024 Dairy Calf and Heifer Association Annual Conference. “It’s when calves become dehydrated, and lose some of that natural protection, that we start to run into problems.”

While dehydration in calves is usually associated with scours or a missed feeding, Engle said mild to moderate dehydration may actually be the root cause of a calf getting sick. He said dehydration stress can reduce or disrupt the immune system’s ability to respond to a disease challenge. That may include enteric pathogens that lead to scours, which in turn makes the dehydration situation even worse.

Engle said the transportation of very young calves throughout the country is becoming a growing trend that does no favors to calves’ hydration status. In addition to disease resistance, inadequate hydration also may affect:

• Vaccine response – When vaccinated with an intranasal vaccine, calves need nasal moisture to properly absorb and process the vaccine. Vaccinating a dehydrated calf is a waste of money and labor, and can cause even more stress on the calf.
• Blood volume – Antibiotic treatments of a sick calf also offer little value, said Engle, if those calves lack sufficient blood volume to transport the drug through the calf’s system.
• Weight gain and stature growth – “Stressed calves spend more time and energy responding to those stressors, which detracts from growth, because calves have limited physiological resources to go around,” noted Engle.

Oral electrolyte therapy can be the first-line defense in restoring hydration and protecting immunity in calves, especially those that have traveled long distances. Engle advised feeding electrolytes to calves immediately before transport and after arrival at their destination. More stressful procedures like vaccinating should be delayed until newly arrived calves have had a chance to recharge and regulate their hydration status.

Engle is also a proponent of training qualified on-farm staff to administer intravenous (IV) fluids. 

“With instruction by the herd veterinarian, calf caretakers can become very adept at delivering IV fluids, which means we can get them into calves faster, versus having to transfer a sick calf to a clinic or wait for the veterinarian to arrive at the farm,” he explained.

Using oral and intravenous fluids as a front-line health defense when calves show mild, initial signs of illness also has merit. 

“We call it the ‘medicine of management’ approach,” shared Engle. “In many cases, if we catch illness symptoms quickly enough, rectifying hydration status is all we need to do to help calves recover.”

That’s an especially important point when considering Engle’s prediction that the on-farm medication toolbox of the future may be shrinking.

“As an industry, I think we’re going to be tasked with doing more with less going forward,” he stated. “Supporting calves with fluids can go a long way toward avoiding the need for other medications.”