Summer Pneumonia in Calves

Respiratory disease can affect calves of any age. Most of the bacterial pathogens that cause pneumonia are already present in the calf’s upper respiratory tract. They become a problem in the lungs only when immune defenses are compromised, such as by viral infections or stress.

Dr. Eugene Janzen, Assistant Dean, Veterinary Medicine, University of Calgary (Alberta) says some ranches have considerable respiratory disease in baby calves. “When many people calved in January, February and March, putting calving cows through the barn so calves didn’t freeze their ears, calves often picked up pathogens from the confinement/contamination,” he says. But going to later calving, outdoors, hasn’t completely resolved calfhood respiratory problems; some ranches are seeing “summer pneumonia” in young calves.

Studies have looked at this problem in groups of cattle on community pastures. Often these herds have more trouble on dry years, when conditions are dusty when gathering and working cattle. Dust can irritate the respiratory tract, making animals more susceptible to problems.

“When calves inhale dust, the first line of defense may be overwhelmed. If the inside of the nostrils and upper respiratory tract gets clogged with dust, bacteria are not as readily exposed to nasal secretions which tend to kill them or flush them out. If bacteria cling to dust particles, they can also be sucked down into the lungs,” says Janzen. Dust and irritation inhibit normal action of cilia–tiny hair-like structures that line the windpipe, moving in wave-like motions, continually moving mucus, dust and foreign material up out of the respiratory tract to be coughed out.

“If the cowboys had a bad year for dust they were treating more calves for pneumonia. Out of this experience a protocol for communal grazing systems was developed. If ranchers were planning to bring calves to those pastures, they were asked to vaccinate for certain diseases,” Janzen explains.

“They initiated definitive protocols. That strategy worked fairly well in western Canada’s community pasture system because with a formal governance structure, the vaccination protocol was strongly encouraged,” says Janzen.

Here in the U.S. there are also studies on summer pneumonia. Dr. Amelia Woolums, Professor of Large Animal Medicine, University of Georgia, has been working with other researchers looking at pneumonia in pre-weaned beef calves. “There is very little in the scientific literature about risk factors for this disease, compared to feedlot pneumonia. We are trying to understand why some ranches and farms have a problem year after year, and others don’t,” she says.

She helped with a case-control study in the Dakotas and Nebraska. “We enlisted herds that had summer pneumonia, and randomly selected other herds (from the same veterinary practice) that had not had summer pneumonia. We looked at herds that had to treat at least 5% of their pre-weaning calves, and compared them with herds that treated less than half a percent of their calves,” says Woolums.

People tend to think of respiratory disease as stress-related, but most of these calves out on pasture or range are not experiencing stress that time of year unless it’s an unusual weather situation. On some operations ranchers move cattle periodically for rotational intensive grazing, or there may be sub-populations brought together for branding, or for AI programs.

“Mingling cattle from different sources is a risk factor for feedlot BRD, but we don’t know if mingling young calves from different sub-populations on the same ranch can also increase risks for respiratory disease,” says Woolums. When cattle on range are moved several times during summer to new pastures there might be stress if it’s hot, dusty or a long drive, but for cattle that aren’t being moved or handled, we don’t know what might predispose these calves to respiratory disease.

“In a mail survey of producers, we looked at summer pneumonia in 2 ways–whether or not they saw any calves with respiratory disease, and the proportion of calves that they treated for pneumonia. Some things were associated with whether they saw respiratory disease, and different things associated with the proportion of calves treated for respiratory disease. For example, if a farm had calf diarrhea they were more likely to also see calves with respiratory disease. If a farm did AI, they were more likely to treat a larger proportion of their calves,” says Woolums. Those calves may have experienced stress, being gathered and sorted away from their mothers for a short time.

Depending on the conditions–stressful handling, hot or inclement weather, or dusty corrals–there might be factors that make them more vulnerable. “It’s also possible that when calves are sorted away from their mothers and grouped together they have more opportunity to spread respiratory viruses or bacteria among themselves,” she says.

Age of calves can also be a factor–whether they are still protected by colostrum antibodies, or whether a calf received adequate colostrum to begin with. “Some factors may be more important risks on some operations and other factors might be more important on other operations,” she explains.

Usually these calves are in a healthy environment, with very little crowding or contamination. There are still cases of respiratory disease, however, and we don’t know what triggers them. Some producers have started vaccinating calves at spring turn-out and think it helps. Veterinarians in some regions recommend vaccinations, and it may help, depending on age of the calves at that time, and products used. Success may depend on whether calves are old enough their immune systems would respond to vaccination, since maternal antibodies from colostrum may interfere, in certain cases.

“There is some research that supports the thinking that calves 60 to 90 days of age can respond to vaccination. In some instances they do, and sometimes they don’t, depending on different variables,” says Woolums. At any rate, adding a respiratory vaccine to calves’ vaccination protocol at branding age seems to help, on some farms and ranches, reducing the incidence of summer pneumonia.