Lung problems come in all forms in the cattle industry—dust inhalation, flukes, various respiratory complaints, etc. But there are few things more frustrating than pneumonia in otherwise healthy, happy calves.
Pneumonia (infection in the lungs) can affect calves of any age. Most bacterial pathogens that cause pneumonia are already present in the upper respiratory tract. They become a problem in the lungs only when immune defenses are compromised by viral infections or stress. Stress may be due to bad weather, extreme changes in temperature, a long truck haul, overcrowding in a dirty environment, or nutritional stress due to deficiencies of an important mineral like copper or selenium, among many other things.
One of the most frustrating respiratory infections in nursing calves has been called “summer pneumonia.” The cause is not always easy to determine, especially since cases tend to appear in situations when we don’t think of calves as being stressed.
“We don’t have a good handle on what’s happening,” says Russ Daly, DVM, and Extension Veterinarian of South Dakota State University.
“We can understand stress of transport, weaning, dusty corrals, etc., but often this is different.”
He was part of a multi-state case-control study in 2012-2013, looking at herds that experienced significant pre-weaning pneumonia—comparing them with nearby herds (the control animals) that had no problems.
“By using herds in the same location and time frame, we hoped to remove regional and environmental differences. There are sometimes neighboring ranches in which one had problems and the other didn’t, so we were trying to find out if there are differences in how they manage and comingle cattle, move cattle, or administer vaccination programs,” says Daly.
Dr. Amelia Woolums, professor of large animal medicine at the University of Georgia, also worked on this study.
“There is very little in the veterinary scientific literature about risk factors for this disease, compared to feedlot pneumonia. We are trying to understand why some producers have a problem with it and others don’t.”
For this study, researchers looked at herds that had to treat at least 5 percent of their pre-weaning calves. “We compared them with herds that had to treat less than half a percent of their calves,” she says.
“We know a lot more about weaning age and post-weaning respiratory disease in calves and how to prevent and treat it,” says Daly. “If we can minimize stress levels and do a good job of vaccinating, we expect to see fewer problems,” he says.
The frustrating thing about summer pneumonia in younger calves (pre-weaned) is that even though producers think they are reducing stress and providing good vaccination programs, it’s not working to prevent the disease as uniformly as it does for post-weaning respiratory problems.
Risk factors
“We understand the risk factors in older calves, but we don’t generally see those factors when calves are with their mothers on summer pasture, yet some of them get sick. Summer pneumonia tends to be sporadic. It is not something every herd has, or that a herd has every year. The risk factors are still largely unknown,” says Daly.
“We tend to see pneumonia in two different age groups—young calves up to a couple months of age and then later when calves are at pasture and close to weaning age. The risk factors for those two groups are generally different,” he says.
Younger calves have problems if they don’t get adequate colostrum. In some cases, producers calve their cows in barns and small pens while it’s still winter, and sometimes these situations create exposure to more pathogens from calf to calf that wouldn’t be present in big pastures. Confinement and contamination are risk factors in very young calves.
Older calves, out on pasture, may be vulnerable when their passive (temporary) immunity from colostrum has waned.
“When producers have problems, we look at the age of calves affected, what risk factors may have been present prior to them getting sick, etc. We see situations where we suspect contact with older cattle (stockers that may be shedding more respiratory pathogens) could be an issue,” Daly says.
There may be genetic differences; some calves are more (or less) able to mount immune response. “We’re just scratching the surface of that possibility,” he says. We know crossbred cattle have “hybrid vigor” which includes more hardiness and disease resistance. There may also be subtle genetic differences among cattle.
Risk factors may be different from farm to farm or group to group. One risk might be gathering pairs for AI synchronization programs, when calves are separated from their mothers.
“It’s usually a very short period and we wouldn’t think it could be enough stress to affect the calves, but maybe there’s more transmission of bacteria or viruses,” he says. There may be multiple factors, working together.
“There may be some stress on those calves—but also they are in close contact with one another. If a few are shedding a lot of pathogens they may expose the other calves,” Daly explains.
A year with really bad weather, or a hot, dry, dusty period in late summer may put calves at risk. “Dust clogs up the natural defenses of windpipe and lungs, making the calf more vulnerable to infections. We’re still trying to understand weather stresses and how they might play into this. Short stresses like a brief storm are usually not a problem.”
Everyone who has dealt with this disease has ideas about risk factors, but these are just guesses.
“We need to do the research to know which factors are important,” says Woolums. People tend to think of respiratory disease as being stress related, but most of these calves on pasture or range are not obviously experiencing stress that time of year unless it’s an unusual weather situation.
A period of changeable weather such as multiple hot days and cold nights, more than 50-degree swings in temperature from night to day, coupled with dusty conditions, might be a factor.
“Extreme swings in temperature tend to allow pathogens to thrive in the nasal passages. This can affect the way those pathogens colonize in the respiratory system,” says Daly. — Heather Smith Thomas, WLJ correspondent
