Pneumonia can affect calves of any age. Most of the bacterial pathogens that cause pneumonia are always present in the calf’s upper respiratory tract. They become a problem in the lungs when immune defenses are compromised, such as by viral infections or stress. One of the frustrating respiratory infections in nursing-age calves is called summer pneumonia.

“Preweaning pneumonia in beef calves is a condition we’re still trying to understand,” says Russ Daly, extension veterinarian and professor at South Dakota State University. Identifying risk factors has been frustrating.

Daly was part of a multistate case-control study in 2012-2013, looking at herds that experienced a significant amount of preweaning pneumonia compared with nearby herds that had not experienced problems. He has continued to study this problem.

“There’s not much new knowledge, but we’ve reinforced some of the things we discovered earlier,” he shares. “Different ages of calves probably have different risk factors. Calves only 1 or 2 months old may not have had good enough (or adequate amount of) colostrum to protect them from early infections.”

Older calves on pasture with their mothers have a normal drop in colostral antibodies, he says. “This may make the whole group more susceptible to pneumonia at once, and there may be other factors we are not aware of.”

“Most cases of pneumonia are bacterial by the time we see them. Primary viral infections like BRSV or bovine respiratory coronavirus simply set up those calves for a bacterial infection.” — Russ Daly

What calves have had — or not had — in terms of vaccines can make a difference in when calves break with pneumonia and its severity.

Every ranch is different. Some producers never see calf pneumonia; others see cases sporadically and not every year. It is hard to identify herds that might have problems.

Large groups, when they all lose their maternal antibodies at once, may see more cases — with more possibility for calves to be colonized with pathogens, Daly says. “We sometimes see more preweaning pneumonia in the better-managed herds, on farms and ranches that do a really good job with vaccinating and looking after their calves, detecting and treating the sick ones.”

Daly admits that’s counterintuitive.

“You’d think producers who don’t vaccinate or pay close attention to their cattle on pasture would have more problems; but, that’s not always the case,” he continues. “It may be that in some of the intensively managed herds, the producers are detecting problems because they are examining their animals more often or more closely. In other herds the sick ones might not be detected, possibly to recover on their own without treatment.”