Pneumonia is the common term for lung infection. In cattle it’s often called shipping fever because it frequently affects calves that have undergone stress of weaning and being shipped to a feedlot.

Stress is a major factor in whether calves get pneumonia—which can appear at any age since most of the bacterial pathogens that cause pneumonia are already present in the calf’s upper respiratory tract. These bacteria only become a problem in the lungs if the calf’s immune defenses are compromised by viral infections or stress, which may enable them to move on down into the lungs. 

Stress may be due to inclement weather, extreme changes in temperature, a long truck haul, overcrowding in a dirty environment, etc. Nutritional deficiencies such as lack of an important mineral like copper or selenium may impair the immune system. 

Respiratory infection in young calves has been called “summer pneumonia” and the cause is not easy to determine; cases can appear during good conditions when we don’t think of these calves as stressed. In some cases, calves get sick out on summer pasture. 

This is an erratic disease, according to Dr. Chris Chase, Department of Veterinary and Biomedical Sciences, South Dakota State University. A producer might see some sick calves one year and no problems the next year. We often don’t know what the difference might be, and sometimes cases are hard to diagnose.

There might be viruses involved, like bovine respiratory syncytial virus (BRSV), or bovine coronavirus. “There are some pathogens that we might find if we are looking for them, but often in a cow-calf operation by the time we examine the sick calf or get a sample to send for testing, it may be too late to find the pathogen,” Chase said. 

Two age groups

Calf pneumonia tends to occur 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. The younger calves may be vulnerable to pneumonia if they didn’t receive adequate colostrum.

Some producers calve their cows in barns and small pens in late winter or very early spring, and these situations may create exposure to more pathogens than if they were out in big pastures. Confinement and contamination can be major risk factors in very young calves.

Older calves, on pasture, may be vulnerable when their passive (temporary) immunity from colostrum diminishes. When producers have problems with pneumonia the veterinarian generally looks at age of the calves, and which risk factors may have been present prior to them getting sick.

Risks vary from farm to farm. One risk might be gathering pairs for AI synchronization programs, when calves are stressed while temporarily separated from their mothers and in close confinement with other calves. A year with bad weather, or a hot, dry, dusty period in late summer may put calves at risk.  Dust can clog the natural defenses of windpipe and lungs, making the calf more vulnerable to infections.

Producers vaccinate

Some producers vaccinate calves at branding time to try to prevent summer pneumonia and sometimes it seems to help. 

“Use of vaccination as a preventative has been frustrating, however, because the major bacterial pathogens are always present. In calves with summer pneumonia we often see Mycoplasma bovis and Pasteurella multocida but these are both very common in the upper respiratory tract and in the nose, even in healthy animals,” said Chase. 

If the calf gets a viral infection that damages the lining of the windpipe, or suffers from environmental stress, those factors may open the way for the resident bacteria to get farther down into the airways and enter the lungs.

“Getting an accurate diagnosis is difficult, and not knowing the actual pathogen that’s causing illness, we can’t effectively use an intranasal vaccine,” he said.  If the producer uses a vaccine that just has IBR and PI3 in it, this may not be protective.

“If a producer has had problems in the past with BRSV in calves (as determined by samples and necropsies) it might make sense to use a vaccine containing BRSV. We did some research and published a paper last year, looking at using an injectable vaccine (as opposed to an intranasal vaccine), and were able to show that calves could gain mucosal immunity from an injectable vaccine. It depends upon the adjuvant in the vaccine, but the key is having an accurate diagnosis,” he said. 

The only way you can select an appropriate vaccine (if there is one) is to know which pathogens are causing the pneumonia. Producers can use intranasal or injected vaccines, but it needs to be the right injectable product. 

Environmental factors

Environmental factors play a huge role (stress of weather, etc.) and in summer heat young calves need to stay hydrated. “When we look at respiratory disease in highly stressed animals or dairy calves, the ones that have adequate water always have fewer cases of respiratory disease,” Chase said.

If calves can’t get to water, or if the water is poor quality, they won’t drink enough.  Dehydration can have an adverse effect on their immune system. “With the immune system, everything must be able to keep moving—whether it’s mucus in the upper respiratory tract that has to clear things out (dust, pathogens) or fluid in other body systems.”  If the animal is dehydrated, nothing works optimally.

In hot weather some of the ponds and creeks that cattle drink from may dry up or have poor water quality. “In our part of the country it’s stock ponds/dams,” said Chase. Range cattle often have to travel long distances to water, and if they are drinking from troughs that get low on water, the calves may not be able to reach it. 

“If there are issues with water—either quantity or quality (which affects how much the calves are going to drink)--we often see an increase in respiratory disease. This can be an issue in dairy calves as well, if they don’t have adequate water in hot weather.”

Vaccination is often looked upon as the solution to problems, but if people start to think they can depend on a vaccine they may overlook other management protocols they need to be doing. “Vaccines are not the entire solution,” he said. 

“Some of the common pathogens are bacteria but there may also be a viral component like BRSV or a coronavirus—especially if pneumonia pops up across the whole group. If it’s just an odd animal here and there, it’s more likely to be bacterial—and those cases tend to be more chronic and harder to clear up,” he explains.

[Heather Smith Thomas writes from Salmon, Idaho]