Bovine Respiratory Syncytial Virus in Cows: Symptoms and Care

Bovine respiratory syncytial virus, or BRSV, is a contagious viral infection of the respiratory tract in cattle. It is considered an important cause of bovine respiratory disease and has a strong tendency to affect the lower airways and lungs, not only the nose and throat. Merck Veterinary Manual notes that BRSV occurs most often in young beef and dairy cattle under 6 months of age, although adult cattle can also be affected during herd outbreaks.

This virus matters because it can act as a primary cause of viral pneumonia and also set the stage for secondary bacterial pneumonia. In practical terms, that means a calf may start with fever, cough, and faster breathing, then worsen as bacteria such as Mannheimia haemolytica or Pasteurella multocida take advantage of damaged lung tissue.

Outbreaks can spread quickly in groups of calves, especially where animals are recently transported, mixed, stressed, or housed in poorly ventilated spaces. Morbidity can be high in affected groups, and some animals develop severe breathing distress or fatal interstitial pneumonia. Even when many cattle recover, the outbreak can still lead to treatment costs, slower growth, and production losses.

Because several respiratory diseases in cattle look similar, your vet usually treats BRSV as part of a bigger respiratory picture rather than as a stand-alone problem. That is why diagnosis, treatment planning, and prevention are usually done at the herd level as well as for the individual sick animal.

BRSV is caused by an RNA virus in the pneumovirus group of the Paramyxovirus family. It spreads between cattle and is found worldwide. The virus is considered common in cattle populations, so many herds are exposed at some point.

Transmission is usually linked to close contact, respiratory secretions, and management conditions that help respiratory pathogens move through a group. Risk tends to rise when calves are weaned, transported, commingled, crowded, exposed to weather swings, or housed with poor ventilation. Stress does not create the virus, but it can make outbreaks more likely and more severe.

One reason BRSV is so important is that it can damage the lower respiratory tract and make it easier for bacteria to invade. That is why BRSV is often discussed as part of the bovine respiratory disease complex rather than as an isolated infection. Cornell has reported cases where BRSV was confirmed by PCR while bacterial pathogens such as Mannheimia haemolytica and Pasteurella multocida were also present.

Maternal antibodies may reduce how sick a calf becomes, but they do not fully prevent infection. Initial exposure is often the most severe. Later exposures may be milder or even subclinical, which can make herd-level control more challenging.

Your vet usually starts with the basics: herd history, age group affected, recent stressors, vaccination history, temperature, breathing pattern, lung sounds, and how many animals are sick. Because BRSV looks similar to other causes of calf pneumonia, diagnosis is often presumptive at first and then confirmed with testing when needed.

According to Merck Veterinary Manual, PCR is a useful and rapid method for detecting BRSV. Cornell's Animal Health Diagnostic Center offers a bovine viral respiratory PCR panel that includes BRSV along with BVD, bovine herpesvirus 1, parainfluenza-3 virus, and bovine coronavirus. Appropriate samples can include nasal or nasopharyngeal swabs, fresh lung tissue, transtracheal wash fluid, or bronchoalveolar lavage fluid.

Your vet may also recommend bacterial culture or additional testing if secondary pneumonia is suspected. Serology can help in some outbreaks, especially paired acute and convalescent samples, but interpretation can be tricky because antibody levels may rise quickly and calves with maternal antibodies may not show a clear serologic pattern.

In severe cases or deaths, necropsy and lung tissue testing can be especially helpful. That can confirm whether BRSV is the main driver, whether bacterial pneumonia is also present, and whether the herd needs changes in treatment or prevention strategy.

Prevention usually works best when it combines vaccination, biosecurity, and management. Merck Veterinary Manual states that both killed and modified-live BRSV vaccines are available in injectable and intranasal forms. Your vet can help decide which option fits your herd, calf age, maternal antibody status, and timing around weaning, transport, or commingling.

Timing matters. Calves are often most vulnerable when they are stressed, mixed with new animals, or moved into new housing. Building a herd plan that vaccinates before predictable stress events may reduce losses, even though real-world vaccine performance can vary from farm to farm.

Management changes are also important. Good ventilation, lower stocking density, dry bedding, reduced dust, clean water access, and minimizing abrupt stressors all help lower respiratory disease pressure. Quarantine and observation of incoming cattle can also reduce the chance of introducing new respiratory pathogens into the group.

If an outbreak happens, early separation of sick animals, prompt veterinary assessment, and review of treatment and vaccination protocols can help limit spread and reduce losses. Because BRSV often overlaps with other respiratory pathogens, prevention is strongest when your vet builds a whole-herd respiratory program, not a virus-only plan.