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BRSV (Bovine Respiratory Syncytial Virus) is a deadly viral cause of pneumonia

Health: Know the signs and what actions you should take if you suspect the virus

I am sure most cattlemen have had the odd diagnosis of BRSV in their herds over the years, either individual animals or outbreaks, generally in cattle under one year of age.

BRSV is suspected with pneumonias that do not respond to antibiotics or produce lots of fluids and frothing as well as runny eyes. Temperatures can be very high and these cases are often acute. In the feedlot they often appear as sudden deaths with the post-mortem diagnosis providing the final answer.

On the post-mortem the veterinarian will often find various levels of edema and emphysema throughout the entire lung. Once we see how quickly it comes on and the damage the lungs undergo it is not surprising that mortality is so high.

Usually it is more evident in the fall with the stress of weaning or during times when temperatures flit below or above freezing leading to pulmonary edema (fluid in the lungs), thus providing a great medium for the virus to grow. Stress from weather changes or poor ventilation can also bring on BRSV. Morbidity can range up to 10 per cent to 20 per cent but generally only a few cases are seen at one time.

The vast majority of our vaccination programs include BRSV as one of the key viral components, which means most calves should get an initial vaccination at two to three months of age followed by a second dose at or before weaning. This is included in the classical preconditioning shots.

Cows are often boostered annually in a viral program that also includes IBR, BVD, and PI3. As with all vaccination programs increased stress or exposure to the organism can still result in disease. Five-way vaccines also contain BRSV, so cows on this program should pass some colostral immunity off to the calves.

In these cases where the herd is previously vaccinated, especially with BRSV, I always feel there is a greater likelihood of saving the calf.

The BRSV virus is very sensitive so even though one suspects it as a cause of sickness, a veterinarian may be unable to get a positive confirmation from lab tests. Experienced veterinarians will make their diagnosis based on clinical signs, and gross autopsy findings, if they do a post-mortem. I always say to veterinarians and producers, if it acts and looks like BRSV, there is a very good chance that’s what it is.

Treatment is much more frustrating as we often see some of these cases during the cattle show season when cattle are being watched intently and producers notify us within a few hours of sickness appearing. With BRSV causing damage so quickly, you treat the symptoms with anti-inflammatory drugs to reduce the inflammation and the fever.

I have had success using antihistamines as well as diuretics to try and reduce the fluid in the lungs. Antihistamines help dry out the lungs and make breathing easier. Other than allergic reactions this may be one of the few times veterinarians prescribe antihistamines.

Getting the calves out into a fresh, cool area is also critical. This is difficult to do in dairy calf and veal barns so good ventilation is critical for prevention in housed cattle. Veterinarians will often prescribe antibiotics, as well, more because pneumonia is a definite possibility with damaged lungs.

Initially fluids may need to be given to ward off dehydration. The newer immune stimulants may be another tool your veterinarian may prescribe in the future. One must treat these cattle gently as even the stress of treatment or catching in a chute can push them over the edge. I have found with better vaccination for bacterial pneumonias and antimicrobial therapy, we vastly reduced those types of pneumonia, but the viral ones, especially BRSV, are our nemesis.

I have found that even in recovered cases there has been enough permanent damage that they may do poorly. In commercial cattle I would not recommend keeping them as replacements. Even valuable breeding stock may end up being poor breeders as they don’t grow as well and have trouble keeping weight on.

BRSV can be a costly disease both in terms of the high mortality and the chronics it can create. As with other respiratory diseases keep the vaccinations up to date. Some companies tout a one-shot BRSV but that is a moot point as you always combine it with the other viral vaccines anyway. Minimize stress and worry about ventilation in housed cattle.

I recommend that show cattle get a booster shot a week before show season with either injectable or intranasal vaccines to booster immunity to all types of respiratory disease including BRSV.

I have seen severe cases of BRSV turn around and other cases relapse in a few months resulting in mortality. This is one of the biggest reasons show cattle have lots of air blown over them to minimize heat stress and susceptibility to all types of pneumonia, but BRSV is one of the most difficult to treat.

The advent of many anti-inflammatory drugs has gone a long way to helping you and your veterinarian treat BRSV cases but prevention remains our primary goal.

About the author

Contributor

Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.

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