BRSV in Cattle
contributed article by Dr. Vince Collison, Collison Embryo and Veterinary Services,
Rockwell City, Iowa
One of the more common viral components of bovine respiratory disease we’ve encountered in the Midwest is Bovine Respiratory Syncytial Virus (BRSV). This virus is usually seen in calves anytime from 2-months of age through 9 to 10 months. It seems that this virus is common in Iowa during the summer months during times of excess heat and humidity.
It also is sometimes seen in feeder cattle as they start to get worked up on feed and are consuming more concentrates in their diet. Probably one of the more common situations where I’ve seen calves break with BRSV, is after calves return home from the state fair. Most times this is in younger spring born calves that are going out to show for the first time. Probably the combination of heat, exposure to cattle from multiple herds, waning maternal antibodies, low immunity for BRSV, and crowded conditions at tie outs make for perfect conditions for exposure.
Preconditioning Prior to Weaning
This virus is one of the main reasons we recommend preconditioning calves prior to weaning. The cases of BRSV I’ve seen in recently weaned calves that are not vaccinated are some of the toughest cases to treat and get resolved. Since it is a virus, BRSV will spread rapidly in a group and can be very non-responsive to antibiotic treatments.
Clinical signs include fevers that will go as high as 107 degrees Fahrenheit. This virus will cause severe inflammation in the bronchioles and alveoli tissue resulting in blockage of airways that causes a severe expiratory restriction in the lungs. This can result in air getting trapped in the lungs to the point of causing gas pockets to accumulate in the upper lobes of the lungs.
In addition, this inflammation damages the epithelium in the lung lining making the calf very prone to secondary bacterial infections such as Histophilus, Mycoplasma, and M. hemolytica. Also, BRSV is probably one of the tougher infections to vaccinate against, so this is the primary reason we recommend a booster of the 5-way viral vaccines 2 to 3 weeks after the initial vaccination. So, it is best to get calves preconditioned along with a booster prior to weaning. If the booster cannot get done prior to weaning, at least try to give a 5-way booster on the day they are weaned.
Vaccination Timing
The other time we will see BRSV is in calves on pasture around late June to early July. For herds that experience this problem we like to get calves vaccinated as they go out to grass. These calves will also experience high fevers and often have open mouth breathing and a hard time moving air in and out of their lungs. Dogma says not to vaccinate this young because of the interference of the vaccination from maternal antibodies. In these herds, we have found that the only way to control BRSV this young is to go ahead and vaccinate with a modified live 5-way vaccine. It has seemed to work even in the face of maternal antibodies in these herds.
In feedlots, BRSV can often break at about 30 days into the feedyard. The virus likes an acidic environment and as cattle get worked up on feed and experience some acidosis, it seems that cattle can be more prone to BRSV. In cases like this, it is probably best to back them off on grain until the cattle can be straightened out.
Diagnosing BRSV
The diagnosis of BRSV is usually done off clinical signs and body temperatures. The best way we have found to diagnose BRSV through laboratory means is by running a PCR test on lung tissue from a posted calf. It is hard to isolate the virus, but the PCR test is good at picking up DNA evidence in the tissue.
If there are no calves to post, a good way to get a sample is from a tracheal wash. This procedure is fairly easy to do with the right equipment and multiple calves can be sampled. Tracheal wash samples can be used for PCR testing and also bacterial culture. Blood samples can also be drawn for antibodies for BRSV, but we have relied more on the PCR testing and bacterial culturing as these will give results quickly and are far easier to interpret.
Treating BRSV
When we treat BRSV, we rely on the usually used antibiotics that are approved for BRD in cattle along with supportive care. Anti-inflammatories are very important due to the increased immune response stimulated by BRSV. We will use NSAIDS such as Flunixin, but will also use a steroid such as dexamethasone. Dexamethasone is a potent anti-inflammatory that works quite well in cases of BRSV to open the airways. One thing about dexamethasone is that while suppressing the immune system is helpful for BRSV, it can be counter indicated in cases of IBR virus. It is probably best to work with your herd veterinarian to get a diagnosis before treating with steroids, so as not to do more harm than good.
BRSV is one of the more common viruses seen in cases of Bovine Respiratory Disease. Vaccination for BRSV with a follow up booster 2 to 3 weeks later can work quite well in controlling the disease. As always, work with your herd veterinarian to plan a vaccination program that will work best in your situation for control.
learn more www.collisonembryoservices.com
Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC
in Rockwell City, Iowa.
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