Livestock Management RANCHING
BRSV: 6 Hours F rom First Sign to Death By David Bechtol, D.V.M.
B
OVINE RESPIRATORY SYNCYTIAL VIRUS (BRSV) PRIMARILY causes a lower respiratory tract infection but can set the stage for fatal bacterial pneumonia
of cattle. BRSV is a virus that replicates in nasal epithelium
before dispersing throughout the upper and lower re- spiratory tract. It has been implicated as a predisposing factor in
fi brinous pneumonia and a cause of interstitial pneu- monia. In cases of interstitial pneumonia, in areas of the lung the air sacs expand to bursting and coalesce into 1 large sac. Oxygen is trapped inside the large sac, which has less blood fl ow to it than each small air sac. The calf eventually will asphyxiate and die. BRSV affects mostly young cattle from 2 to 10 months
of age, but can affect yearling and adult cattle. It appears like many other bovine respiratory dis-
eases (BRD), manifesting in a fever often higher than 104 degrees Fahrenheit, depression, decreased feed intake, increased respiratory rate, a harsh cough and a thick nasal discharge. My experience with BRSV has shown fl uid-fi lled,
swollen lungs with nasal discharge but no pinkeye (conjunctivitis) that is frequently seen in infectious bovine rhinotracheitis (IBR). Shortness of breath with open-mouth breathing can become pronounced in the later stages of the disease, as well as secondary bacte- rial infection, increasing the severity. This disease can run its course in less than 6 hours
from fi rst clinical signs to death of the animal. Gross lesions often seen by the veterinarian on nec-
ropsy include a diffuse interstitial pneumonia along with emphysema and fl uid accumulation in the lungs. Secondary bacterial pneumonia is often present as well caused by bacteria not usually associated with acute bacterial pneumonia. A true diagnosis of BRSV requires laboratory con-
fi rmation. This virus is diffi cult to detect because it does not tolerate transport to the lab well. Work with your veterinarian to collect and test tissue samples to confi rm a diagnosis. BRSV often starts with comingling of calves at wean-
ing or at the feedyard. Clinical signs tend to show up 7 to 10 days after exposure, which can be by nose-to-nose
54 The Cattleman May 2014
contact with other sick calves, or through the air; however, I have seen the worst breaks at 21 days after arrival into a feedlot. The number of
calves becoming sick can be very high in an exposed herd, and the episode of disease may have up to 14 to 30 days duration. Due to lack of response of treatment, mortality can be signifi cant, too, possibly up to 20 percent of the group. There is no specifi c anti-BRSV therapy; therefore,
treatment is limited to antibacterial therapy for sec- ondary bacterial infections and supportive treatment. Vaccination is the primary means for control. Modi-
fi ed live virus vaccines have a better track record than killed vaccines. A recently introduced intranasal vac- cine appears to give the best protection from this dis- ease and may be given to calves older than 8 weeks of age. Studies have noted an association between high BRSV serum antibody titers on arrival at the feedlot and a reduced risk of subsequent respiratory disease. The best way to protect vulnerable calves from this
disease appears to be vaccinating early and often, be- cause calves as young as 6 weeks of age respond well but protective titers tend to last only a few months. BRSV also seems to be more of a warmer weather
disease, exhibiting itself often as a sudden death in the warmer months of the year, particularly in pre-weaned calves at 2 to 6 months of age. Yearling feedyard cattle also seem to be more sus-
ceptible during the warmer weather. This can be a diffi cult disease to control without proper prevention. Editor’s note: David T. Bechtol, D.V.M., of Palo Duro
Consultation, Research and Feedlot, with the help and support of other colleagues, and Merck Animal Health provide a quick reference sheet on what to watch for and provide to your beef cattle herd during your 2014 calendar of events.
thecattlemanmagazine.com
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