Year in and year out, diseases of the respiratory system are a major cause of illness and death in cattle from six weeks to two years of age, says Dr. Donald Montgomery, director of the Wyoming State Veterinary Laboratory. Sadly, this is as true today as it was 30 years ago despite development of new and improved vaccines, new broad spectrum antibiotics, and increased fundamental knowledge as to the cause of disease.
Montgomery says he does not have the answers for why this happens, but offers these ideas for managing BRD.
* The bovine respiratory disease complex (BRD, shipping fever) is a multifactorial process. There are many variables that come together to cause disease. No two scenarios are exactly alike but they often culminate in severe and fatal bacterial pneumonia.
* The variables, viruses, and bacteria are the same whether or not the cattle are pastured or confined in a feedlot; the feedlot environment simply magnifies the different participants.
* Viruses are an important component of BRD but are not necessarily present in all outbreaks of respiratory disease. The major viruses are IBR (bovine herpesvirus type 1), parainfluenzavirus-3, respiratory syncytial virus, and bovine virus diarrhea.
* BVD is not generally considered a primary respiratory pathogen in the sense of the other viruses just mentioned; it is more likely responsible for crippling the immune system.
* The industry is making pretty good strides at eliminating calves persistently infected with BVD virus but it is still out there and persistent infected calfs serve as a source of infection for herd mates.
* Bacterial pneumonia is the real killer in shipping fever. These names are also very familiar to you; the most important being Mannheimia hemolytica, Pasteurella multocida, Histophilus somni (formerly Hemophilus somnus), and Mycoplasma spp. (bovis).
* There are over 60 different vaccines marketed as an aid in the prevention of BRD. I can appreciate why the choice of vaccines for a herd health program can be confusing.
* The best vaccine on the market is of little benefit if mishandled, misused, or given at the wrong time.
* Like vaccines, several new antibiotics have been marketed in recent years. These antibiotics are efficacious against a broad range of bacterial pathogens.
* Use of these powerful antibiotics is often of little benefit if given too late in the course of disease when damage to the lung is far advanced. Importantly, a trend of bacterial pathogen’s developing antibiotic resistance noted 10 to 15 years ago is reversing itself. Montgomery says he would like to believe that this is due to the more judicious use of these drugs by the cattle industry, and offers his congratulations.
* Performing diagnostic tests for cases of BRD is the only way for producers, practicing veterinarians, and diagnostic laboratory personnel to learn.
* Is the benefit worth the cost? This is something the producer will need to answer for themselves.
* It is imperative that diagnostics for viral infection be done early in the course of clinical disease; many viruses such as PI-3 and RSV are present only during the early stages, if you wait until an animal has died the virus may no longer be recovered.
* There is no substitute for isolation of the virus. For this, deep nasal or pharyngeal (throat) swabs are samples of choice. It is important to get the swabs sopping wet with secretions and send the swabs chilled in a sterile container.
* The downside of virus isolation is the turn-around time that can be up to 2 or 3 weeks.
* Another different method of testing is serology. Blood samples need to be taken at the onset of clinical illness and another sample 10 to 14 days later.
* The two most common bacteria, M. hemolytica and P. multocida are the easiest to differentiate.
* Mannhemia hemolytica causes an acute, rapidly progressing,
* Fulminating pneumonia. The affected animals are obviously very sick and many cases will die from 3 to 7 days after the onset of illness.
* If treatment is delayed, even if the animals recover, there will be considerable residual lung damage. At the opposite extreme, the pneumonia caused by P. multocida tends to be insidious and develops more slowly. It is difficult for these animals to be identified as clinically ill. Diagnostic labs and specifically pathologists are really not in a position to make treatment decisions or recommendations.
* The three rules of antibiotic therapy remain valid today, even with the newer antibiotics that have come on the market: Proper early diagnosis;
* Selection of an appropriate antibiotic and proper dosage, route, and treatment schedule.
* Another recommendation is that effective treatment should be accomplished with as little stress to the cattle as your management capabilities will allow.
* When the situation becomes sufficiently dire, metaphylaxis or mass medication may be the best or only option but make sure there are adequate, justifiable reasons for the added stress and expense of treating the entire herd.
Source: www.cattlenetwork.com
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