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Watch for newer respiratory pathogens

Animal Health: One is a virus, the other a bacteria — both can be hard to identify

We have all heard of coronavirus being one of the main causes of viral scours in newborn calves. It alone, with a couple strains of rotavirus, are the two main viruses we see in scours vaccines. It also causes a winter dysentery (bloody diarrhea) in mature cattle, especially housed dairy cattle in the winter. What you may not have known is this same virus can be involved in the bovine respiratory disease complex.

The respiratory syndrome is often masked by the other much more prominent viruses such as IBR and BRSV or the main bacterial causes of pneumonia, that being Mannheimia hemolytica, Pasteurella multocida and finally Histophilus somnus. Often coronavirus may be involved with the respiratory disease complex with these other components, but is generally less serious. There is no respiratory vaccine on the market, which has the coronavirus antigen in it, but in the future as the vaccines have broader spectrum, possibly a company may put in the coronavirus to bolster the immunity to more respiratory pathogens once again.

Capacity low, demand high

We all know respiratory disease is the No. 1 economic disease in feedlots across Canada so anything we can do to reduce cases and curb antibiotic usage is beneficial. Cattle have a lot less lung capacity than other species and yet with the big rumen and digestive process require a lot more oxygen, so technically the lungs have very little reserve in them. Hence, we have more issues with respiratory disease in cattle generally.

A few separate outbreaks of coronavirus respiratory disease have occurred. You generally see some slight depression, but overall animals will still look bright. There may be increased nasal secretions and feed intake may go down significantly. In fact decreased feed intake may be the first symptom observed.

One still has to treat the sick calves for secondary bacterial infection. A suppression of the immune system for a number of reasons such as vitamin or mineral deficiency, internal parasites or concurrent disease are other reasons coronavirus may occur. You may even have some cattle infected with the enteric form of coronavirus as well. You would then expect to have diarrhea accompany some of the other clinical signs in a small percentage of infected cattle.

So if a group of cattle seem to be sicker than in the past in spite of vaccinating for pneumonia have them checked out, as the coronavirus may be the culprit.

New one to watch for

Another bacterial cause of pneumonia presents itself a different way and may be an emerging disease in the U.S. We should keep our eyes open in Canada with all the trading of cattle and other livestock that goes on. The bacterium is Bibersteinia trehalosi and is very closely related to M. hemolytica — the key bacteria involved in the whole bovine respiratory disease complex. It presents itself as sudden death. In the U.S. it has involved Holstein cows primarily and is significant at causing pneumonia and blood infection (septicemia) in sheep. The pneumonia veterinarians see on a post-mortem is really indistinguishable from the M. hemolytica form. It is difficult to identify since it also has a specific test in the lab, as well. It may be another emerging component to the whole respiratory disease complex.

U.S. veterinarians first noticed this form of pneumonia because it was a quick killer of cows and fairly unresponsive to antibiotics. That’s partly due to the acute nature of the disease, which simply doesn’t give the antibiotic enough time to work. Also we generally are not expecting full-grown cows to develop respiratory disease, so it catches us off guard. In some cases this organism can be quite resistant to many different antibiotics.

Even though there are several good long-lasting macrolide antibiotics for treating groups of high-risk calves, this should not alter our vigilance of watching for unusual respiratory disease and trying to prevent it. If the incidence of treatment or death loss is higher than expected or there have been sudden deaths, get some of these autopsied by your veterinarian. Finding the root cause will definitely help them determine better treatment, biosecurity and preventative measures for your farm.

Vaccines effective

Cow-calf, feeder and feedlot operators have definitely decreased the incidence of pneumonia deaths in Canada over the last decade. They’ve done this by combining vaccines with broader coverage, using metaphylactic antibiotics with better treatment antimicrobials, along with anti-inflammatory drugs that veterinarians prescribe. Feed conversion is improved with less-chronic presents.

If you’re seeing poor response to vaccines, more calf pulls or death rates are unacceptable get the cattle checked and post-mortems performed on suspect animals.

One of these emerging pathogens especially B. trehalosi could be present and you need to do a culture to find out. Be aware of new advances in the early detection prevention and treatment of respiratory disease. Different vaccination combinations are always presenting themselves and there is always going to be continued research in this area of cattle medicine.

About the author

Columnist

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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