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Veterinarian View | January 2023

A Culprit in BRD Cases

contributed article by Dr. Vince Collison, Collison Embryo and Veterinary Services,

Rockwell City, Iowa

Haemophilus somnus (H. somnus) is one of the key pathogens found in the Bovine Respiratory Disease (BRD) today. I recently saw an article showing pathogen incidence rates in submissions to the ISU Veterinary Diagnostic Lab and it showed H. somnus as the pathogen with the highest incidence rate. Our work in the field examining BRD cases has shown similar results to what was presented in this article.

H. Somus in BRD

H. somnus presents in other forms but has evolved into one of the major components of the BRD complex. Typically, on a postmortem we will see consolidation of the lower lung lobes without pleuritis. Currently, this is the presentation we see most commonly on examination of BRD cases. If we do see pleuritis it is usually milder with H. somnus than what we would see with M. hemolytica. In many cases, with H. somnus there is usually other pathogens present.

Three of the most common pathogens seen in conjunction are Pasteurella multocida, Mycoplasma bovis, and Bovine Respiratory Coronavirus. One of the other viral pathogens we see with H. somnus is Bovine Respiratory Syncytial Virus (BRSV). While we typically have seen H. somnus in combination with these other pathogens, it can be the sole pathogen in BRD as well.

Listed are the various forms of disease associated with H. somnus:

1. BRD complex. This is by far the most common form we will see in the field at this time. As previously described it is also commonly associated with other pathogens. We will see this in all ages of cattle from young 1 to 3-month-old calves with BRD to older weaned calves that are just getting started on feed. It also will be in the more acute cases you see in the first 7 to 14 days in the feed yard, as well as cases seen later at 28 days on feed. The cases seen later at 28 days will often have Mycoplasma seen in conjunction with H. somnus.

2. Otitis externa. This is an external ear infection commonly seen with drainage and a down ear. Other causes can be Mycoplasma and M. hemolytica, but H. somnus is always high on our list of causes.

3. Thrombotic meningoencephalitis (TME) or (brainer disease). This is caused when H. somnus causes vasculitis in the brain resulting in thrombosis in the brain. Symptoms are usually fever associated with neurological symptoms. Often these calves will stand with their head and neck stretched out in front of them from the pain associated with the brain thrombosis. Usually, these types of calves have a more guarded prognosis due to the brain damage. The other similar disease we see presented as brainers is polio.

4. Arthritis. H. somnus can get into the joints and will often be seen in feed yards that have been battling BRD complex. As BRD lingers on, H. somnus will also be systemic and will end up infecting joints in the legs. Mycoplasma will do this as well.

5. Myocarditis (infection of the heart muscle). This is commonly seen when there is a high morbidity rate associated with H. somnus. It will cause a higher death rate and some sudden death. We have seen severe cases of this when calves are not vaccinated for H. somnus and the disease spreads more easily.

6. Reproductive losses.

H. somnus can be a cause for abortion in cows. We will vaccinate some cow herds annually for this to help with prevention.

Controlling BRD

Vaccination is the primary means of prevention for H. somnus. It is a required component of the Iowa Green Tag program and the Gold Tag as well. The Gold Tag requires two vaccinations a minimum of 14 days apart. While vaccination is helpful, we can still see H. somnus in vaccinated calves, but probably at a lower incidence rate. Calves that are vaccinated will usually respond better to treatment than non-vaccinated calves provided they are caught early enough. In high-risk calves, metaphylactic treatment can also be an important method for control of H. somnus and BRD. Other factors related to proper nutrition and calf comfort contribute to reducing stress and spread of BRD. Calves that are acidotic will be more prone to BRD. Be careful to work rations up appropriately and watch bunk management. Control of coccidia as calves are started is also important in controlling BRD.

BRD Treatment

There are many antibiotics available today that are very effective for the treatment of BRD complex. These also are effective for H. somnus as well as the other bacterial components of BRD. The key to treatment with H. somnus is early treatment. H. somnus causes vasculitis (inflammation of the blood vessels) and is part of the reason it presents in so many forms of disease. The longer the calf goes without treatment, the more damage that is being done to the various systems resulting in more difficult recovery. If a calf looks off, do not be afraid to go ahead and pull it for treatment. Treatments will be much more rewarding the earlier you intervene. If in doubt, check the calf’s temperature. H. somnus will cause fevers like other pathogens in the BRD complex.

As always, getting your herd veterinarian involved with an effective prevention and treatment plan for your situation is important due to the complexity of H. somus.

Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC

in Rockwell City, Iowa.

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