About this time last year, I had an opportunity to visit New Zealand to attend a conference on animal health surveillance.
I enjoyed touring the beautiful countryside and seeing the large numbers of farms mostly populated with sheep and dairy cows.
Lately, a lot of news is coming from the veterinary community in New Zealand while it deals with a new bacterial infection in dairy cattle known as Mycoplasma bovis.
Biosecurity is being emphasized on these farms as they try to control the infection and prevent it from spreading.
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Unfortunately, this disease has been well established in North American cattle herds for years.
Mycoplasma bovis is a bacterial species commonly found in the upper respiratory tract of cattle. Mycoplasmas are very small bacteria that lack a cell wall and are relatively primitive and therefore have to rely on the host cells for much of their survival. However, despite seeming to be a relatively normal and harmless inhabitant of the nasal passages of many calves, it can occasionally become an agent that causes severe disease in cattle.
Here in Western Canada, we know that Mycoplasma bovis can be an important cause of pneumonia, arthritis, ear infections and mastitis in cattle.
We still don’t completely understand how this agent in nasal passages of normal healthy cattle can suddenly go rogue and cause such serious diseases. In feedlot calves, mycoplasma is well known for causing severe chronic pneumonia and arthritis, which is often very difficult to treat.
Most feedlot managers and pen riders are familiar with the swollen joints and non-responsive pneumonias associated with these bacteria. In addition, similar infections can occur in bison, where it can cause especially severe disease and high levels of mortality.
M. bovis is also an important cause of mastitis in dairy cows and is fairly widespread. A 2002 survey of dairy herds in the United States estimated that almost eight percent of 871 dairies tested were positive for mycoplasmas in their bulk tanks.
The first major outbreaks of mycoplasma-related diseases in young calves were identified in calf ranches in the U.S. where a large number of dairy calves are fed and raised.
These calves were fed waste milk and that milk had become infected with M. bovis. Because waste milk is typically batched for feeding to calves, a single cow that was infected with M. bovis mastitis could potentially contaminate a large batch of milk and infect many calves.
Once infected with the bacteria, calves could also pass it from calf to calf in respiratory secretions. Issues such as pen design, barn ventilation and stocking density could make this transmission even more effective and there was also some evidence that the environment around the pens of these calves could become contaminated and infect the next calves housed in the same area.
The typical signs of M. bovis infections in young calves are seen as pneumonia, arthritis or ear infections or any combination of these.
The respiratory disease syndrome would be similar to many other causes of pneumonia and the typical symptoms would include fever, coughing, nasal discharge and loss of appetite. Some calves may also have signs of arthritis that would manifest itself in painful, swollen joints, which can also cause severe lameness. Arthritis seems more common in feedlot calves, but it can also occur more sporadically in pre-weaned calves.
One of the more characteristic signs of mycoplasma infections in young calves is an ear infection. Calves would typically have an ear drooping, show signs of head shaking or scratching and may have pus coming from the ear canal.
Clinical signs of infection in young calves usually appear at two to six weeks of age. In dairy calves, we believe that the infection of the inner ear occurs because calves are fed waste milk that may be infected with M. bovis, which can contaminate the Eustachian tubes leading from the throat to the middle ear. The result is an ear infection or a pneumonia.
We see this disease in young beef calves as well, but less is known about the risk factors that might predispose a herd to have an outbreak associated with M. bovis. It could be that, like dairy cows, some beef cows are infected with mycoplasma in their udders and calves become infected when they suckle the dam’s infected milk. Once a few calves are infected, they may then spread the infection to other calves through their respiratory secretions.
If you suspect you have a calf with an infection caused by mycoplasma, you should take prompt steps to isolate it from the rest of the herd to prevent the infection from spreading to other young calves.
Antibiotic treatment of these infections is usually recommended but is often not very rewarding. Ear infections and pneumonia cases may respond if treated early in the course of disease, but joint infections are notoriously difficult to treat.
Unfortunately, we lack effective vaccines to control this particular disease in calves.
We know that good management practices that help to control other respiratory diseases will probably help control Mycoplasma bovis.
There are steps to help minimize this disease if it does occur on your ranch:
- make sure calves have good colostral intake
- use good vaccination protocols for infectious bovine rhinotracheitis virus, bovine viral diarrhea, bovine respiratory syncytial virus and parainfluenza-3 virus and other causes of respiratory diseases
- ensure calves are not crowded or exposed to a calving barn with poor ventilation
