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Mette Bisgaard Petersen, Liza Rosenbaum Nielsen and Matt Denwood
"The cows died and we did not know why," farmer Tage Lausten told the Danish Farming News seven years ago.
Lausten felt helpless and did not know what to do when many of her cows contracted pneumonia. arthritis
What Lausten and the vet did not know at that time was that the cows had been infected with the bacterium Mycoplasma bovis. Since then, at least 120 herds have experienced similar epidemics with significant consequences for animal welfare and economic losses for affected Danish farmers.
Our research shows that a relatively inexpensive and easy laboratory test makes it possible to identify whether sick cows are probably infected with the bacterium Mycoplasma bovis. This is done by measuring the amount of antibodies in the blood and milk of a group of cows.
But the test must be performed at the right time in relation to the course of the disease, and a correct interpretation of the test results requires knowledge of the disease
How do the tests work? antibodies
When cows are infected with bacteria or viruses, the immune system starts to fight the infection. Some blood cells produce antibodies that help fight the infection.
These cells remember and recognize the infection and react quickly if the cow is re-infected. This is the same mechanism that is used in many vaccines.
For example, when a person is vaccinated against tetanus, the amount of antibodies against the tetanus bacteria subsequently increases in the blood. Antibody responses can therefore also be used to establish a diagnosis in humans – or cows – by measuring the amount of antibodies against specific bacteria.
These types of tests are often called antibody tests and are commonly used to diagnose diseases. animals and persons
Mycoplasma bovis destroys the immune system
The bacterium Mycoplasma bovis is rather special. It can influence the immune system so that it does not work as well.
Bacteria can also change surface to hide from the cells of the immune system, making it more difficult to recognize the bacteria the next time the animal is exposed to them. It's almost as if the bacteria were wearing invisibility cloaks.
This is probably the reason why the antibody test should be interpreted differently for Mycoplasma bovis than for other bovine diseases.
To understand how to interpret the test, we studied four dairy herds Mycoplasma bovis
We measured the amount of antibodies against Mycoplasma bovis in blood and milk samples from healthy and sick cows over a period of 12 weeks and compared the results.
The antibodies fluctuated a lot and only increased sick cows for a short period of a few months. Importantly, this contrasts with what is normally found for other diseases, where the antibodies may remain high for years after
Farmers and veterinarians must take this into account when they use the test and interpret the test results.
We found that the amount of antibody produced in response to different clinical signs varies a lot from one cow to the next. This adds an additional complication in the diagnosis of the disease.
The bacterium is easily missed
In addition, our results show that antibody tests in milk samples can only identify cows with Mycoplasma bovis. Mycoplasma bovis is not pneumonia or arthritis
Since the preferred method of analysis in dairy herds is often on milk samples, you can see how easy it is to miss . to the animal, so it is important to measure the antibodies in a group of animals and not just one or two cows as is often done. It is only then that you can see if the herd has a disease caused by Mycoplasma bovis
Faster treatments of infected flocks
In 2011, when Lausten Tage and d & # 39; other farmers were losing cows to Mycoplasma bovis, veterinarians I do not know how to interpret antibody tests, which made it difficult to diagnose and treat quickly.
These new findings will help farmers like Lausten and veterinarians to quickly identify Mycoplasma bovis infections and administer appropriate treatment and control measures. This will facilitate the early identification of the disease and limit the negative consequences for farmers and animals.
In the longer term, this could lead to the development of new certification programs where herds are continuously tested and the transmission of infection between herds. can be reduced.
Learn more:
New Zealand kills 150,000 cows to end bacterial disease
More information:
Mette B. Petersen et al. A longitudinal observational study of the dynamics of Mycoplasma bovis antibodies in naturally exposed and sick dairy cows, Journal of Dairy Science (2018). DOI: 10.3168 / jds.2017-14340
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