We have a small herd of about 60 cows. During a one-month period, four cows aborted. They were at least six months along. We have a closed herd, so the only thing we vaccinate for is blackleg. What could be causing this, and what should we do to prevent future problems?
Diagnosing the cause of abortion in cows is always tough. Abortions can be caused by bacteria, viruses, protozoans, toxins in feed or pastures, genetic defects, heat and stress. To further complicate things, the event leading to an abortion can occur weeks to months before the abortion occurs, which really makes a diagnosis challenging.
If you notice a problem like this, and you still have cows in the herd that have not calved, have your veterinarian pregnancy-check the rest of the herd and bleed each one to check antibody titers that might indicate common abortive diseases. Ear notching and checking for BVD-PI (bovine viral diarrhea -- persistent infection) would also be a good idea. Bulls probably should also be tested for STDs (sexually transmitted diseases), especially trichomoniasis.
Serology, the titers testing, can be very difficult to interpret under the best conditions. Ideally, cows that aborted would have had paired samples tested immediately after abortion and then two to three weeks later to see if titers changed. Significant increase, or decreases, in titers levels may point to a specific disease. The fetus and/or placenta, if available, should always be preserved and submitted to a diagnostic lab for testing. The bad news is that even when you have the fetus and do the paired samples, the cause of less than 50% of abortions may actually be diagnosed.
While I always want to know the "why" of things, my focus is on preventing a future problem. The herd should be vaccinated as soon as possible. There is really no such thing as a closed herd anymore, and cattle are worth far too much not to have them vaccinated. Your veterinarian is your best resource for developing a vaccination and biosecurity program to help you prevent losses in the future.
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