Tremendous effort and resources are put toward reproductive management on our dairy farms. It is disheartening to see all of this work go to waste when the cow subsequently aborts after being diagnosed pregnant. Knowing how to evaluate and minimize the risks of abortions in your cows is an important part of your reproductive program.
The normal gestation length for a cow is 282 days; however, there can be variability in the time the cow actually calves by up to 10 to 15 days. Hot weather and other forms of stress can cause cows to calve earlier than normal. Typically, we classify an abortion as a cow calving more than two weeks early with a stillborn or abnormally small calf. One of the important aspects of managing abortions is to have accurate calving data on all of your cows, such as breeding dates, and pregnancy confirmation dates to match those breeding dates. Accurate records are necessary for evaluating all parts of reproduction. For bull-bred herds, it is important to have your veterinarian regularly do reproductive exams, as the accuracy of pregnancy detection greatly decreases with increasing length of gestation. Ask your veterinarian when he or she would like to check the cows to improve the accuracy of predicting calving dates.
What is a normal abortion rate for a dairy farm? Some research shows that it is normal for cows to lose up to 15 percent of calves from pregnancy diagnosis to calving. The higher abortion rates are those fetuses less than 40 days gestation. Any abortion rate greater than 5 percent should be evaluated by your veterinarian.
There are multiple causes of abortion and many of them are infectious and contagious. IBR (Infectious Bovine Rhinotracheitis) and BVD are two important viral causes of abortion. The most common effects of BVD are not intestinal, but rather reproductive such as abortions and failure to conceive. Leptospirosis is a bacterial cause of abortion that has the potential of being transmitted to people. The bacteria reside in the kidneys and are spread via urine. Brucellosis is another bacterial cause of abortion that has been eliminated in several areas of the country, but is still present in some states and the wildlife population. It is also contagious to people.
One of the most common causes of abortion today is Neospora. This is a protozoal parasite that has the dog as the intermediate host. The dog can shed cysts in the feces which if consumed by the cow can lead to infection. No signs are typically seen in the cow except for abortions, often late in gestation. Cows can become carriers of this organism and abort multiple times or infect their fetuses who then become carriers.