Abortion is one of the major causes of economic loss in the dairy cattle industry. Hovingh, an Extension Veterinarian in Virginia, estimates a cost of $500 to $900 per occurrence (2009). This includes costs associated with loss of milk production, feed and replacement costs. At such an expense, it is no wonder dairymen may become concerned about pregnancy lost and want to better understand possible causes and prevention methods.
The word abortion is usually used to define the termination of a pregnancy; however a distinction should be made between early embryonic death, abortions and stillbirths. Early embryonic death is pregnancy loss before the organogenesis (the formation of the calf’s internal organs) is complete, which usually occurs around day 42 of gestation. Pregnancy loss between days 42 and 260 of gestation is considered a true abortion. Stillbirth occurs anytime a calf dies from 260 days of gestation up until 24 hours post calving. Knowing the difference between these observations helps ensure the problem is investigated correctly.
To determine if abortions are an issue on a dairy a good place to start is to compute a monthly abortion rate (divide the number of abortions by the number of pregnancies generated that month). Data from a USDA dairy report indicates 72.5% of all interviewed operations had a 4.9% or less annual abortion rate and 27.5% reported annual abortion rates range at 5.0% and above (2010). I would consider abortions a problem if a farm has an annual abortion rate greater than 6%; however, every farm has a little different management scheme so one could set a goal on an individual herd basis.
There are multiple causes of abortions in dairy cattle. Perhaps the most frequent cause is infectious agents such as bacteria (Brucelosis, Leptospirosis, Salmonellosis, Haemophilus sommus, Mycoplasma, Listeria). Other causes include viral agents (Bovine Viral Diarrhea and Infectious Bovine Rhinotracheitis); other agents (Neospora caninum, Trichomonas and Campylobacter fetus); fungi and mycotoxins; genetic abnormalities; heat stress; and even infection conditions that do not directly affect the fetus. Research by Risco, Donovan and Hernandez at the University of Florida indicates, “Cows that had clinical mastitis during the first 45 days of gestation were at 2.7 times higher risk of abortion within the next 90 days than were cows without mastitis” (1999).
It may be difficult to determine the cause of abortions due to lack of evidence and/or deficient samples from which to determine the cause. To better determine a reason work with a veterinarian to select and prepare the proper samples to submit to a laboratory. Good sample sources include the whole fetus, the placenta or a blood sample from the dam.
Prevention must be centered on keeping accurate records and collecting good samples for laboratory analysis. As indicated in Table 1, employing good biosecurity practices that inhibit the introduction and spread of infectious agents and utilizing vaccination programs could limit abortion occurrence. Maintain the general health and immune function of animals by providing a well-formulated ration, clean water and a clean/dry environment.
Hovingh, E. 2009. Abortion in dairy cattle -1: Common causes of abortion. Virginia Cooperative Extension. Web.
Risco, C.A, G.A. Donovan, and J. Hernandez. 1999. Clinical mastitis associated with abortion in Dairy cattle. J. Dairy Sci. 82(8): 1684-1689.
USDA. 2010. Biosecurity Practices on U.S. Dairy Operations, 1991–2007.