– William P. Shulaw DVM MS, Extension Veterinarian, Beef/Sheep, The Ohio State University
Abortion in cattle occurs during all seasons, but because of the time of year most beef cows are bred, it is most frequent during the late winter and spring months. Actually, embryonic and fetal losses occur throughout the gestation period, but the term abortion usually is used only when the fetus is large enough to be found.
Causes: Abortion can be caused by many factors including genetic conditions that result in a defective fetus that can’t survive beyond a particular stage in gestation and toxins such as those found in Ponderosa pine needles and certain other plants. Most abortions in cattle are probably caused by infectious agents – viruses, bacteria, protozoa, and fungi. Determining the cause almost always requires laboratory assistance, and frequently, no cause can be found for isolated abortions. Normal losses should be less than 1- 2%, and an investigation to try to determine the cause should be done whenever losses exceed this level.
The most common infectious causes of abortion include 1) viruses – infectious bovine rhinotracheitis (IBR) and bovine virus diarrhea (BVD); 2) bacteria – leptospirosis caused by 5 serotypes of Leptospira, brucellosis (Brucella abortus has nearly been eradicated in the US, but it should always be considered as a possible cause for the foreseeable future), and listeriosis; and 3) protozoa – neosporosis, a relatively new disease caused by Neospora caninum. Unfortunately, none of these infections regularly cause symptoms in the cow or obvious changes in the aborted calf that allow us to determine the cause just by looking. Usually the fetus has been dead several days, or longer, before it is delivered. Sometimes it is in an advanced state of decay when it is delivered. Regrettably, more than one of these possible causes of abortion may be present in a herd at one time. They are all maintained in the herd by carrier animals. These factors make diagnosis difficult.
Diagnosis: Diagnosis of abortion requires putting together information concerning the herd history, such as animal movement in and out of the herd, past disease, presence of other animal species, timing of the abortions, and vaccines used, along with post mortem and laboratory findings. Sometime blood samples can be helpful, but often vaccine use or previous exposure to disease agents may confuse the picture. For these reasons, your veterinarian may want to collect blood samples from several members of the herd in addition to the aborting animals, and he/she will usually want to collect the samples as near the time of the abortions as possible and again, 4-5 weeks later. This gives a better picture of herd exposure.
The diagnostic laboratory can be invaluable in determining the cause of abortions. The entire fetus and placenta (afterbirth), if available, should usually be submitted. For samples to be helpful they must reach the lab as soon as possible after the abortion occurs. Producers can help make sure samples reach the lab in good condition by placing the fetus and placenta in separate clean plastic bags. The tissues should be kept cold, but freezing is usually not a good idea. Wrapping the bags up in an old rug or blanket along with bags of ice or placing them in a cooler with some ice packs will help keep them from deteriorating further until they can be taken to the laboratory or your veterinarian. The Animal Disease Diagnostic Laboratory of the Ohio Department of Agriculture has made abortion diagnosis a priority and has submission kits and instructions available for your veterinarian.
Prevention: Because most infectious diseases involve a healthy appearing animal serving as a carrier, producers should use caution in bringing new animals into the herd. Likewise, contact with other cattle at exhibitions can expose the herd to infectious agents that cause abortion. For some agents like BVD and leptospirosis, carrier animals may already be in the herd providing continual exposure and occasionally causing disease in non-immune animals.
Vaccines are useful tools to help prevent abortions. However, they are not guarantees. For example, cattle can abort because of infection with any of five strains of the Leptospira organism. They may shed these organisms in their urine for up to a year after infection. The vaccines currently available provide reasonable protection against abortion for 4 of the 5 strains, but they do not always prevent infection and temporary shedding. They do not stimulate strong immunity to Leptospira hardjo as this serotype has become adapted to cattle as the preferred host. Vaccine will not eliminate the carrier state and will not always prevent abortion and infertility caused by L. hardjo. In herds with confirmed leptospirosis problems, some veterinarians recommend vaccination 2-4 times in a year and strategic use of certain long acting antibiotics.
The virus of bovine virus diarrhea (BVD) exists as a family of different strains of the virus, and new strains are constantly appearing as a result of mutations of the virus. Herds have been identified with more than one strain circulating among non-immune animals. The available vaccines can protect cattle against infection with many, if not most, of the existing strains. However, protection against all strains is probably not possible. In addition, most vaccines for BVD are not labeled for protection against abortions. Fortunately, technology now exists to detect the carrier state, and it is possible to eradicate this virus from herds with testing. Testing and isolation can prevent introduction to the herd. This is especially useful in purebred herds and the small herds seen in Ohio. Suppression of the immune system and infertility are other important features of BVD infections.
Vaccines should be used in an overall herd health program as one measure of biosecurity. They can help prevent abortion but should not be relied upon as the sole prevention measure. Producers should work with their veterinarian to develop an overall program that reduces their risk of abortions and other disease.
Human health: The bacterial causes of abortion listed above, as well as several others, are all potential causes of serious human illness. Producers should always be cautious in handing aborted fetuses, afterbirth, and discharges from aborting cows. You may not know that the cow in labor that you are assisting is in the process of abortion until you have already been exposed. Wear plastic sleeves and wash the cow and yourself thoroughly after assisting her. Isolate the cow until you can be reasonably sure she is no longer shedding infectious material. Consider all abortion products and discharges potentially infectious. Wear clean clothes, and don’t wear potentially contaminated clothes and boots into the house where you may expose the rest of the family. Wash up frequently and don’t eat or rub your eyes without washing. Advise any employees of precautionary practices to prevent their exposure.
Not all abortions are preventable, but a sound herd health plan, a plan of biosecurity, and routine diagnostic procedures can limit their economic effect.