Blood on the Snow: Dealing with Abortion Storms in Cattle and Sheep
This is the time of year when veterinary diagnostic laboratories around the country see peak submissions of aborted and stillborn calves and lambs. You and your vet often have a hunch about what caused the problem. The only way to confirm it is at a veterinary diagnostic laboratory, which in our state is the Wyoming State Veterinary Laboratory in UW’s College of Agriculture.
It often takes three of us – you, your vet, and the diagnostician – to figure out what is going on.
An abortion rate of less than two percent should not cause alarm. These ‘spontaneous’ abortions are due to genetic abnormalities, hormonal imbalances, placental/uterine disease, and opportunistic infections. Such losses may occur at the start of calving and abruptly stop. But owners should be concerned when they recognize a repeat breeding problem, a string of abortions, or when abortion rates creep above three percent.
Causes of Abortion
Important causes of livestock abortion in Wyoming are infectious and, to a lesser extent, toxic.
In cattle, these are bovine viral diarrhea (BVD) virus, miscellaneous bacterial infections, infectious bovine rhinotracheitis (IBR or “red-nose”), nitrate poisoning, ponderosa pine needle abortion, twins, lupine intoxication, and Tritichomonas foetus (“Trich”). Trich causes early embryonic death, resulting in open cows/repeat breeders rather than abortions. An uncommon but spectacular cause of abortion is inappropriate use in pregnant cattle of modified live vaccines for BVD and IBR. Uncommon causes of abortion are physical injury, any infectious disease that makes cattle systemically ill (e.g., shipping fever), and moldy hay. Starvation rarely causes abortion but contributes to stillbirth and weak calves.
Brucellosis is once more eliminated in Wyoming cattle, based on federal slaughterhouse surveillance. But it persists in free-ranging elk and bison in the western part of the state. Brucellosis causes explosive outbreaks of late term abortion in cattle. Because it is so highly infectious, these outbreaks need to be identified and contained immediately.
In sheep, common infectious causes of abortion in Wyoming and the region are campylobacteriosis (“vibrio”), miscellaneous bacterial infections, Q fever (short for query fever), Chlamydophila abortus, and salmonellosis. Rabbit fever due to Francisella tularensis causes abortion in heavy tick years and when rabbits are numerous – we saw outbreaks of this disease in 1997 and again in 2007, fortunately without any human disease.
That’s two relatively long lists of abortions agents in cattle and sheep. Unusual agents can be introduced when pregnant cattle or sheep are purchased from out of state. Neosporosis is a common cause of abortion in dairy states. We have yet to confirm it in Wyoming cattle. Toxoplasmosis in sheep is common in some parts of the United States. Again, it is rare here, but it could be introduced at any time.
If You Think You Have an Abortion Storm
If you believe there is an abortion storm in your herd or flock, apply some basic principles. First, protect the rest of the herd or flock. If you suspect the cause is infectious (more than three to five percent abortions; multiple losses in a short period; highest losses among naïve or young stock; illness in dams), isolate affected cattle or sheep from the rest of the herd. Use common sense when handling and feeding animals that aborted. Disinfect abortion tissues and fluids, and then burn or bury them. Wear gloves when doing so. You do not want to transfer infection to the healthy part of the herd on your hands or contaminated clothes. Once you get a diagnosis, and, with the advice of your veterinarian, consider vaccinating or treating in the face of an outbreak. In sheep, depending on the agent, you can reduce losses by mass treating the flock with an appropriate antibiotic.
Second, get a diagnosis. Submit samples through your veterinarian to a diagnostic laboratory. The best samples are a chilled (not frozen) fetus with a sample of placenta, and a tube of blood from the animal’s mother. BVD virus is now a big concern, and there is a belief that submitting skin from the ear of an abortus will allow the laboratory to rule out BVD. Unfortunately, we need an entire carcass to check for this agent. Submit feed and water, if you are worried about them, although it is rare for either to cause abortion in our area. Let us decide what is rotten and what is worth working up.
Diagnostic laboratories get a diagnosis in only 30 percent of cases when presented with a single fetus from an outbreak. The diagnosis rate jumps to 60-80 percent when multiple fetuses and placentas are submitted. A common reason for the laboratory report that states “No abortion agent identified” is that the fetus was dead for days, weeks or even months before it was expelled. Infectious agents are destroyed by the decay process after death, so that it takes the submission of multiple fetuses with their placenta to pinpoint the cause. Even if the coyote got to the fetus before you did, you still have the cow. For some diseases, particularly brucellosis, a diagnosis is readily made using blood from the dam. If your circumstances are a real wreck and losses continue, you will see more fetuses. Submit those.
Third, protect yourself. One cause of abortion in cattle – brucellosis – and many causes of abortion in sheep are transmissible to people. These can be nasty and, in rare instances, fatal. Family members who are pregnant or have an immunosuppressive disease should avoid cattle and sheep that have aborted and any products of abortion.
Fourth and not least, think about your neighbors. If abortion occurs in your herd, and you suspect it is infectious, do them a favor – let them know. Some abortion diseases are reportable (brucellosis and trichomoniasis in cattle; toxoplasmosis, Q fever and tularemia in sheep). That means the Wyoming Livestock Board (WLSB), in the form of the state veterinarian, needs to be informed of the episode. What happens next depends on the disease. If it’s trich, the WLSB will follow a specific course of action, primarily aimed at identifying where infection originated. In other instances, the state veterinarian just needs to know despite no requirement to take action.
It will take a full-service laboratory such as the WSVL three to four weeks to complete an abortion workup. That seems like a long time when you are in the middle of an abortion storm. If you are experiencing a big problem, don’t assume the submission of one fetus will generate the answer. Let your veterinarian know that losses continue. Talk to personnel at the WSLV so we can focus on specific possibilities, expedite testing, and obtain additional samples. In some cases, you may get the laboratory answer after the abortion storm has passed. The information is still valuable. It tells you something about your herd you can use to improve biosecurity. It may help avoid heartbreak in subsequent years.
The WSVL website is http://wyovet.uwyo.edu/Default.asp. Quick Links at the site also include how to take various samples. The telephone number for the lab is 307-722-6638. Current information on specific diseases is available at the Department of Veterinary Sciences’ website.
Donal O’Toole is a professor in the Department of Veterinary Sciences in the College of Agriculture at the University of Wyoming and a staff member of the Wyoming State Veterinary Laboratory. He can be reached at the laboratory’s telephone number or at email@example.com.