Q.
What can cause a ewe/doe to abort her offspring?
A.
Abortion is when pregnancy is terminated and the ewe/doe loses her offspring or gives birth to weak or deformed lambs/kids that die shortly after birth. Sometimes, the ewe/doe gets sick, too (even dies; especially with salmonella). Young females are usually the most vulnerable. There are many causes of abortion, both infectious and non-infectious. The three most common infectious causes of abortion in ewes/does are campylobacter (vibrio), chlamydia (enzootic abortion), and toxoplasmosis.
Vibrio
Abortions due to campylobacter organisms (vibriosis) usually happen in late pregnancy or result in still births. If infection occurs in early gestation, the ewe/doe will reabsorb the fetus. The route of infection is oral. Strict hygiene is necessary to prevent an outbreak. Vibrio abortion can be controlled by vaccination. The vaccine should be given 30 days prior to breeding and again in mid-gestation. After that, boosters can be given during mid-gestation. Long acting antibiotics or daily injections of antibiotics may help. Antibiotics may have limited efficacy due to resistance issues. Aborting females are usually immune to the effects of the disease.
Chlamydia
Chlamydia causes enzootic abortions in sheep/goats. Late term abortions, still births, and weak lambs/kids are common. Abortion occurs mostly in the last 2-3 weeks of pregnancy regardless of when the ewe/doe was exposed. Ewes seldom abort more than once, but they remain persistently infected and shed the organism for 2-3 days before and after ovulation. Rams can also be infected and transmit the organism. The products of abortion are by far the greatest source of contamination and transmission. Ezootic abortions can be controlled by feeding antibiotics and vaccination. Antibiotic injections can also be given in the case of an abortion storm.
Toxplasmosis
Abortions caused by Toxoplasma gondii can occur at any stage of pregnancy. Early exposure usually results in reabsorption or mummification. Later exposure causes abortion and prenatal death. In an outbreak, there is usually a wide range in the gestational age of aborted fetuses. Once infected, ewes/does are immune to reinfection. There is no vaccine for toxoplasmosis in the US (there is one available in other countries). However, feeding a coccidiostat late in pregnancy may help to reduce abortions.
Toxoplasmosis is a protozoan parasite. It can only complete its life cycle in a member of the cat family; thus, cats are the carriers. Sheep/goats get infected when they ingest oocysts excreted in cat feces. The oocysts are found in contaminated feed, water, bedding, and pasture and remain infectious for long periods of time. The best protection is to safeguard feed supplies from cat feces and empty feed troughs regularly. Young cats are the main shedder of the parasite. A stable population of neutered farm cats poses little risk. If ewes/does are exposed prior to pregnancy, they will develop immunity.
Less common causes of infectious abortion include listeriosis. leptospirosis, salmonellosis, brucellosis, bluetongue, border disease (BVD), Q fever, and cache valley virus. Cache valley virus is mosquito-transmitted. it's noteworthy because it causes congenital abnormalities (deformities) in the fetuses. Q fever (Coxiella burnetii) is becoming increasingly important because it is highly contagious to people. Q fever abortions are more common in goats than sheep.
Biosecurity is the best protection against all infectious causes of abortion. Maintaining a closed flock will minimize the introduction of new diseases to the farm. Biocontainment will help to minimize outbreaks. Females that give birth to dead/weak full-term offspring should be isolated. Aborted material and bedding should be removed and destroyed. Fetuses and placenta can be submitted to a diagnostic lab to determine cause. Serology can diagnose a couple of the abortion organisms: toxoplasmosis and cache valley
Most of the infectious organisms that cause abortion in sheep/goats are zoonotic and can be transmitted to people. Flu like symptoms are most common, but some of the organisms can also cause miscarriage. People get infected by direct contact with animals and their environment or by ingesting contaminated food and water. Pregnant women and immuno-compromised individuals should not handle fetuses, afterbirth, or birthing fluids. Gloves or sleeves should always be worn when handling these materials or assisting with births. Good personal hygiene (hand washing) is important. Food should be properly cooked. Milk should be pasteurized.
Other causes
There is anecdotal evidence that dewormers can cause abortion in sheep/goats. The claim is unsubstantiated with the macrocyclic lactones (ivermectin, moxidectin). The claim that levamisole causes late term abortion (in goats) is taken more seriously. Even though there is no scientific proof, it's probably a good idea not to administer levamisole to goats in late gestation. Albendazole (Valbazen®) can cause abortion in early pregnancy. The label says to not give to ewes in the first 45 days of pregnancy or 45 days after the ram is removed. There is no pregnancy risk with the other benzimidazoles (e.g., fenbendazole, Safe-Guard®) or with copper oxide wire particles.
Certain nutritional deficiencies (energy or micronutrients) may cause abortion. Stress can cause abortion. Some drugs will halt pregnancy. Dexamethasone is a steriod used to treat various disease conditions. It is also given to induce labor. It should not be given to pregnant females unless labor is the goal. Lutalyse® (prostaglandin) will also cause abortion or induce labor in goats. Sometimes, it is used to terminate an early pregnancy or induce a late one.
It is always important to read labels to make sure a drug is safe for a pregnant female. If you're not sure, be sure to consult with your veterinarian.
5/5/21
Additional reading
Infectious causes of abortion in sheep - Cornell University
Control of toxoplasma abortion in sheep - Moredun Institute
Toxoplasmosis: common cause of abortion in sheep and goats
Toxoplasmosis: what does it mean to your, your family, and your animals?