Toxoplasmosis in Sheep: Abortion, Weak Lambs, and Cat Exposure

Toxoplasmosis is an infection caused by the protozoan parasite Toxoplasma gondii. In sheep, it is best known for causing reproductive loss rather than obvious illness in the ewe. Many adult sheep appear normal, but if a ewe is infected during pregnancy, the parasite can damage the placenta and fetus. That can lead to early embryonic loss, abortion, stillbirth, mummified fetuses, or live lambs that are weak at birth.

Cats and other felids are the parasite's definitive hosts. They shed infective oocysts in feces for a limited period after becoming infected. Sheep then pick up the organism from contaminated feed, hay, grain, bedding, water, or pasture. This is why cat access to feed rooms, lambing jugs, and stored forage matters so much.

The timing of infection during gestation affects what happens next. Earlier infection may cause resorption or abortion that is easy to miss, while later infection may result in stillborn or weak lambs. Because several diseases can cause abortion storms in sheep, your vet will usually want lab testing before labeling toxoplasmosis as the cause.

Toxoplasmosis in sheep is caused by infection with Toxoplasma gondii. Sheep are infected when they swallow sporulated oocysts from the environment. The most common source is contamination from cat feces, especially when young hunting cats or newly infected barn cats have access to feed storage, grain bins, hay, bedding, mineral feeders, or water sources.

Cats usually become infected by eating rodents, birds, raw meat scraps, or placental tissues. After that first infection, they may shed oocysts in feces for a short period. Those oocysts can survive in the environment and contaminate areas where sheep eat or rest. A ewe infected for the first time during pregnancy is at the greatest risk for abortion or weak lambs.

Risk tends to rise when feed is stored where cats can climb, sleep, or defecate. Open grain, loose mineral, uncovered hay, and indoor lambing areas can all become exposure points. Flock outbreaks may look sudden, but the underlying problem is often environmental contamination that has been building over time.

Your vet usually diagnoses toxoplasmosis by combining flock history, pregnancy losses, and laboratory testing. Because ewes may look normal, diagnosis depends heavily on the right samples. The most useful submissions often include the placenta, especially cotyledons, plus fetal tissues such as brain, lung, liver, and body fluids when available.

Veterinary diagnostic labs may use PCR, histopathology, fluorescent antibody testing, and serology. Placental tissue can be especially helpful because Toxoplasma often targets the placenta. Your vet may also recommend blood testing from affected and unaffected ewes to help interpret whether the flock has been exposed.

This step matters because toxoplasmosis is only one cause of abortion in sheep. Chlamydial abortion, campylobacteriosis, listeriosis, Q fever, border disease, and other infectious problems can look similar in the field. A confirmed diagnosis helps your vet build a prevention plan that fits your flock instead of guessing.

Prevention focuses on keeping cat feces away from anything sheep eat, drink, or lie on. Store grain, minerals, and milk replacer in sealed containers. Cover hay and bedding when possible. Keep cats out of feed rooms, bunks, mineral feeders, and lambing jugs. Promptly remove placentas, aborted fetuses, and dead lambs so cats cannot scavenge them.

Work with your vet on practical cat management rather than trying to solve the problem overnight. Young hunting cats are often the highest-risk shedders. Good rodent control, secure feed storage, and limiting cat access to high-value areas usually matter more than having no cats at all. In flocks with a history of toxoplasmosis, your vet may discuss preventive medication strategies during pregnancy, but these decisions should be tailored to the flock and local regulations.

Human safety matters too. Toxoplasma gondii is zoonotic. Pregnant people and anyone with a weakened immune system should avoid handling cat feces, aborted materials, placentas, and contaminated bedding. Gloves, handwashing, and careful cleanup are important. In the United States, there is no commercially available sheep toxoplasmosis vaccine in routine use, so management and biosecurity remain the main prevention tools.