I was asked to talk about Toxoplasmosis and additional information is available in our Veterinary Guide book or on the blog site but for today I am going to review how the organism infects sheep and goats. Cats become infected by animals infected with the parasite usually rodents or small birds. Rodents pass the organism from generation to generation through congenital infection, therefore rodents act as long term reservoir of infection. After ingestion, oocysts begin to pass in three to five days. Shedding is short in duration, usually 7 to 20 days. Enormous numbers can be passed. Two hundred million oocyst may be excreted, with 50 grams of cat feces containing up to 10 million oocysts.
The oocyst can survive in the environment for at least a year, easily tolerates cold climate, arid climate not as well. Sheep and goats are infected by eating oocysts from pasture, hay, grain or contaminated water. As few as 40 oocysts are required to infect a ewe or doe. Cats occupy hay sheds and feed storage areas and by defecating on feed it becomes infected. Feral cats have large territories and roam extensively defecating on pasture. Direct sheep to sheep spread at lambing has not been proven but consumption of infected placenta will infect cats.
What does this all mean? Young cats are the most likely to become infected and spread oocysts so it makes sense to keep a stable, adult, neutered, cat population. Certainly, no cats at all is not the answer. If I could use the vaccine used in New Zealand I would do it in a heartbeat. Just maintaining a normal farm cat population is not all bad. Feeding hay and feed that is suspect of contamination to non-pregnant animals is a good idea. The use of Deccox or Rumensin during pregnancy is a recommended practice and has an added benefit of reducing exposure of coccidiosis to the lambs.
Let’s do the math, according to my calculations one gram of infected cat feces mixed with feed can infect 5,000 ewes or does. Exposure to nonpregnant females is the best answer but confirmation is difficult so the use of Deccox or Rumensin is prudent. Rumensin is commonly fed at 15 to 30 mg per head, 15mg is adequate. 2# of 6% Deccox in fifty pounds of loose salt is the most practical way to provide Deccox.
