Toxoplasmosis, a disease caused by sheep ingesting oocysts shed by cats on pasture or in contaminated feed, bedding or water, is one of the most common causes of infectious abortion.

Teagasc advisor, Edward Egan had the following to say with regards to it: If abortion levels in your flock are greater than 2% then you need to find out why.

Toxoplasmosis [Toxo] is one of the most common causes of infectious abortion. Problems due to Toxo involve embryo/foetal loss, barrenness, late lambers, late abortions, weak lambs and helping a ewe to lamb rotten lambs. 

How are ewes infected?

Toxo is not spread from sheep-to-sheep. Young cats spread it to sheep. The young cat first becomes infected from eating an infected mouse or bird (mice or birds do not spread Toxo to sheep). 

The infected young cat then spreads the disease to sheep by dunging in meal, fodder, straw, water or pasture. The infected cat remains infectious for a week or so after which it develops life long immunity and no longer spreads Toxo while it is healthy.

How does Toxo affect your ewes?

The time the ewe is infected decides how she is affected and what the farmer sees. The infection of a non-pregnant ewe results in immunity within four weeks of the first infection. 

Infection in early pregnancy results in embryo loss without visible signs. These ewes will return to the ram and lamb late or appear barren if the ram has been removed. 

The most common time of infection is mid-pregnancy as ewes are coming in contact with infection in meal, straw, housing or fodder. If ewes are infected in mid-pregnancy they abort 45 days later – in late-pregnancy.

Infection in mid-to-late pregnancy results in affected ewes lambing a few days early.

A large percentage of lambs although outwardly normal, will be stillborn and sometimes accompanied by a ‘small mummified chocolate brown lamb’.

Twin lambs may be very uneven in size, one being smaller and less developed than the other. In addition, a proportion of the lambs born alive will be weak and die within the first few days of life, despite your best efforts. Such lambs have brain damage.

Another common form of late abortion is a high incidence of one live lamb born with a dead lamb. Mummification and leathery or white-spotted placenta is an important indication of Toxo abortion.

Procedure for dealing with aborted ewes

Seven key steps to dealing with any aborted ewes:

  1. Abortions should “always” be considered infectious until otherwise proven so act fast;
  2. Isolate and permanently mark the ewe as blood samples may be taken later;
  3. Remove aborted lambs and cleanings. Adequately disinfect after inspecting aborted ewes or dealing with infected material;
  4. Contact your vet for advice;
  5. Collect samples of the foetus / lamb and cleanings and arrange testing through your vet;
  6. Carefully dispose of bedding and all other infected materials;
  7. Once the cause has been identified, consult your vet for the best control methods.