Infectious causes of abortion in sheep
Listed below are the common infectious agents that cause abortion. It should be remembered that other diseases of sheep, such as pregnancy toxaemia and fluke infection can also result in abortion.
Some of these agents can cause serious human infection, and strict hygiene must be practiced when handling aborting ewes, and the products of abortion. In particular, pregnant women, and individuals who are immunocompromised should not participate in lambing if there is any risk of exposure to them. General precautions
are also listed at the end of this article.
Enzootic Abortion of Ewes (EAE)
This bacterial infection causes late abortion irrespective of when the ewe was infected, and may even be when it was not pregnant. Infection can also cause still-births, or the production of live weak lambs. The placenta is characteristically red and inflamed with a creamy-yellow discharge. If an outbreak occurs, administration of an oxytetracycline may help reduce losses. This infection can cause serious human illness including abortion in pregnant women.
This is a protozoan infection, where the main risk is from cat faeces contaminating sheep feed. Depending on the stage of pregnancy at which infection occurs, there may be: foetal resorption, which manifests as
barren ewes, abortion, production of mummified lambs, or birth of live weak lambs. Once infected, the ewe becomes solidly immune and should not abort again due to this infection.
Campylobacter species bacteria
Abortion or the birth of live weak lambs due to campylobacter infection normally occurs in the last six weeks of pregnancy. Ewes may or may not exhibit diarrhoea.
Salmonella species bacteria
Ewes may become very ill when aborting due to salmonellosis.
Q fever is caused by the bacterium Coxiella burnetii and is a sporadic cause of abortion in sheep and goats. It can cause severe flu-like symptoms in humans.
Listeria monocytogenes is an environmental bacterium found in the soil, and abortion is often associated with feeding silage contaminated with soil.
It is important to diagnose each cause of abortion, as control measures will be different for each of the agents listed above. Submission of aborted lambs and placentae to the Veterinary Laboratories Agency, in consultation with your vet, is the best means of diagnosis. Your vet may also advise blood sampling of aborting or barren ewes to test for EAE and Toxoplasma.
Having reached a diagnosis, your vet can advise on the best means of control. Vaccines are available to aid control of EAE and toxoplasmosis. General precautions are listed below.
- Remove and dispose of aborted lambs, placentae and contaminated bedding, and disinfect the area.
- Isolate aborting ewes, ideally for three weeks, or until discharges have stopped. Identify these ewes for
possible blood sampling later.
- Do not use ewes that have aborted for fostering lambs.
- Breed your own ewe replacements or source from flocks of known health status.
- Discourage breeding cats, as young cats are most likely to transfer toxoplasmosis.
- Bird droppings and the faeces of other animals can be a source of both Campylobacter and Salmonella. Clean out feed troughs regularly, and cover feed stores.