Enzootic abortion of ewes (EAE) is devastating to any flock, and though it is a disease that can be prevented and well managed, the All-Island Animal Disease Surveillance Report shows that levels of EAE nearly doubled between 2020 and 2021.

The bacteria chlamydia, that causes EAE, is transmitted in foetal material at lambing time or during an abortion. Yet, regardless of when a ewe becomes infected, EAE doesn’t actively cause disease until she is 80 to 90 days pregnant. If a ewe becomes infected when she is not pregnant, or later on in pregnancy, the disease is latent until that stage of her next pregnancy.

A high barren rate at scanning is often the first indication of a problem. Abortions are then seen in the last two to three weeks of pregnancy, along with mummified foetuses, stillbirths and the birth of lambs that are weak and struggle to suck.

A 2022 abortion survey showed that 44% of farmers didn’t investigate the cause of abortions on their farm. Our advice is to “test and don’t guess” as it is important to get a diagnosis – an aborted foetus and placenta is the best sample, but blood sampling or a vaginal swab can also be used.

In the face of an abortion storm, antibiotics are used to try and reduce abortion levels, however, they don’t reduce shedding of the disease, nor the incidence of ewes affected. It is, therefore, preferable to use the now-available inactivated vaccine to protect the rest of the flock, which reduces clinical signs and shedding, as well as reducing antibiotic usage.

Isolation of the aborted ewes, destruction of aborted material and dead lambs, and disinfection of the abortion site, is crucial to limit the spread of infection

It is also important to note that this is a zoonotic disease and therefore is a high risk for pregnant women.

Following seasons

Historically, the advice was to cull aborted ewes, but we now know they become immune once infected, however, they will continue to transmit the disease.

During the following seasons, live vaccines should be used to protect your flock.

Dealing with EAE is one of the main issues covered in our flock health club and in regular sheep meetings for clients, helping them to “plan, prevent and protect” their flock.

*Christa McMordie is a veterinary surgeon at Lisnafillan farm vets in Ballymena.

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