Wednesday, 29 August 2018

How to control enzootic abortion in ewes with vaccination


Lis King, AHDB Sheep Scientist, discusses the measures farmers can put in place to proactively
control enzootic abortion in their flock.

Globally, there is an urgent need to slow the development of drug resistant bacteria in both human and veterinary medicines. The sheep industry has been tasked with reducing antibiotic use in three areas: new-born lambs, lameness and abortion. Sheep farmers can plan ahead, prevent disease occurring and protect their animals whilst doing their bit for the environment. All whilst saving time and money. A win for all.

The most commonly diagnosed cause of abortion is Enzootic Abortion of ewes (EAE) which is infectious and responsible for around 50 per cent of sheep abortions in the UK. Yet, it is preventable through a highly effective single vaccine which lasts the lifetime of the ewe.

EAE is caused by the bacteria Chlamydia abortus. Generally there are no symptoms, with the first sign being a premature stillborn lamb one to two weeks before the expected lambing date. However, the disease can also result in full-term stillborn or weak lambs and can affect litter mates to different degrees, for example; one can be dead and one alive.

Ewes that abort can contaminate pasture or bedding and the bacteria is then picked up by other ewes. Aborted ewes should be promptly isolated for at least three to four weeks with bedding, aborted material and dead lambs destroyed.



The cost of abortion is variable but estimates are around £85 per aborted ewe so any abortion should be thoroughly investigated. A simple laboratory test will diagnose EAE. Treatment with long-acting oxytetracycline antibiotic will reduce the risk of further abortions but should only be given once EAE is confirmed. If left untreated, infected ewes and surviving ewe lambs, are more than likely to abort in the next pregnancy. Once a flock has the disease it may persist in these carrier sheep.

It’s often thought that using antibiotics to treat abortion, without any diagnosis, is cheaper than vaccination. However, a one off vaccine, which equates to around £2-3 is less than the cost of repeated antibiotic treatments. So switching to vaccination to control enzootic abortion could put an end to whole-flock antibiotic treatment of ewes in late pregnancy. 

All ewes must be vaccinated at least four weeks before they go to the ram, as options to vaccinate in-lamb ewes can be limited. Three vaccines are currently available in the UK: MSD’s Enzovax, CEVA’s Chlamydia and Benchmark’s Mydiavac. If unsure, discuss with your vet about what would be most suitable for your flock. 



Any flock that buys in replacement ewes is at risk of introducing EAE and should vaccinate for prevention rather than risk the expense of disease. Together with robust biosecurity measures, changing to vaccination can reduce lamb losses, maximise ewe productivity across your flock and reduce antibiotic use. A win win situation!

For more information see the BRP manual, Reducing lamb losses for Better Returns or check out our infographic.



You can also follow the online conversation by using the hashtag #VaccinesWork from 8 September and get involved with helping the agricultural industry to reduce antibiotic usage. For more information, you can visit www.ruma.org.uk