Enzootic abortion of ewes, caused by Chlamydia abortus, is the most common infectious cause of sheep abortion in the UK and much of Europe. Vaccination programmes dramatically reduce pregnancy losses and the significant welfare cost of late-term abortion storms.
Ewes aborting in the last two weeks of pregnancy have carried lambs to near term, representing weeks of physiological investment followed by abrupt pregnancy loss. Late abortion causes retained placenta, metritis, and in severe cases septicaemia. The welfare cost of an abortion storm — where dozens of ewes abort within weeks — includes both individual animal suffering and significant flock-level productivity loss. Welfare-centred prevention requires vaccination of all naive female sheep before first mating, strict biosecurity at lambing, prompt isolation of aborting ewes, and staff awareness of the human health risk.