Ovine Abortion Storms: Welfare in Affected Flocks

Key Facts

• Enzootic abortion (Chlamydiosis) and toxoplasmosis together account for over 60% of sheep abortion diagnoses in the UK
• Enzootic abortion is caused by Chlamydia abortus — infected ewes shed organisms at lambing, infecting naive ewes
• Toxoplasmosis (Toxoplasma gondii) is spread by oocysts from cat feces contaminating feed and pasture
• Campylobacteriosis, listeriosis, and salmonellosis cause sporadic or outbreak abortions with different management
• Vaccination against chlamydiosis and toxoplasmosis prevents the majority of cases in vaccinated ewes

Welfare Considerations

Abortion storms cause significant welfare suffering in affected ewes — the physical process of aborting fetuses is painful and exhausting, and may leave ewes with retained placentas requiring manual removal. Late abortions and weak lambs require intensive nursing care. The psychological response of ewes that lose lambs, while not fully characterized, may involve distress behaviors. Prevention through vaccination of naive ewes before their first breeding season is highly effective. Biosecurity to prevent introduction of Chlamydia and Toxoplasma to naive flocks is a core welfare responsibility.

What You Can Do

• Vaccinate naive ewes against enzootic abortion (Enzovax) before their first mating
• Control cats and prevent access to feed stores to reduce Toxoplasma oocyst contamination
• Submit aborted material for diagnostic testing — identifying the cause guides future prevention
• Isolate ewes that abort and handle aborted material with care — some causes are zoonotic
• Review flock biosecurity when buying in replacement stock — new animals may introduce infectious abortion agents