Abortion Storms in Sheep: Welfare and Management

Infectious Abortion in Sheep: A Major Welfare Event

Infectious abortion outbreaks — or 'abortion storms' — represent one of the most significant welfare events in sheep farming. When an infectious cause spreads through an unprotected flock, abortion rates can reach 30% or more, causing widespread suffering, farmer distress, and significant economic losses. Understanding causative agents and implementing preventive protocols are essential welfare priorities.

Major Causes

Enzootic Abortion (Chlamydiosis): Caused by Chlamydophila abortus, enzootic abortion is the most common cause of sheep abortion in the UK. First-time infection typically occurs in the last few weeks of pregnancy, causing late abortions, stillbirths, and weak lambs. Infected ewes shed bacteria at lambing, spreading to susceptible animals. Vaccination is highly effective.

Toxoplasmosis: Toxoplasma gondii infection causes early embryonic death, mummification, and abortion depending on stage of gestation at infection. Cats are the definitive host; oocysts contaminate feed and pasture. Good hygiene and vaccination (Toxovax) reduce risk significantly.

Campylobacteriosis: Campylobacter jejuni and C. fetus cause sporadic and epidemic abortions. Associated with introduction of infected animals or exposure to contaminated water. Outbreaks can affect up to 50% of ewes in naïve flocks.

Listeriosis: Listeria monocytogenes causes abortion, encephalitis, and septicaemia. Associated with poorly fermented silage with high pH. Feeding good quality silage is the primary prevention.

Border Disease: Persistent infection with Border Disease Virus causes reproductive failure, hairy shaker lambs, and congenital abnormalities.

Welfare Impacts

Beyond pregnancy loss, affected ewes experience pain, uterine infection risk, and metabolic stress. Ewes may require intensive veterinary support. Surviving lambs from infected dams may be weak, requiring extensive nursing. The concentration of abortions at lambing time creates significant workload stress for farmers.

Management During an Outbreak

• Isolate aborting ewes immediately; collect aborted material for laboratory diagnosis
• Increase shepherding intensity to identify affected animals
• Maintain strict hygiene — many agents are zoonotic (transmissible to humans)
• Seek prompt veterinary advice on antibiotic treatment (effective for chlamydiosis, campylobacter)
• Support affected ewes with nutritional supplementation
• Submit samples for definitive diagnosis to guide vaccination strategy

Prevention Strategies

Vaccination against enzootic abortion and toxoplasmosis is the cornerstone of prevention. Blood testing replacement stock before introduction, biosecurity protocols for purchased animals, cat control around feed stores, good quality silage management, and maintaining closed flock policies where possible all reduce abortion storm risk.

Zoonotic Risk

Several abortion-causing agents pose serious risks to pregnant women: Chlamydophila abortus, Coxiella burnetii (Q fever), Listeria monocytogenes, and Campylobacter spp. Pregnant women should avoid contact with aborting ewes and lambing ewes entirely. Clear farm signage and strict hygiene protocols protect farm visitors and workers.

This page is part of the Animal Welfare Hub — providing evidence-based information to improve the lives of animals. Return to home.