Sheep Listeriosis: Silage-Associated Disease

Listeriosis in sheep is a serious bacterial disease often associated with poor-quality silage causing encephalitis and septicemia with significant welfare and production implications.

Key Facts

Listeria monocytogenes causes three main disease forms in sheep: encephalitic, septicemic, and ocular
Encephalitic listeriosis causes circling, head tilt, facial nerve paralysis, and inability to eat or drink
Poor-quality silage with pH above 5.5 is the most common source of Listeria on farms
The bacterium multiplies in aerobically spoiled or poorly fermented silage
Disease often occurs in winter when silage feeding is at its peak
Mortality rates are high even with antibiotic treatment unless caught very early
Zoonotic risk exists particularly for pregnant women handling infected animals or silage

Welfare Considerations

Listeriosis encephalitis causes severe neurological impairment in affected sheep. Circling animals are unable to navigate normally, may fall and be unable to rise, and cannot access food or water without assistance. The disease is distressing and rapidly progressive. Treatment requires intensive nursing including hand feeding and watering, positional management, and high-dose antibiotic therapy. Prognosis is poor for many affected sheep and humane euthanasia is appropriate for those unable to stand or swallow. Prevention through good silage management is far more effective than treatment.

What You Can Do

Ensure silage is made with adequate fermentation including correct dry matter and additives where needed
Monitor silage pH and discard any batches with poor fermentation or visible spoilage
Remove spoiled silage from clamps before feeding and avoid offering moldy or aerobically compromised feed
Inspect sheep daily during silage feeding periods for early neurological signs
Seek veterinary treatment promptly for any sheep showing circling or facial nerve signs
Isolate and nurse affected sheep with access to food and water positioned to allow swallowing
Practice good hygiene when handling Listeria-affected animals particularly in pregnant household members