Michael Metzger, Michigan State University Extension Educator
(Previously published on MSU Extension, Sheep & Goat: November 17, 2023)
Listeriosis is a disease that can affect all ruminants as well as other animal species and humans.
Listeriosis is an important infectious disease of sheep and goats most commonly causing encephalitis, but also capable of causing a blood infection and abortion. The organism can be shed in milk from an infected carrier animal as well as sick animals which has a risk of infecting humans.
Listeriosis is caused by the bacterium Listeria monocytogenes and is commonly seen in cooler climates. These bacteria can be found in the soil, food sources, the gut, and feces of healthy animals. Most commonly, this disease of sheep and goats is observed as a result of feeding moldy or spoiled hay or silage that has not been properly fermented. It’s possible for your sheep and goats to become infected without feeding moldy or spoiled hay or silage as the organism is commonly found in the environment.
Common sources of contamination
- Silage not fermented (not acidified) properly, put up too dry, or not compacted tight enough to protect it from the air
- Round bales of hay that have started to rot
- Feed bunks that are not cleaned regularly and in which some feces and wet feed leftover accumulate and ferment
- Rotting (decaying) woody debris
- Milk, urine, and drainage of the eyes and nose of infected animals
Environmental and fecal contamination are more common sources of the disease than silage in sheep and goats because most are never fed silage. Michigan State University Extension recommends not using silage for small sheep flocks and goat herds as the silage could spoil before they are consumed and possible Listeriosis infections can result.
Symptoms of Listeriosis include depression, loss of appetite, fever, lack of coordination, salivation, facial paralysis, and circling. The abortion form of Listeriosis usually shows no other symptoms and can only be diagnosed by laboratory analysis. The onset of the encephalitic form is usually very fast and causes death in 24-48 hours after symptoms appear. Affected animals may have a droopy ear, drooping eyelid, and saliva running from limp lips on one side of the face caused by a partial paralysis. When near death, the animal will lie down and may have convulsions. A diagnosis can only be confirmed in a diagnostic laboratory, but isolation of the organism can be difficult. The listeriosis organism is easily killed by common disinfectants.
Recovery is rare but is possible with early aggressive antibiotic treatment and supportive care of the affected animals. Large doses of Oxytetracycline or Penicillin G may help in some cases. Producers must consult their veterinarian as treatments require off-label drug usage.
Steps for prevention or to minimize associated risks
- Not feeding spoiled feeds
- Recently introduced animals should be considered suspect as carriers and should be quarantined before mixed them with the herd or flock
- Infected or suspicious animals should be isolated from the rest of the herd or flock
- Floors, pens, sheds, feed bunks, mineral feeders, etc. should be thoroughly cleaned on a regular basis and disinfected with a disinfectant
- If several animals are affected and silage or round bales of hay are being fed, their use should be discontinued until they can be ruled out as a source of contamination. Care should be taken when handling suspect animals
Although listeriosis is a deadly infectious disease of sheep and goats, it is easily preventable by not feeding spoiled feeds and proper cleanliness on the farm.