Spring always brings surprises! Early in calving I received a call out to an adult dairy cow with some unusual clinical signs. The day before her owners had noted a bit of a head tilt, and that she seemed to be consistently circling to the left, combined with her lack of appetite and the fact that she had recently calved, she had initially been treated as a metabolic cow. When this treatment did not resolve the circling, we were promptly called in for a look. In addition to the circling and head tilt, we also noted that she had mild facial paralysis on the left side, with a droopy eye and lip.
Neurological diseases are many and varied and can cause a wide range of clinical signs depending on the area of the brain which is affected, however the combination of circling, inappetence, and one sided facial paralysis is fairly characteristic for one disease in particular – Listeriosis.
Listeria monocytogenes is a hardy bacteria which is widespread in the environment, found in both soil and faeces. Soil contamination of feed is often the source of infection, cases are often associated with the feeding of poorly fermented grass silage. The low pH of well fermented grass silage inhibits the growth of Listeria, however even good silage can have areas of break down (often indicated by mouldy spots!) and Listeria can easily multiply in these patches.
Infection occurs via small wounds in the mucous membranes of the mouth or nose. Once in the body, the bacteria invade the nerve roots of one of the major nerves originating from the brain, called the trigeminal nerve and uses it as a highway up to the brain itself. This causes a meningitis, and the associated clinical signs.
Classic signs of listeriosis include:
The incubation period for infection is usually 2 weeks or longer before clinical signs start to show. Listeria infection can also cause abortions, and a condition known as “silage eye”.
Treatment involves good supportive care, anti-inflammatory pain relief, and a long course of high dose penicillin. Prognosis varies depending on how long the cow has shown clinical signs, and the areas of the brain which are affected.
