NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare.

Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.

Silage Eye (Bovine Iritis)

NADIS data shows that last December there was a significant increase in the number of cattle with bovine iritis (more commonly known as silage eye). The seasonality of this disease does vary from year to year but the bulk of cases occur between January and April.

What is silage eye?

Silage eye is an eye infection caused by the bacterium Listeria monocytogenes, also commonly associated with the brain disease listeriosis. It is primarily associated with the feeding of silage (which explains its common name and the time of year in which it occurs), in particularly big bale silage. The proportion of cattle affected is very variable (from 10 to 80% of a group), with higher proportions predominating

Despite having been described in outbreak form 16 years ago very little is known of this disease and it has not been reported in outbreak form outside of the UK and Ireland. It is commonly associated with big bale silage, but can occur in cattle fed clamp silage. Bovine iritis is a disease where early recognition is essential as early treatment and prevention can significantly improve animal welfare and reduce the disease’s economic impact, so its important to recognise and distinguish bovine iritis from New Forest eye.

Clinical Signs

1) Profuse eye discharge: Originally clear, becoming sticky and purulent

2) Temporary blindness

3) Bluish opacity of the surface of the eye (the cornea), which can become yellow as pus develops

4) Bulges in the iris, with white discolouration.

5) Very painful, especially when eye is examined

A cow showing the typical signs of bovine iritis. Note the bluing of the cornea with the accumulation of white material below the eye surface of an intact cornea. Unlike New Forest eye there is no ulcer. Also note that the third eyelid at the corner of the eye is pale pink; i.e. there is no conjunctivitis.

Treatment

Systemic or sub-conjubctival treatments are much more effective than antibiotics applied directly onto the eye. Ask your vet for advice on treatment

Prevention

Silage eye occurs for two reasons:

1) The silage is contaminated with Listeria during its production (usually from soil) and this is not killed during fermentation (which is why big bale silage is more commonly associated with silage eye)

2) The feeding of the forage is associated with eye damage as the animals compete for food

Thus prevention has two main strands

a) Minimising the feeding of potentially contaminated silage, either by feeding clamp silage rather than big bale, or by minimising the soil contamination at harvest