Bovine Iritis – ‘Silage eye’
Bovine iritis, also known as ‘silage eye’, appears as a bluish-white cloudiness in the eye, with a red angry rim at the junction of the sclera and cornea (where the white and black parts of the eye meet). Silage eye is extremely painful as demonstrated by excessive tearing and closing of the eyelids.
Treatment includes subconjunctival injection of antibiotic and steroid. Topical cloxacillin (Orbenin Ophthalmic ointment) can also be used in early cases.
The causal agent is the bacteria Listeria monocytogenes, which is widespread in the environment. Silage eye is most commonly associated with feeding big bale silage. Listeria are more likely to grow in big bales compared to clamp silage due to their lower density and higher DM content, which results in a slower rate of fermentation. Bales also have a high surface area to volume ratio, so more of the silage will be exposed to air if the wrap becomes damaged. Listeria thrive in the presence of air, even if the pH is low.
Affected silage may not always be visibly mouldy. The risk of Listeria surviving in big bale silage can be reduced by ensuring that air is excluded for the duration of storage and feeding big bales immediately upon opening.