Eye diseases in sheep can be costly and if not treated properly can spread rapidly throughout a flock, says Dr Phil Scott of the University of Edinburgh.
Infectious keratoconjunctivitis (IKC), also known as contagious ophthalmia or pink eye, is often associated with adverse weather, such as high winds and driving snow during the winter months, which gives rise to the colloquial term ‘snow blindness’, says Dr Scott.
He says: “Large numbers of sheep can be affected, with competition at feed troughs and hay racks increasing the spread of infection. The condition can affect one or both eyes and in most cases can be identified by a tear-stained face. On closer examination there is marked conjunctivitis and a forced closure of the eyelids when exposed to bright sunlight. More advanced cases show severe inflammation and possibly ulceration. During late pregnancy, twin lamb disease may result in older ewes due to blindness and inability to find sufficient food.”
Affected sheep should be housed with ready access to food and water, explains Dr Scott.
“A single intramuscular injection of long-acting oxytetracycline is economically justifiable and very effective in sheep. Treatment applied straight onto the affected site cannot always be accomplished every day for three to four days under farm conditions. Immunity following infection is poor and lesions may recur.”
Provision of shelter from storms is particularly important on hill and mountain pastures, advises Dr Scott.
“Adequate trough space and feeding concentrates on the ground may limit the spread of infection. Outbreaks of infectious IKC may occur after the introduction of purchased stock, so whenever possible, these should be managed separately.”
Entropion (in-turned eyelid) is a common hereditary problem in many sheep breeds and their cross-bred progeny, Dr Scott says.
“Inversion of the lower eyelid is either present at birth or appears soon afterwards and the eye discharge quickly becomes puss-like. Direct contact between the eyelashes and cornea causes a severe inflamation, with ulceration in more advanced cases and consequent blindness. The condition frequently affects both eyes.”
The lower eyelid can be turned outwards by rolling down the skin immediately below the lower eyelid. Antibiotics applied directly to the cornea then controls potential secondary bacterial infection, says Dr Scott.
“This oily substance lubricates movement of the lower eyelid and reduces the likelihood of inversion.
"If eyelid inversion recurs after rolling out the lower eyelid, a subcutaneous antibiotic injection of 0.5ml, often procaine penicillin, is injected into the lower eyelid. A 21-gauge 15mm needle is introduced through the skin of the lower eyelid parallel to, and about 1cm below, the lower eyelid. This volume of antibiotic effectively turns out the lower eyelids and forms a depot to control possible secondary bacterial infection.
“Thin metal clips can be placed at a right angle to the eyelids and closed using fine pliers to evert the lower eyelid and can be inserted quickly by one person.”
Entropion is managed by regular inspection of all newborn lambs, ensuring their lower eyelids are normally everted, advises Dr Scott. “The genetic component of entropion should be carefully investigated and when the condition can be attributed to certain ram[s], they should be culled – but in reality this never happens.”