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Vet's View: Preventing and treating eye diseases in sheep

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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. 

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Infectious keratoconjunctivitis

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.”

Treatment and prevention

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

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.”

Treatment and prevention

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.”

More information

For information on anterior uveitis and periorbital eczema, visit www.nadis.org.uk/bulletins/eye-diseases-in-sheep.aspx

Top tips for vaccinating sheep

  • Equipment: The tool used to administer vaccines largely depends on the number of animals to be vaccinated and the route of administration. A vaccination gun is recommended. It allows proper cleaning of the needle between each sheep, eliminating the risk of contaminating the remaining vaccine
  • Needles: Subcutaneous vaccines need a 20 gauge, 0.9mm by 15mm (0.6 inch), needle. A 20 gauge, 0.9mmby 25mm (1in) needle is used for intramuscular vaccines
  • Site of injection: The package insert will indicate the site of injection and for subcutaneous vaccination this is generally on the side of the neck four inches back from the ear. For intramuscular vaccination, the neck muscle in front of the shoulder is usually suggested
  • Replacements: Needles should be replaced after every 15 to 20 injections. If using single-use syringes, it is critical the needle used for injecting the sheep is not reintroduced into the vaccine vial. Instead, leave a sterile needle inserted into the bottle and withdraw further doses through this. 
  • Preparation: The package insert will provide instruction on preparing the vaccine prior to use. Some must be shaken, some should be warmed and some need to be reconstituted with a provided solvent
  • Administering: On no account should different vaccines be mixed together in the same syringe although some may be given while the sheep is already on another vaccine programme. Some vaccines are rendered ineffective while others can even cause harm if they are given concurrently or within a certain time frame of antibiotics or other medicines. This may be stated on the packaging but if you have any doubt, refer to your supplier.

 

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