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Dr Jakob Malmo
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 Pinkeye can affect cattle of all ages, but it is primarily a disease of calves. At times we do see considerable numbers of milking cows in a herd affected.
The outbreaks of pink eye are highest during the summer months, partly because of greater exposure to sunlight and flies. One of the problems associated with this disease is weight losses of as much as 0.25 kg per day in calves with pinkeye.
Moreover, calves may be left with scars on the cornea – these may make affected cattle more difficult to handle and may be subject to discounts when they are sold.
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Cause of pinkeye
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The primary infectious bacteria is Moraxella bovis. The surface of the bacteria is covered by hair-like structures known as pili, which attach or adhere to the conjunctiva or the cornea. Adhesion prevents the bacteria from being washed away by tears and blinking.
Unpigmented eyelids and white hair on the face do not absorb ultraviolet light, which in turn increases the susceptibility of the calf to the organism that causes pinkeye. Another factor that increases the susceptibility of the calf to pinkeye is irritation of the eye by dust or plant material from mature pastures. Also, flies can carry the bacteria from one calf to another.
The pinkeye bacteria are shed in the tears or discharges from the eye of infected cattle. Carrier animals, shedding the causative organism of pinkeye, can remain infected for over a year, and can provide the source of the infection from year to year. The conjunctiva of the eye of susceptible cattle is the portal of entry for the bacteria carried by contaminated dust, tall grass, direct contact, or flies.
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Signs of pinkeye
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Initially, the eyelid is swollen, and large amounts of watery tears flow from the eye. Sensitivity of the infected eye to light causes the animal to seek shade or refuge in a darkened shed. The centre of the cornea appears white in a day or two; this is followed by corneal erosions and ulcerations. The entire cornea of one or both eyes may be involved within six days after the first tearing is observed.
As an outbreak progresses, the disease frequently intensifies as the virulence of causative organism increases in the spread among susceptible calves. Some animals recover with no permanent damage to the eye. Some have a permanently scarred cornea but retain a degree of sight. A few are blind in one or both eyes.
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Prevention and treatment of pinkeye
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Recommended management practices for reducing the incidence and severity of pinkeye include:
Avoid grazing cows on long mature pasture so as to reduce irritation of the eyes and to reduce contact with plant material contaminated with the tears of affected calves.
Control of flies with fly control procedures such as applying Arrest.
Treatment of individual animals should be initiated early to prevent permanent damage to the eye. Treatment in early cases simply requires the administration of an ointment such as Orbenin Eye Ointment into the affected eye.
If a number of animals are affected, consideration should be given to having a veterinarian inject appropriate antibiotics into the eyelid under the first layer of the conjunctiva (the 'white' of the eye). Usually only one treatment is required, and response to treatment is generally good.
Severely affected eyes can be treated by covering the eye with an eyepatch or suturing the lids shut after the eyelid conjunctiva has been injected with antibiotic.
Prevention is the best approach, but if cases do occur early treatment can minimise losses associated with pinkeye.
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Dr Jakob Malmo
Maffra Veterinary Centre
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