Drying-off for the spring calving cows is now fast approaching.
The primary bacterium responsible for IBK is Moraxella bovis but more recently other pathogens have also been implicated.
For clinical signs to develop, the bacteria first need to bind to the surface of the eye (the cornea) before releasing a cell toxin which causes “punch-like” holes to form in the corneal surface.
What are the risk factors?
There are a number of contributing factors for Pinkeye which can lead to “outbreaks” on some farms.
Anything causing irritation of the eye and damage to the corneal surface creates a favourable environment for Moraxella bovis.
Ultra-violet (UV) radiation is a significant risk factor and helps explain why pinkeye is more common in the summer months.
At this time other factors such as dust, pollen and seeds are also increased, causing mechanical irritation to the eye and subsequent corneal damage.
Nuisance flies peak in the summer months and promote the spread of infection between animals.
White-faced cattle or those with protruding unpigmented third eyelids are more prone to Pinkeye infection.
Some previously infected animals become ‘carriers’ in the herd, shedding the bacteria in their tears from season to season and allowing spread of infection to susceptible individuals.
What are the consequences of Pinkeye infection?
Pinkeye tends to be more common in young stock, affecting up to 80% of some herds.
The disease is very painful and can cause blindness which is temporary in most cases.
Severely affected animals may have permanent loss of sight.
There are economic losses associated with decreased feed intake, poor growth rates, reduced production in lactating cows and potentially reduced value at market.
Untreated Pinkeye can also become a welfare concern.
What does Pinkeye look like?
Initially there may only be wetting of the face due to excessive tear production from the affected eye.
This may be on one or both sides, from the affected eye down the animal’s cheek.
The eyelids will be closed; the animal may blink excessively and/or seek shade to avoid sunlight.
As the disease progresses, the surface of the eye becomes cloudy in the centre, often followed by formation of yellow pus surrounded by a characteristic pink ring.
Ulceration of the cornea is common and in severe cases the eyeball may protrude and change shape.
Treatment of Pinkeye
Early and prompt treatment results in the most favourable outcome.
Topical antibiotics are required in most cases to enable a prompt recovery with minimal pain.
In some cases an antibiotic is injected into the conjunctiva of the eye by a veterinarian and a course of injectable antibiotics may be prescribed.
Eyepatches to cover the affected eye are useful to avoid sunlight during recovery.
In extreme non-responsive cases, surgery may be required to remove the damaged eyeball.
Prevention and control of Pinkeye
Fly control is essential to help reduce the spread of infection and pour-on products registered for use in dairy animals can be used.
It is important to always read the label carefully and check for any withholding periods.
Avoidance of dusty paddocks with long grass, paddocks near bushland and excessive yarding in dry, dusty conditions will help decrease the risk of Pinkeye.
Early identification, prompt treatment and segregation of affected animals will help limit the spread of infection within the herd.
There is one registered vaccine for the prevention of Pinkeye in Australia (Piliguard, Coopers).
This is a single dose vaccine and needs to be given three to six weeks prior to the onset of the Pinkeye ‘season’.
It should be used as part of an integrated management plan for the prevention and control of Pinkeye.