Outbreaks of Pinkeye that have been seen this summer are possibly due to an abundance of long grass. Pinkeye in cattle is a disease which is caused by a number of bacteria and is often precipitated by physical irritants such as dust, wind, flies and stalky grass. Also known as purulent keratoconjunctivitis, Pinkeye occurs mostly over summer but can occur at other times of the year.

The first indication of Pinkeye is the appearance of weepy eyes and sensitivity to light. This is a painful condition so cows are often seen with the affected eye partially or fully closed. Ulceration of the surface of the eye will then occur. The appearance of the eye changes, the surface colour changes to a pinky cream colour (which gives the disease its name). The centre of the cornea may also be bluish in colour.

Blindness due to Pinkeye may be partial or complete, and temporary or permanent depending on the bacteria involved, the severity of the infection, and the level of treatment.

Vaccination:
The only Pinkeye-causing bacterium which has an effective vaccine is Moraxella bovis. This is true cattle pinkeye and the vaccine is normally highly effective in preventing its spread. However, if the problem is caused by a different bacterium, the vaccination will have no visible effect at all. Almost half of swabs taken in Raglan have Branhamella ovis isolated from them; this is the cause of sheep pinkeye and vaccine isn’t protective. It does however respond to antibiotic treatment.
For this reason, it is recommended that eye swabs be taken before any treatment is undertaken to identify the cause. Once the cause is known, a decision can be made on whether or not vaccination is going to be effective. If Moraxella has been found on a property in one year, it is reasonable to presume it will still there in subsequent years. It can survive in carrier animals that show no signs, and also on objects like the rails in yards.
The usual procedure is to take swab samples and treat with antibiotics at the same time. Vaccination will be recommended if Moraxella is isolated from the swabs but individual treatment with antibiotics is recommended if other bacteria is found.
At the time of vaccination, any clinical cases should be treated with antibiotics in addition to receiving the vaccination.

Prevention:
Vaccination can stop an epidemic in its tracks. Also, if a property has had a proven Moraxella outbreak in a previous year, preventative vaccination before any cases occur is a sensible precaution. This should ideally be given at least three weeks before the main risk period begins i.e. in late spring or early summer.
Isolating infected animals can help slow down the spread of disease at the start of an epidemic, but signs can take time to develop so spotting all potentially infected animals can be tricky.
Minimising yarding of infected stock, particularly in dusty conditions, and not mixing infected and uninfected groups will also help reduce the spread. In hot weather ensuring paddocks have adequate shade so that there is less crowding of stock, and fly control will also help minimise spread of infection.

Treatment:
Treatment can be with antibiotics either directly into the eye such as with Orbenin Pinkeye syringes or systemically with injectable antibiotic such as Bivatop. Generally, injectables are only used where direct treatment is not feasible due to factors such as lack of facilities as it is more expensive but no more effective.
Treatment can be problematic due to the contagious nature of the infection, so we often supply an antibiotic spray of dilute Engemycin or Tylan to spray on the face around the eyes of all animals coming through the yards. This does seem to prevent excessive spread caused by the contact between animals at yarding. It is also a good idea to apply this spray when vaccinating in the face of an outbreak.
Minor cases of conjunctivitis not caused by Moraxella can spontaneously resolve without treatment, but pinkeye caused by Moraxella will always cause scarring of the eye and often the total loss of the eye if not treated.

Summary:
Unless you have strong evidence from past infections, individual treatment with antibiotics is the best course of action while waiting for laboratory isolation of bacteria. From past results, roughly half of cases are caused by bacteria which will not respond to the currently available vaccine.
Pinkeye in sheep seems to be a milder condition and generally self limiting. Whilst no vaccine is available for sheep, if the other prevention measures such as those mentioned above are followed and stocking density in paddocks is reduced as much as possible, specific treatment with antibiotics can often be avoided.

If you have questions regarding this article, or would like further information, please contact your Anexa Vet.