Dave Sparks
Vet Link
Is pinkeye stealing your beef cattle profits?
Any cattleman who hasn't had a serious episode of eye problems in his cattle can put it on his list of things to look forward to. This syndrome is properly called infectious bovine keratoconjunctivitis, which translates to an infection that causes inflammation of the surface of the eye and the tissues surrounding the eye in cattle.
Pinkeye can affect cattle of any age, but it is much more of a problem in young cattle, because they haven't yet had the opportunity to develop immune system resistance to it. Although cases can occur any time of year, it is more prevalent in the summer because that is the time of greatest irritation and the time for the presence of vectors. Although pinkeye is never fatal, it results in very significant economic losses due to costs of treatment, poor performance, and, in some cases, decreased value of blind calves.
The infection is primarily due to the bacteria Morexella bovis, but other bacteria can also be involved. Respiratory virus infections, particularly IBR (infectious bovine rhinotracheitis), can be part of the picture by either causing an inflammatory eye condition that predisposes the animal to the more severe bacterial infection, or by acting as secondary invaders that make bacterial damage even worse.
Although an organism acts as the causative agent, several conditions contribute to the syndrome. Animals with compromised immune systems due to either poor nutrition or chronic debilitating disease are more susceptible.
Physical irritation is important as it sets up an environment in the eye for the organism to thrive. Sources of irritation include ultraviolet light (UV light), dust, plant or hay materials and flies. Flies are a two-edged sword because they not only contribute to the irritation of the eye, but also serve as vectors to carry the bacteria from one animal to another. Animals that overcome the syndrome without treatment can remain as carriers for up to one year, thereby carrying the problem forward from one year to the next to be spread to susceptible animals.
Course of the problem
The course of the problem is fairly rapid. Within two or three days from the onset, an opaque area is noticed on the surface of the eye and the tissues around the eye become reddened and swollen. The eye weeps or tears excessively, and one or both eyes may be involved. The animal usually stands with the eye closed due to pain caused by exposure to UV light. This discomfort seriously reduces grazing time, and weight loss follows. By Day 6 the surface of the eye is entirely opaque, causing blindness, and on close examination, deep ulcers can be seen on the cornea. If untreated, the condition can last for four to eight weeks.
Treatment options
Eventually, resolution comes in one of three forms. Most animals will eventually heal with no permanent damage, but after severe economic loss. Some animals will heal, but with varying degrees of white scarring on the cornea. In some cases the cornea ruptures, resulting in a cone-shaped bulging of the eye structures and permanent blindness.
Treatment is usually effective and dramatic. A subcutaneous injection of long-lasting oxytetracycline at the labeled dose, repeated in 48 to 72 hours, will clear the infection and eliminate the carrier stage, thus reducing the spread to other animals.
It is important to treat as early in the course of the disease as possible. If it is treated early, the limited amount of tissue damage heals fairly quickly. If allowed to progress until ulcers are formed, pain and damaged tissues persist much longer.
In years past, another popular treatment was to use nitrofurazone sprays or powders applied directly to the eye. While effective, this should no longer be practiced because nitrofurazones have been banned for use in food animals.
Healing can be facilitated by using patches over the eye to keep out irritants such as flies, light and dust. Suturing the eyelids together for a few weeks not only keeps irritants out of the eye but also provides structural support that may help prevent the eye from rupturing. Your local veterinarian can advise you on this procedure.
With pinkeye, as in many other syndromes, an ounce of prevention is worth a pound of cure. Fly control is perhaps the most important preventative measure. Shade should be provided so that animals can find relief from UV light during the brightest part of the day. If shade is too limited, however, it can actually be detrimental by causing the animals to group tightly and allowing for increased spread of the organisms from animal to animal by flies or by direct contact of eye secretions. Replacement animals should be selected from animals with pigment around the eyes where possible.
If seedheads are tall, causing cattle to graze down through them, clipping them off is helpful. Do not feed hay overhead, or where animals can eat back into the bale. A good virus disease vaccination program will help reduce the incidence and the intensity of pinkeye outbreaks. Oral tetracycline in mineral feed can help to control the bacterial infection. Although several pinkeye vaccines are available, they may or may not be helpful because there are many different strains of M. bovis and because of the many other factors involved in the disease process.
No silver bullet
There is no silver bullet for pinkeye. No single management practice will eliminate the concern. Instead, control depends on understanding the several factors involved, such as bacteria, vectors, irritants and immunity. By incorporating consideration of these factors into your overall management you can minimize the effects of pinkeye on your animals and on your profitability. An excellent fact sheet on pinkeye is available from your OSU Extension Office.