Pinkeye, also known as infectious bovine keratoconjunctivitis (IBK), is one of the most common diseases of beef cattle in Virginia. It is a highly contagious disease, causing inflammation of the cornea (the clear outer layer) and conjunctiva (the pink membrane lining the eyelids) of the eye. It will also cause ulceration, which looks like a hole or depression in the cornea. The incidence of pinkeye increases in spring, peaks in the summer, and decreases in the fall. Pinkeye results in mild to severe disease and, in approximately 2 percent of the cases, will cause blindness.
Pinkeye is of major economic significance to producers, a significant cost is lost yearly to pinkeye through decreased weight gain, decreased milk production, and treatment costs.
Affected animals may also bring significantly discounted prices at sale. In a 20-year review study, calves diagnosed with pinkeye weighed 19.6 pounds less at weaning than healthy calves, while another study showed the loss to pinkeye to be 36 to 40 pounds at weaning.
Also, it is estimated that a calf that is blind will gain 60 pounds less by weaning time compared to healthy calves. Animals blind in both eyes are also at risk of death through accident or starvation if they are unable to locate the feed and water sources. Pinkeye is the most common condition affecting breeding age beef heifers, and the second most common disease of nursing calves greater than three weeks old.
Causes of Pinkeye
The primary infectious agent for pinkeye is the bacterium Moraxella bovis. This bacterium is found in the eyes of many recovered and apparently normal cattle. Pinkeye is a multifactorial disease, which means there are many factors that predispose and contribute to the development of the disease.
Eye irritation is necessary for the development of the disease. Face flies, which look like large houseflies, feed around the eyes and nostrils of cattle, causing a mechanical irritation to the eye and spreading the disease from one animal to another. The bacteria can survive on the flies for up to four days, so many animals may be infected by one fly.
Other sources of eye irritation are tall weeds and grasses rubbing the eyes as cattle walk and graze, and feed and dust when cattle eat from overhead feed bunks or the center of round bales. Dust on windy days, and exposure to excessive UV sunlight also increase the chances of disease development. Breeds which lack pigment on their eyelids are more susceptible to pinkeye because of their increased sensitivity to sunlight and a decreased immune response in the eye.
Calves are more likely to develop the disease than adult cattle, as adult cattle appear to develop protective antibodies on the surface of the eye. Bull calves have a higher incidence of disease than heifer calves.
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