Infectious bovine keratoconjunctivitis (IBK), more commonly known as pinkeye, is one of the most common diseases of cattle, especially during the summer months. It is a highly contagious disease that causes inflammation of the cornea and conjunctiva of the eye. It can lead to ulceration of the cornea, giving the classic appearance of the white depression or ulcer that many cattle producers describe. Pinkeye results in mild to severe disease, and can cause blindness in an affected eye.
Pinkeye has a major economic impact to producers, as an estimated $150 million is lost yearly through decreased weight gain, decreased milk production and treatment costs. Affected animals generally bring decreased prices at sale. In one study, calves diagnosed with pinkeye weighed nearly 20 pounds less at weaning than healthy calves, while another study showed a 36 to 40 pound difference in weaning weight.
The primary cause of pinkeye is the bacteria Moraxella bovis. This particular bacterium is found in the eyes of both healthy and infected eyes. Pinkeye is multifactorial; that is, many factors predispose and contribute to the development of the disease within an individual. Eye irritation is necessary for pinkeye to develop. Face flies, which feed around the eyes and nostrils of cattle, cause mechanical irritation to the eye and spread bacteria from one animal to another. M. bovis can survive on flies for up to four days, so many animals can be infected by one fly. Other sources of eye irritation are tall weeds and grasses rubbing the eyes as cattle graze, and feed and dust when cattle eat from overhead bunks or the center of round bales. Exposure to UV sunlight due to lack of shade also can increase the chances of pinkeye. Breeds of cattle with white pigment around the eyes (Hereford, Charolais, Hereford crosses, Holsteins) are more susceptible to pinkeye probably due to increased sensitivity to sunlight. The presence of other infectious agents such as IBR virus, Branhemella ovis, mycoplasma and Chlamydia will increase the incidence and severity of the disease.
Treatment is most successful when started at the first signs of disease. Injectable oxytetracycline is generally effective, but many other antibiotics such as penicillin, ceftiofur, florfenicol and tularythromycin are also very effective. Treatment with a long acting medication is most effective and less labor intensive. More advanced cases will benefit from injection of an antibiotic and dexamethasone under the bulbar conjunctiva of the affected eye. I would recommend this be done by your veterinarian. With large groups of animals, such as weaned calves or cows on pasture, the addition of feed additive antibiotics such as AS 700 or Aureomycin can help decrease the severity of cases. Work with your vet to determine the most effective treatment options for your animals.
While there is no guaranteed way to eliminate all cases of pinkeye, there are many things producers can do to decrease the number and severity of pinkeye cases. First and foremost is fly control. Multiple modes of fly control, including fly tags, pour-ons, sprays, back rubbers and dust bags all can decrease fly contact with cattle. Because the fly does not need to spend much time on the animal to transmit M. bovis, control of larval hatches may be the most beneficial control method. Many products in the form of feed and mineral additives are available. These products work by treating the manure with chemicals that inhibit the hatching and development of new flies. For this method to work, the additives need to be started before fly season begins.
Pasture management is another method to decrease irritation to the eye. Clip pastures when seed heads appear and clip weeds down as they develop later in the summer. If you feed round bales, spread bales out on the ground rather than feeding in round bale feeders. Vaccines are available, but their efficacy is debatable. In some herds, they are effective in reducing cases; in other cases, no difference in case rate is seen even after vaccination.
Mike Bloss, DVM, owns Countryside Animal Clinic with his wife, Kirstin Bloss, DVM, in Aurora, Mo.
