Pinkeye among cattle cropping up in South Dakota
Pinkeye seems to be the malady of the season, as beef producers around the tri-state area continue to report it in their cow herds, while struggling to keep the disease under control.
Pinkeye, or infectious bovine keratoconjunctivitis, is most commonly caused by the bacterium Moraxella bovis (M. bovis), though there exist multiple strains that are also capable of creating the infection. Flies carry this bacteria on their legs, where it can survive for up to three or four days. As a result, one fly can infect many animals.
Several environmental factors are required for the development of the disease. First, eye irritation is necessary. Cattle which lack pigmentation around the eye are more susceptible because this allows increased ultraviolet radiation (sunlight) to sensitize and inflame the eye. Irritation also occurs when cattle graze in pastures containing tall grass and weeds which rub and poke at the eyes as the animal reaches to get at newer grass below. This rubbing causes lesions to form on the eye. At this point, flies discover the injury and begin to feed on the secretions, further damaging the eye while also shedding M. bovis into the affected area.
Early signs of pinkeye include swelling and redness of the eye, tearing or watering and squinting against the sunlight. The eye may become opaque or cloudy, and the center of the cornea (the clear outer layer) may develop an ulceration. Severe ulceration, corneal rupture and permanent blindness may result, although infrequently. More often, complete recovery occurs, with only a few affected eyes having a persistent white scar on the cornea.
The economic impact of pinkeye is significant. Infected cattle do not gain well and milk production is decreased. Discounted prices at sale time can be expected. Add to these the cost of treating animals, and it’s easy to see how many dollars can be lost.
As with any disease, pinkeye prevention is preferable to treatment. Insecticide ear tags help control face flies, as do the use of back rubbers, dust bags and pour-ons. A vaccine is available which contains killed M. bovis bacteria. For this reason, two injections of the vaccine for calves and yearlings are usually better than one since it stimulates better antibody production. It should be noted that younger animals are more susceptible than older ones because they lack previous exposure and therefore the acquired immunity that older animals often have.
If pinkeye infection is already present, aggressive treatment steps are necessary. Commercial sprays are on the market which can be applied topically to the eye. These kill the bacteria on contact and do not further irritate the eye, but due to tearing they get flushed out and are not as effective.
M. bovis is highly susceptible to antibiotics such as oxytetracycline, penicillin and sulfonamides. Long-acting oxytetracycline injected intramuscularly seems to be quite effective, especially when a repeat dose is given in 72 hours.
Patches are also available commercially to cover the infected eye, protecting it from flies and further exposure to sunlight. Cement the patch over the eye with the adhesive provided, or use pieces of old cloth such as denim with your own skin-safe adhesive. Sunlight will disintegrate these patches in about a week – usually more than enough time for the eye to heal.
Rob Hunsaker of the Hunsaker Cattle Company near Fairburn, SD recently treated pinkeye in part of his herd. He used all three methods described above; some animals received only spray, some received only antibiotic, and the most severe cases received spray, antibiotic and patches. At that time approximately 20 percent of his cows and 30 percent of his calves were affected. Three days later the cattle were reworked, and about half of the infection had cleared up, with only two or three new cases. Cattle pastured in another location remain unaffected.
Why the apparent increase in pinkeye in certain areas? As Roy Hendrickson, Practice Manager at the Animal Clinic of Rapid City, South Dakota explained, “This is a year in which all the necessary environmental factors are present. Many regions experienced an unusually wet spring and early summer, encouraging continual grass growth. That now tall grass has dried out, becoming stemmy and irritating to the eyes of cattle grazing it. Additionally, also due to the early wet weather, there is an increased fly population.”
Abundant tall grass and more flies has made pinkeye a real issue for cattlemen in the area.
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