Infectious Bovine Keratoconjunctivitis (Pinkeye)
Infectious bovine keratoconjunctivitis, commonly called pinkeye, is a contagious bacterial eye disease. This disease spreads rapidly and causes economic losses. A 1993 study estimated U.S. losses of $150 million from decreased weight gain, milk production, and treatment. Pinkeye was second to scours as the most prevalent condition affecting unweaned beef calves over 3 weeks old in 1996, according to the 1997 report of the National Animal Health Monitoring System of the USDA: APHIS: Veterinary Services. Pinkeye (1.3% infection rate) and footrot (0.8% infection rate) were the two most prevalent conditions affecting all breeding beef females (replacement heifers and cows), according to the same report. Young stock are most susceptible to pinkeye, but the disease may be found in cattle of all ages. Many older animals may have a natural immunity to pinkeye because of previous exposure. Pinkeye is most frequently found in grazing and feedlot cattle. Summer herd outbreaks involving up to 80% of young cattle and lasting 3 to 4 weeks are common.
Pinkeye is characterized by a reddish inflammation of the eye ball, swollen eye membranes (the conjunctiva), tearing, frequent blinking, and sensitivity to light. A white raised or ulcerated area appears on the center of the eye ball within 1-2 days. Left untreated, the entire cornea becomes thickened and opaque, resulting in a white color and blindness. The ulcer on the cornea may penetrate to the eye interior, and the eye may even rupture. Body condition loss and severe pain are common. On rare occasions, severely infected cattle stop eating and die of starvation.
The main cause of the infectious pinkeye syndrome is the bacterium Moraxella bovis. Tear secretions in cattle appear to be deficient in an enzyme that kills bacteria (lysozyme). Recent work has shown that infected carrier animals may be a major source of infection. A carrier is an animal that may or may not have suffered from pinkeye in the past and may show no outward signs of disease. Nevertheless, in the presence of a number of predisposing factors, this animal is still able to spread the M. bovis bacterium.
High numbers of face flies (Musca autumnalis) are associated with higher rates of pinkeye. These flies cluster at the edge of the eyes to feed on tears and are very irritating to cattle’s eyes. Face flies also carry and transfer the bacteria M. bovis from infected to non-infected animals. The house fly (Musca domestica) and the stable fly (Stomoxys calcitrans) also may spread pinkeye infections.
Other contributing factors include eye irritants such as ultraviolet sunlight, dust, mechanical irritation from seeds, tall pasture grasses, awns on small grain seed heads, and dust. Rough forages such as fescue, hybrid Sudan grass and other forage sorghums mechanically irritate the eyes. Weeds and brush produce air-borne irritants, pollen and chaff, as well as serve as mechanical irritants. The incidence of foreign body irritation is greatly increased when animals eat out the middle of round bales, leaving a hay shelf over their heads. The same situation occurs when hay is fed in overhead feeders. This is especially true with hay made from small grains.
Recent field surveys have shown the incidence and severity of pinkeye varies among and within breeds of cattle. Cattle with pink eyelids (such as Hereford and Hereford crosses were more susceptible to pinkeye than Angus, Charolais and dark-faced breeds, possibly because more ultraviolet rays enter the eye. . Some researchers recommend that only bulls with fully pigmented eyelids be used as herd sires since eyelid pigmentation is moderately heritable (26 -34 percent).
Pinkeye is often confused with the presence of a foreign body in the eye, physical injury or other diseases. Early cases of cancer eye and Infectious Bovine rhinotracheitis (IBR) can look like pinkeye. Veterinarians are best able to recognize and differentiate cattle eye disease problems. The veterinarian will also provide professional advice regarding the treatment of pinkeye.
Carefully follow all treatment advice and prescription label instructions. Recheck all withdrawal times with your veterinarian. A veterinarian – client – patient relationship is necessary for the use of all prescription drugs and “off-label” prescriptions (drugs used at dosages and for purposes other than defined on the label).
Using over-the-counter aerosol sprays and powders often further irritates infected eyes. These products cause increased tear secretion that washes away the antibiotic. Eye drops or ointments are better alternatives for mild or early cases of pinkeye. They are non-irritating and do not result in excessive tear secretion. Repeated doses are necessary to sustain adequate drug levels. Most strains of M. bovis appear to be sensitive to tetracyclines, penicillin, erythromycin and neomycin. The bacterium is usually resistant to cloxacillin (commonly found in dry cow mastitis ointments). Injection of a mixture of antibiotics such as penicillin, streptomycin or gentamycin, under the lining of the affected eyelids is recommended in herd outbreaks where repeated treatments are impractical. Often one injection is sufficient, but the treatment will need to be repeated in three or four days for severe or advanced cases of pinkeye. An intramuscular treatment is generally not recommended because very high dosages of an antibiotic are required to ensure adequate levels of the drug reach the eyes and tear glands.
Treatments for severe corneal ulceration include performing eye surgery to protect the affected eyeball from further injury and promote healing, or creating a 3rd eyelid flap or the gluing of protective plastic covers onto the skin around the eyes to avoid further eye irritation. Consult your veterinarian for assistance in these methods to enhance the healing process. In addition to medical treatment, good management and nursing care is required to bring about full recovery. General recommendations include: housing in shaded areas (to avoid direct sunlight); provision of adequate feed and water; reduction of dust, flies and other physical causes of eye irritation.
While many optical antibiotics are available for pinkeye, treatment is not always successful in saving vision. Success depends on finding and treating cases early in the course of the disease. Complete recovery may take 3 to 5 weeks. Since face flies both carry the bacteria that causes pinkeye from one animal to another and irritate the eye, fly control is extremely important once pinkeye has been diagnosed. Spraying cattle with a fly knockdown spray will reduce new pinkeye cases.
The best protection against pinkeye is prevention. Vaccination against pinkeye is economically justified if the vaccine protects against multiple strains. Fly control is an important part of a pinkeye prevention program. Tall grasses can be kept short through pasture management, to prevent eye irritation while the cattle are grazing.