Pinkeye in Cattle
Pinkeye is a highly contagious infectious disease affecting the eyes of cattle. The name describes the redness and inflammation of the lining of the eyelid and eyeball, an early sign of the disease. This common disease can vary in its severity from year to year.
Although pinkeye rarely causes the death of affected cattle; it can cause substantial losses to the cattle industry through decreased weight gain, lowered milk production and treatment costs. Pinkeye is known to occur at all seasons of the year and in all breeds of cattle. Pinkeye can occur in one or both eyes. Excessive weeping of the affected eye and closure due to pain are the two signs most commonly observed. As the disease progresses, the cornea becomes cloudy or white. An ulcer frequently develops near the center of the cornea. Blood vessels often extend into the cornea from the white of the eye as the healing processes begin. Cattle with pinkeye keep the affected eye or eyes closed because of pain and to avoid bright sunlight. The course of the infection may run for 4 to 8 weeks, or even longer.
As the eye begins to heal, white scar tissue infiltrates the cornea. In most cases this scar will gradually disappear as healing progresses and vision will be restored. However, in severely affected eyes, a white scar often persists and interferes with vision. If the ulceration is severe enough to penetrate all layers of cells forming the cornea, the fluid in the eyeball will escape. This results in the iris and/or lens protruding partially or entirely through the ulceration. If this occurs, there will be permanent blindness in the affected eye.
Pinkeye is primarily caused by Moraxella bovis (M. bovis) however veterinarians have also found that Mycoplasma bovoculi and IBR virus are capable of causing an eye infection resembling pinkeye. Other factors instrumental in causing eye irritation, thereby allowing for invasion of M. bovis and subsequent disease, are excessive ultraviolet light (sunlight), the face fly, the house fly, the stable fly, plant material and dust. Plant material such as cool and warm season grasses, hybrid Sudan grass and other forage sorghums, weeds and brush produce air-borne irritants, pollen and chaff, as well as serve as mechanical irritants. When animals eat out the middle of round bales, leaving a hay shelf over their heads, the incidence of foreign body irritation is greatly increased. The same situation occurs when hay is fed in overhead feeders. This is especially true with wheat hay or hay containing cheat grass.
The face fly has been associated with an increased incidence of pinkeye in recent years. Research at the University of Nebraska's West Central Research and Extension Center has demonstrated that face fly feeding produces mechanical injury to the conjunctiva and spreads IBR virus and Moraxella bovis from animal to animal as the fly feeds on eye and nose secretions of cattle. Flies not only serve as irritants as they feed on secretions from the eye; they also serve as a means of transmitting M. bovis from infected to non-infected animals. Face flies can remain infected with M. bovis up to 3 days following feeding on infected material. Under experimental conditions, disease transmission is uncommon without the presence of face flies and is common with flies present. The infection can also be spread by direct contact when the eye secretions of an infected animal are rubbed into the eye of an uninfected animal.
Vitamin A deficiency and inadequate protein intake may be other factors that possibly contribute to lessened resistance to eye infections. Vitamin A deficiency results in excessive watering of the eye, night blindness, and may cause cloudiness of the cornea in severe cases, giving the eyeball a dry, lusterless appearance.
Pinkeye is caused by a combination of factors. Dry, dusty environmental conditions or wet, warm environmental conditions play a role. In wet, warm conditions such as many parts of Nebraska experienced this year can lead to overgrowth of pastures. The taller grass and seedheads can damage the eyes. The wet, warm conditions also lead to heavier fly populations that irritate the eyes and spread the organisms.
A good control program should incorporate procedures to reduce initial eye irritation. An intensive fly control program is essential to limit the spread of pinkeye in a herd of cattle. Cattle often have grass or weed seeds in their eyes, and these materials no doubt irritate the eye and contribute to the development of pinkeye. Cattle with pinkeye can be helped by prompt treatment. Since the cornea heals slowly, any ulceration is likely to require several weeks for complete recovery. There are medications available for treating pinkeye. However, many of the most effective pinkeye treatments must be recommended by a veterinarian with whom you have a valid veterinary-client-patient relationship. This is because the medications are only available by prescription or because the dose or route of administration is not on the label. Also, at least a part of the decision on how to treat pinkeye is what kind of restraint is available and how frequently cattle can be treated. There are other infections that look like pinkeye so it is recommended that you consult with your veterinarian to assist you in the diagnosis and treatment of pinkeye.
[June 3rd, 2010]
Richard Randle, Associate Professor, Vet & Biomedical Sciences
University of Nebraska - Lincoln, Lincoln, NE