Winter Pinkeye in Cattle
Livestock Update, January 2000
W. Dee Whittier, Extension Veterinarian, Cattle, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech
Pinkeye disease in cattle occurs most often in the summer but may be an important disease in the winter as well. Because it is associated with summer grazing producers may question the diagnosis of pinkeye in the winter. This may lead to inappropriate or unnecessary treatments or preventive approaches.
Pinkeye begins as a small hole or ulcer in the clear part of the eye (the cornea). The affected animal is uncomfortable so it tends to hold the eye closed and often has increased tear production as well. While some cases heal at this point many develop into more complicated cases. The ulcer often grows in size, allowing fluids to enter the cornea and giving the eye a cloudy appearance. Cattle often become blind in the affected eye or eyes. Complications include eye perforation, inflammation of the internal eye parts resulting in a "pop eye" or prolonged healing with large scars.
Pinkeye tends to occur more in the summer because eye defenses are weakened by sunlight and irritation from flies, dust and plants and their pollen. The bacteria that causes the disease is also spread by flies, especially the cattle face fly.
Pinkeye can occur in the winter as well. Cattle confinement in the winter can provide for spread of the bacteria between animals. This may especially happen when cattle have intimate contact at the feed bunk or a watering trough. Animals that have recovered from pinkeye often become long-term carriers, shedding the bacteria from their nasal secretions. When the secretions from carrier cattle contact the eyes of non-immune cattle the disease may result. If eyes are less resistant due to irritation from feed or because of nutritional deficiencies cases of the disease may result more frequently. Once a first case occurs huge numbers of bacteria from diseased eyes present a threat to other cattle. An outbreak affecting a large percentage of cattle may occur. Calves tend to have less immunity than older cattle so outbreaks in stocker or backgrounding cattle are most frequent.
A disease that may be falsely suspected when winter pinkeye occurs is Infectious Bovine Rhinotracheitis or IBR. IBR causes an inflammation of the pink tissue surrounding the eye (the conjunctiva) but does not tend to cause ulcer formation. IBR also infects the respiratory tract as well in nearly all cases. Cattle with IBR should have fevers, nasal discharge and coughing. Many cattle with IBR develop pneumonia.
In some cases producers experiencing outbreaks of pinkeye have falsely assumes the disease is IBR and makes the decision to vaccinate against IBR. This can make an outbreak worse if the vaccine used is the modified-live type (MLV). This occurs because the virus in the MLV vaccine, while not causing disease in most cases still invades the cells of vaccinated cattle. Because eye cells are also invaded they are made more susceptible to invasion by the pinkeye organism.
Pinkeye is a disease that continues to be a frustration for cattle owners in Virginia because neither preventive nor treatment procedures are uniformly effective. Vaccination has not been totally satisfactory as a preventive. Decreasing exposure by controlling flies is quite effective in preventing summer pinkeye outbreaks. Timely treatment and isolation of cattle that develop pinkeye in the winter are the most effective preventive actions.
Treatment of pinkeye is done by injection an approved antibiotic containing tetracycline. The approved products are long-acting products so only a single treatment is needed. Early treatment not only is more effective but also stops organism shedding sooner thus reducing the risk to other cattle.