Pinkeye, also known as infectious bovine keratoconjunctivitis (IBK) is a highly contagious disease, causing inflammation of the cornea (the clear outer layer) and conjunctiva (the pink membrane lining the eyelids) of the eye. Pinkeye results in a mild to severe infection and can cause blindness in approximately 2 percent of the cases. It has a major economic impact affecting cattle through decreased weight gain, decreased milk production, and treatment costs.
Pinkeye is a multifactor disease, which means there are many factors that predispose and contribute to the development of the disease. The primary infectious agent for pinkeye is the bacterium Moraxella bovis. This bacterium is found in the eyes of many recovered and apparently normal cattle.
Eye irritation is necessary for the development of the disease. This irritation can be caused by many risk factors including dust, pollen, weeds, UV sunlight, compromised immunity, and light skin around the eyes. These irritations may cause the eye to water and secrete mucus, which face flies feed upon.
Face flies feed around the eyes and nostrils of cattle, causing a mechanical irritation to the eye and spreading the disease from one animal to another. The bacteria can survive on flies for up to four days, so many animals may be infected by one fly. Other sources of irritation are tall weeds and grasses rubbing the eyes as cattle walk and graze, or feed and dust when cattle eat from feed bunks or the center of round bales. Dust on windy days, and exposure to excessive UV sunlight also increases the chances of disease development. Breeds which lack pigment on their eyelids are more susceptible to pinkeye because of their increased sensitivity to sunlight and decreased immune response in the eye.
As with many diseases, the disease outcomes can be influenced by nutritional imbalances, such as deficiencies of protein, energy, vitamins (especially vitamin A if the forage is lower quality), and minerals, (especially copper, selenium and zinc). The presence of other organisms such as the IBR virus, mycoplasma, Chlamydia, and Branhemella ovis will increase the incidence and severity of the disease.
Transmission occurs when a non-infected animal comes into contact with secretions infected with M. bovis. This may be direct contact, through face flies, or contact with an inanimate object that harbors the organism. Face flies are one of the primary vectors for spreading the bacteria and disease.
Management practices that reduce the risk factors associated with pinkeye are the most effective tools in decreasing the incidence of the disease.
Fly control is essential, but can be difficult as face flies are only on the animal for a small percentage of the time. Therefore, addressing the egg and larval stages of the fly as well as the adults is most effective. A moderate to heavy fly infestation is when there are 10 to 20 face flies per animal during the middle of the day. A single fly-control program will not work on every farm, so it often takes multiple methods of control to achieve good results. Fly tags, insecticide pour-ons, back rubbers, dust bags, and knock-down sprays are helpful in reducing the number of adult face flies on the animal. Feed additives such as IGR’s (Insect Growth Regulators) are available that target the larvae that are laid in the manure. Encouraging dung beetles, which break down the manure pat, will also decrease egg survival.
Face flies can develop resistance to pesticides over time, so switching the drug class of the pesticides used every year is important. For example, if pyrethrins are used one year, then organophosphates should be used the following year. Try to keep all pesticide classes with the products used the same throughout the year. Waiting until the start of fly season to apply fly tags and removing the old fly tags in the fall also decreases the development of resistance. It is also important to read the label of various fly control products to determine if it is approved for use within certain classifications of cattle, such as lactating dairy cattle, dairy heifers, and beef cows, along with any identified withdrawal periods for meat and milk consumption.
Appropriate grazing and weed control will help reduce the irritation to the eyes for all classes of cattle, as well as reducing the resting areas for the flies. Shaded areas need to be available to decrease the UV exposure.
Minimization of transmission of the M. bovis bacteria is essential as you treat infected animals. Use new disposable gloves every time, for every animal, while disinfecting any instruments that come in contact with infected eyes or eye fluids between animal treatments. Change clothing after treating infected animals, before working with healthy animals. These things will also help decrease the spread of the bacteria from infected animals to healthy animals.
Utilization of a vaccination program for Pink eye should be done in consultation with your veterinarian. There are many different strains of the M. bovis bacteria and determining which vaccine is appropriate for your herd is essential to maximize protection. It is important to remember that if you are going to use a vaccination program that the vaccines should be administered at least six weeks prior to the fly season in order to develop adequate immunity.
Animals with a strong immune system are less susceptible to pinkeye infections. Trace mineral and vitamin programs are important to promote a healthy immune system. You should work with your veterinarian to determine the appropriate nutrient needs for your herds. This will vary by geographic area and by the types of forages your cattle are consuming.
In summary, a good preventative program for pink eye will include fly and dust control, minimization of exposure to UV light, appropriate sanitation methods, weed control, appropriate pasture grazing management, an appropriate vaccination program, good quality nutrition, and minerals available at all times will decrease the incidence of this disease occurring in your herd.