Pinkeye in cattle
Pinkeye is a constant challenge to producers during the spring and summer months, especially in younger cattle. This bacterial infection causes ulceration of the cornea and inflammation within the eye and conjunctiva (the skin surrounding the rim of the eye). Ulcers may start out small and go unnoticed for quite some time, but also cause significant pain for the animal. Permanent scarring of the cornea is possible, as well as blindness and rupture of the eye.
The causative agent for infection is known to be the bacterium Moraxella bovis, although recent research has been hinting at other bacterial causes, as well. The bacterium attaches itself to the cornea via hairlike extensions termed ‘pili.’ Ulceration typically begins at the center of the cornea and expands outward to cover the entire eye’s surface. Researchers believe that the bacteria release toxins that cause damage to the cornea and eventually develop into ulceration.
As mentioned, clinical signs of disease may be difficult to notice at first.
Cattle may demonstrate increased squinting and tearing of the affected eye. Producers often do not see these signs unless cattle happen to be in the chute at the right time. More often, affected cattle will feed less and have a decrease in weight gain as the eye becomes more painful and sensitive to strong ultraviolet light. As a result of inflammation, the eye becomes progressively cloudy and may develop blindness prior to potential rupture.
Bacteria are spread via several different mechanisms. The most common vector of importance is the face fly. Flies may be found feeding on the ocular secretions and spread the bacteria through herds by distributing infected tear fluids. Human manipulation around the eye, as well as animals rubbing faces with one another, can be a source of shared infected fluid, as well.
Researchers have occasionally been able to isolate Moraxella bovis from the nose and eyes of clinically normal cattle, suggesting that the bacterium may be a natural inhabitant in some animals – and demonstrate signs of disease when environmental conditions allow so.
Risk factors associated with pinkeye disease have been noted and include: high fly populations, dry and dusty environments, excessive ultraviolet light, lighter skin around the eyes, and nutritional deficiencies that affect the overall immune system.
Due to the high economic losses associated with pinkeye disease, reduction measures are important for your herd. Researchers (reported in JAVMA) have noted that evident ocular infections were associated with derogatory traits at postweaning selection and sale barns—both from scarring in the eyes that decreased vision, as well as lower average daily gains during infection. Vaccination is essential to preventing disease before there is a significant problem in the herd. Managers can also minimize the presence of flies and other irritants with appropriate ecto (and endo) parasiticides. When working with affected animals, proper disinfection should be conducted, such as: thoroughly cleaning instruments; hand washing; and using disposable gloves.
Treatment centers on antibiotic therapy, which can be administered as subcutaneous injections and topical applications to the conjunctiva. Some farms have also utilized antibiotics within the herd’s feeding regimen during outbreaks of disease. The only two drugs currently holding official label claims for pinkeye treatment are tularithromycin and oxytetracycline; other drugs may be helpful for treatment, but are considered “off-label” and thus require adjustments in meat and milk withdrawal times.
Prevention of pinkeye disease can be very challenging. Several simple steps can help producers manage infections and reduce risk to their herds. Insecticides should be utilized to control fly populations; both pouron therapy and insecticide impregnated ear tags have been shown to be effective. Flies have been shown to harbor the bacteria for up to three days in their regular secretions. Keeping seed heads and pastures clipped can also prevent irritants from affecting eyes during the strong windy seasons.
Any herdsmen working with animals should conduct proper hygiene practices to reduce the spread of bacteria between animals. When coming into contact with affected animals, one should consider wearing disposable gloves and using disinfectants on instruments that come in contact with infected eyes and ocular fluid. Always work with ill animals last whenever possible, in order to minimize contact with infections that are already present.
Nutrition of affected cattle should be analyzed by your veterinarian and nutritionist. Trace minerals can help promote a stronger immune system and in many cases prevent susceptibility to infections in healthy animals. Depending on your herd’s rations and grazing patterns, the level of copper and zinc are particularly important to manage.
Cattle can be vaccinated with bacterins of the Moraxella organism strain. Some producers have reported variable results with their vaccination routines. This variation is likely attributed to the several strain types that may be present in a particular herd and community, and those within the individual vaccine product. Vaccinations should be administered about a month before the fly season starts in your area, in order to allow the animal to mount an immune response, and protocol should follow manufacturer guidelines (some products will require booster doses).
Although vaccination alone may not eliminate the pinkeye in one’s herd, disease can be significantly reduced with the mentioned procedures. If problems persist, culture of an affected eye may be necessary in order to further guide treatment protocols. Setting up a routine between your herdsmen and veterinarian is critical to developing a plan that works best for your farm. — Dr. Genevieve JM. Grammer is a veterinarian working out of the Pikes Peak region. Please address correspondence to email@example.com.