Pinkeye prevention, control & management
Summer is rapidly approaching; we could really use some rain. In our area, the second cutting of alfalfa is progressing and some grass hay has been clipped. The tonnage is light, and I suspect we will see high feed prices again this winter.
We are also seeing some pinkeye cases. This seems early, but grasses are pollinating and other plants in the pastures are causing irritation.
Pinkeye is a painful eye disease that is found throughout the world. It is most common in cattle with light-colored faces and in situations with direct sunlight, dust, pollen and other environmental stressors.
Summer is the most common time for pinkeye infections. More recently, we are finding ocular problems year-round. Some feedlots have had outbreaks of what is called “winter pinkeye.”
Before an animal develops pinkeye, they typically endure a minor eye injury. These can be caused by intense sunlight, wind, dust, tall pollinating grasses and weeds, or diseases such as infectious bovine rhinotracheitis (IBR). If these injuries are not followed by a bacterial infection, the eye tears a little and then heals quickly.
Moraxella bovis is the most common cause of infectious pinkeye. These bacteria have hair-like structures which allow it to become attached to the surface of the eye. It also secretes an enzyme which erodes the corneal surface by destroying cells. The damaged cornea then turns white and opaque to protect the internal mechanism of the eye. Sometimes the cornea becomes ulcerated and the iris protrudes to plug the hole allowing the eye to maintain its shape.
Pinkeye infections may result in: a complete recovery; an opaque spot on the cornea; an eye of decreased size; or glaucoma – an enlarged or pop-eye. If both eyes are involved, blindness may occur.
Other organisms have been incriminated as a cause of pinkeye. Mycoplasma bovoculi has been cultured in the early stages of pinkeye. Its significance in the pinkeye syndrome is still not clearly understood.
Moraxella bovoculi, a sister to M. bovis, is the bacteria responsible for winter pinkeye. We send eye swabs to the South Dakota State University Diagnostic Lab and culture M. bovoculi in about half of the pinkeye cases we see. There is very little cross-immunity between the species of Moraxella. No commercial vaccine is available for M. bovoculi, so we have autogenous ranch-specific bacterins prepared from the cultures we gather. The population of Moraxella species is dynamic and constantly changing. Vaccines have helped in our practice, but they are merely a management tool and not a cure-all.
An animal’s tearing eye attracts face flies to feed on the fluids. These flies become mechanical carriers of the Moraxella organism. As they move from the eyes of one animal to another, they inoculate every eye with the Moraxella pathogen causing the disease to spread rapidly.
Broad spectrum, long-acting antibiotics have been used to effectively treat infected animals. It is best to minimize exposure of the infected eye to direct sunlight. Patches and suturing eyelids have proved effective. Treatment usually minimizes permanent lesions, decreasing market losses.
Prevention and control of pinkeye are important to herd management. Most cattle develop some immunity from previous infections, but calves, young breeding animals and herd additions (bulls), are most susceptible. Prevention efforts should be focused on those animals first. The first preventative step is vaccination with an appropriate vaccine to stimulate immunity. Control is then centered on fly control to minimize transfer between animals. Lastly, try to reduce irritation from environment stressors.
Pinkeye is a common problem in our area. Consult with your veterinarian and devise a plan specifically for your herd. Vaccination, fly control, good pasture management and early treatment is the best strategy in controlling pinkeye.
Dave Barz is a veterinarian at Northwest Veterinary Supply in Parkston, SD.