It shows up every year and to the unlucky cattle that contract what is commonly called pinkeye, it is incredibly painful and if left untreated, can lead to loss of the eye, says K-State Research and Extension veterinarian Larry Hollis.

Pinkeye, known to veterinarians as Infectious Bovine Keratoconjunctivitis or IBK, usually is caused by the bacteria Moraxella bovis, Hollis says. “However, we’ve found that in many cases — especially the extremely difficult cases — another bacteria, either Branhamella ovis or Mycoplasma bovoculi, is also present.”

The disease is spread by flies, and Hollis stresses that good fly control around cattle production areas should always be a priority. Pinkeye is often at its worst in late summer and early fall, he adds, because the fly population has had time to build through the summer.

The disease can be relatively easy to treat in its early stages but can accelerate rapidly, and if not treated aggressively can lead to damage to the eye or complete loss of the eye.

“It is painful as all get-out,” Hollis says, and cattle with an active case of pinkeye or those with permanent damage are discounted at sale time. “Watch for animals that are producing an unusual amount of tears that show up on the face,” he says. “There will always be a carrier animal in the vicinity — either in your herd or one down the road.”

Those who suspect pinkeye should look into the eye closely for any ulceration on the cornea. In extreme cases the cornea will appear white because of pus buildup inside the eye.

Cattle with pinkeye are extremely sensitive to light — even on a cloudy day. “If you’re got a few cattle that are hanging back in the shade while the rest go out to graze, even on days with cloud cover, you very well may have a pinkeye problem,” Hollis says.

Tall pasture grasses also can contribute to the spread of pinkeye late in the season. The tall grass or seedheads can irritate cattle’s eyes as they graze, and once the eye starts tearing in response to irritants, flies are attracted to the discharge, some of which may be carrying the Moraxella bovis bacteria. “Tears are like a magnet for flies,” Hollis says.

Oxytetracycline is often effective in treating individual animals with pinkeye, he adds, but he encourages producers to call their veterinarian about the best treatment options.