Plentiful moisture during the summer might contribute to what could be called a "bad year" for bovine pinkeye.

Pinkeye is a bacterial infection of the surface of the eye. What starts out as red, weepy eyes quickly progresses to severe inflammation and an eating-away of the clear portion of the eyeball. It's a painful problem for affected cattle. Left untreated, pinkeye can lead to blindness.

What makes a potentially "bad year" for pinkeye?

Researchers tell us that pinkeye germs can be found in the eyes of normal cattle. What's more, when they try to artificially create the disease experimentally, they can't do it by just squirting the bacteria in the calf's eye. It's not just the germ; there has to be something more.

That something more is irritation. The normal eye is very good at resisting infection. In order to cause infection and inflammation, pathogenic bacteria have to stick to the eye surface, multiply, and release enzymes that damage the cornea. But this surface is constantly washed by tears, which also contain antibacterial substances. Simple blinking also brushes bacteria off the cornea. Even if some of the bacteria happen to stick, the cells of the cornea (the clear portion of the eye) turn over every five to seven days.

But, irritation to the eye surface is just the chink in all this armor that Moraxella is waiting for — and the opportunities are plentiful during moist summers.

Tall grass can scratch the eye surface, and pollen is an additional irritant. Flies and other insects become more plentiful, and they are particularly drawn to tears and gunk that forms in the corner of the eye, which causes more irritation. Even strong sunlight provides an irritation that the bacteria can take advantage of.

Because bovine pinkeye can't easily be replicated by simple exposure to the bacteria, it could very well be considered an environmental disease. Reducing the pinkeye risk for pasture cattle means addressing their environment.

The role of the bacteria should not be entirely discounted, however. Pinkeye tends to affect multiple cattle in a herd. When the bacteria are successful at infecting an animal, there's more of it around to spread to another by flies or direct contact. Exposure to higher bacterial numbers means less of an irritation is needed for an infection to start.

It's easier said than done, but controlling the environmental aspects of pinkeye through controlling flies, providing shade and clipping tall grass should be considered. While the success of pinkeye vaccines is erratic, they should also be discussed with your veterinarian. Just because the environmental aspects of pinkeye may be hard to control, producers should still should do what they can to protect cattle from this painful, production-robbing disease.

More information
Good overviews of pinkeye can be found in the following iGrow articles:

• Early Detection recommended this summer

• Think about pinkeye Prevention for the Coming Summer

Daly is the South Dakota State University Extension veterinarian and the State Public Health Veterinarian