Cattle on spring pasture

Editor’s note: The following was written by Russ Daly, South Dakota State University Extension veterinarian, for the Extension website May 22.


Have you ever thought about how some years get labeled “bad years” for a certain animal disease? We remember that “bad year” for calf scours.

What is it about those “bad years”? Are there years when there are just a lot more germs around for some random reason?

The reasons behind cattle diseases exploding in certain years and not others have to do with the fact that our animals are beholden to their environment. Climatic conditions such as snow, rain, heat or humidity can affect the ability of the animal to resist a certain disease or succumb to it.

Cattle are among the domestic animals most affected by our fickle weather conditions here in the Northern Plains.

Plentiful moisture during the grazing season might contribute to what could be called a “bad year” for a certain cattle disease: pinkeye.

Not unfamiliar to cattle producers, 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, it can lead to blindness.

Different types of germs have been identified in affected eyes, with Moraxella bovis being the one most commonly found.

So what creates a potentially “bad year” for pinkeye? Again, it’s not simply because there are more germs around. 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.

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, causing more irritation. Even strong sunlight provides an irritation that the bacteria can take advantage of.

Pinkeye tends to affect multiple cattle in a herd. When the bacteria is 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 fly control, 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 do what they can to protect cattle from this painful, production-robbing disease.