Pink eye in cattle starts with excessive tearing and a watery discharge from one or both eyes, then progresses to a cloudy or white spot on the surface of the eye that can develop into a visible ulcer. Formally called infectious bovine keratoconjunctivitis (IBK), it’s one of the most common eye diseases in beef herds and can look quite different depending on how far it has progressed.
What Early Pink Eye Looks Like
The first thing you’ll usually notice isn’t the eye itself but the animal’s behavior. Affected cattle squint, blink excessively, and try to stay in shaded areas because their eyes become sensitive to light. You may see wet streaks running down the face from heavy tearing, and the membranes around the eye will look red and swollen. At this stage, the cornea (the clear surface of the eye) still looks relatively normal, which makes early cases easy to miss from a distance.
Within a day or two, a small white or grayish spot appears near the center of the cornea. This is the beginning of an ulcer. The eye continues to water heavily, and the discharge may turn thicker and more yellow. The conjunctiva, the pink tissue lining the eyelids, becomes noticeably inflamed and puffy. Cattle at this point often hold the affected eye partially or fully closed.
How the Eye Changes as It Progresses
If left untreated, that small white spot expands into a larger ulcer that can eventually cover much of the cornea. The eye takes on a distinctly cloudy or bluish-white haze as inflammation spreads across the surface. Blood vessels begin growing inward from the edges of the cornea toward the ulcer, giving the eye a pinkish-red rim that gradually creeps toward the center. This blood vessel growth is actually part of the healing process, but it signals significant damage.
In severe cases, the ulcer deepens enough to cause the cornea to rupture. When this happens, the eye collapses inward, the internal structures may protrude, and the animal loses vision in that eye permanently. Even eyes that heal without rupturing can develop a permanent white scar on the cornea, which may or may not affect the animal’s sight depending on its size and location. The entire progression from first tearing to deep ulceration can happen in as little as a week under bad conditions.
What Causes It
The primary culprit is a bacterium called Moraxella bovis. It attaches to the surface of the eye using tiny hair-like structures called pili and then produces toxins that destroy corneal cells, creating the ulcers you see. Another species, Moraxella bovoculi, is frequently isolated from affected eyes, but researchers have not been able to reproduce typical pink eye lesions with it alone in experimental settings. M. bovis remains the clearest proven cause.
The bacteria alone aren’t always enough to trigger disease. Eye irritation is a necessary precursor. Face flies are the biggest contributor: they feed on secretions around the eyes and nostrils, mechanically irritating the eye surface while carrying bacteria from animal to animal. Tall grass and weeds with seed heads scratch the cornea as cattle graze. Dust on windy days, feeding from the center of round bales, and prolonged UV exposure all weaken the eye’s defenses and set the stage for infection. This is why pink eye outbreaks peak in summer, when flies, sunlight, and tall pastures all converge.
How to Tell It Apart From Other Eye Problems
Several other conditions can make a cow’s eye look abnormal, and telling them apart matters because the treatments differ. Infectious bovine rhinotracheitis (IBR), a viral disease, can cause red, watery eyes that look similar at first glance. The key difference is location: IBR-related corneal changes tend to appear along the outer edge of the eye, while IBK ulcers form near the center of the cornea. IBR also typically comes with respiratory symptoms like nasal discharge and coughing.
Bovine malignant catarrhal fever, another viral disease, produces eye inflammation along with prominent respiratory signs and fever. The eye involvement tends to affect deeper structures rather than the corneal surface. Squamous cell carcinoma, sometimes called “cancer eye,” creates raised, irregular growths on the eye or eyelid that look nothing like the smooth, cloudy ulcers of pink eye, though early stages of cancer eye can occasionally be confused with chronic irritation. A veterinary exam is the most reliable way to distinguish these conditions.
Reducing the Risk in Your Herd
Fly control is the single most impactful prevention strategy. Face flies spread the bacteria between animals, so reducing their population with ear tags, pour-on treatments, dust bags, or back rubbers directly limits transmission. Keeping pastures clipped to prevent seed heads from developing reduces mechanical irritation to the eyes. Providing shade, whether from trees or constructed shelters, cuts UV exposure that weakens the cornea’s surface.
Vaccines exist for pink eye, but the evidence for their effectiveness is underwhelming. A five-year randomized trial compared a commercial vaccine, a custom-made (autogenous) vaccine tailored to the specific bacteria on a given operation, and a placebo. The autogenous vaccine produced the lowest disease rate at 24.5%, compared to 30% for the commercial vaccine and 30.3% for the placebo, but the difference was not statistically significant. The autogenous vaccine did trigger a stronger antibody response, with about 81% of calves showing a measurable immune reaction versus 63% for the commercial vaccine. Yet higher antibody levels did not correlate with actual protection from disease. Vaccination alone is not a reliable shield against pink eye, though some producers still use autogenous vaccines as one layer of a broader prevention plan.
What Treatment Looks Like
Catching it early makes a significant difference in outcomes. Cattle with early-stage tearing and small corneal spots respond much better to treatment than animals with deep ulcers. Treatment typically involves an injectable antibiotic prescribed by a veterinarian. Some producers also use eye patches to shield the damaged cornea from sunlight and flies during healing, which reduces pain and can speed recovery.
Separating affected animals from the herd limits spread, since face flies will carry bacteria from an infected eye to a healthy one within minutes. Treated cattle should be monitored for improvement over the following days. If the ulcer continues to worsen or the animal needs retreatment, that may indicate a more resistant infection or a deeper ulcer requiring more aggressive intervention. Most uncomplicated cases heal within two to three weeks with appropriate treatment, though the white scar on the cornea can take longer to fade and may remain permanently in severe cases.
Which Cattle Are Most Vulnerable
Calves and young cattle tend to be hit hardest, partly because they haven’t built up any natural immunity from prior exposure. Cattle with light-colored faces and non-pigmented eyelids are more susceptible because they lack the natural UV protection that darker pigmentation provides. Herds on open pastures with no shade, heavy fly pressure, and tall grass face the highest risk. Overcrowding also increases transmission, since it puts more eyes within range of the same flies and concentrates bacteria in a smaller area.