Cow Red Eye: Causes, When to Worry & What to Do

The most common reason a cow develops a red, watery, painful eye is infectious bovine keratoconjunctivitis (IBK), often called pinkeye. In cattle, the hallmark lesion is a corneal ulcer, which can start as a small central defect and then become cloudy or white as inflammation increases. Typical signs include squinting, tearing, conjunctivitis, and corneal opacity. Early cases may look mild from a distance, so a cow that keeps one eye partly closed deserves a closer look.

Pinkeye usually does not happen in a vacuum. The eye often becomes irritated first, then bacteria take advantage. Important risk factors include face flies, ultraviolet sunlight, dust, wind, and plant material such as foxtail or seed heads. Cattle with white faces or little pigment around the eyelids are more vulnerable to UV-related irritation. Calves are also commonly affected.

Not every red eye is infectious. A cow can also have mechanical trauma from hay, weeds, bedding, horns, fencing, or a foreign body trapped under the eyelid. These cases can look a lot like pinkeye at first. Less commonly, your vet may consider deeper corneal injury, uveitis, or other infectious causes if the eye is very painful, swollen, or not responding as expected.

Because several problems can look similar from across the pasture, it is safest to think of red eye as a symptom, not a diagnosis. Your vet can help sort out whether this is straightforward pinkeye, a traumatic ulcer, or a more serious eye emergency.

A mildly pink eye with only slight redness and no squinting may be reasonable to monitor very closely for a short period if your cow is otherwise bright, eating, and comfortable. Even then, check the eye at least daily. Pinkeye can worsen fast, especially during fly season or when several cattle are affected.

See your vet the same day if your cow is squinting hard, holding the eye shut, producing heavy tears or discharge, acting painful in sunlight, or has a cloudy cornea, white spot, visible ulcer, blood in the eye, marked swelling, or reduced vision. These signs suggest corneal damage or deeper inflammation and should not wait. A bulging eye, suspected puncture wound, severe trauma, or sudden blindness is an urgent problem.

You should also call sooner if this is happening in a calf, if multiple animals are developing red eyes, or if the cow has already been treated and is not improving. Early herd-level action matters because pinkeye can spread, and delayed care increases the chance of scarring or rupture.

While you wait for the visit, move the cow to shade, reduce dust exposure, and improve fly control. Do not put random ointments, steroid eye products, or livestock medications into the eye unless your vet has directed you to do so. Some products can worsen ulcers or complicate treatment decisions.

Your vet will start with a close eye exam and herd history. They will look for squinting, tearing, conjunctival redness, corneal cloudiness, and ulceration, and may evert the eyelids to check for a grass awn or other foreign material. In some cases, they may collect samples for culture, cytology, or molecular testing if the diagnosis is unclear, the outbreak is severe, or treatment failures are occurring.

Treatment depends on what your vet finds. For straightforward IBK, care often includes an approved systemic antibiotic, a topical ophthalmic antibiotic when practical, and pain relief or anti-inflammatory support when appropriate. In the U.S., parenteral oxytetracycline and tulathromycin are approved for treatment of IBK associated with Moraxella bovis, and oxytetracycline/polymyxin B ophthalmic ointment is also labeled for pinkeye treatment in cattle. Your vet will choose an option that fits the animal, handling setup, withdrawal considerations, and severity.

If the eye is very painful or the ulcer is deeper, your vet may recommend an eye patch, which helps provide shade and reduces fly exposure. More serious cases may need procedures such as a third-eyelid flap, temporary eyelid closure, or other corneal protection techniques. These options are not automatically necessary, but they can be very helpful when the cornea needs protection while healing.

Your vet may also talk with you about herd prevention. That can include fly control, shade, pasture management to reduce seed-head irritation, and reviewing mineral intake. Vaccination may be discussed in some herds, but response can be variable, so it is usually one part of a broader prevention plan rather than a stand-alone fix.

Home care for a cow with a red eye should focus on comfort, lower irritation, and fast follow-up. Move the cow to shade if possible. Sunlight can make eye pain worse, and shade may help a painful eye stay more open. Reduce exposure to dust, tall seed heads, and face flies. If the pasture is rough or seedy, changing paddocks can help lower ongoing irritation.

Good fly control matters for both comfort and disease control. Depending on your setup, that may include pour-ons, sprays, dust bags, rubs, manure management, or other farm-specific measures recommended by your vet. If one animal has obvious pinkeye signs, watch the rest of the herd closely because new cases can appear quickly.

Do not try to diagnose the eye yourself with leftover medications. Avoid steroid-containing eye products unless your vet specifically prescribes them, because steroids can worsen corneal ulcers. Also avoid touching the eye with dirty hands, cloths, or applicators. If your vet has already prescribed treatment, give it exactly as directed and complete the plan they recommend.

Recheck the eye every day. If redness turns into squinting, cloudiness, a white spot, swelling, or poor vision, or if the cow stops eating or seems more painful, contact your vet promptly. With eye disease, waiting an extra day can make a meaningful difference in comfort and outcome.