Preventing pink eye in cattle comes down to controlling three things: the flies that spread it, the environmental irritants that damage the eye’s surface, and the nutrition that keeps eye tissue resilient. Infectious bovine keratoconjunctivitis (IBK) is one of the most common and costly eye diseases in beef and dairy herds, but a layered prevention strategy can dramatically reduce outbreaks.
What Causes Pink Eye in Cattle
The primary culprit is Moraxella bovis, a highly contagious bacterium that attacks the cornea. A second species, Moraxella bovoculi, is frequently isolated from the eyes and nasal passages of affected animals and likely plays a supporting role. These bacteria produce a toxin that destroys corneal cells, leading to the characteristic ulcers and cloudiness.
The bacteria can’t easily infect a healthy, intact cornea on their own. They need help getting in. That help comes from mechanical damage to the eye’s surface caused by UV light, dust, wind, pollen, tall grass, and plant awns. Once the outer layer of the cornea is compromised, bacteria colonize and multiply rapidly. Face flies are the primary vector, feeding on eye secretions and carrying bacteria from infected animals to healthy ones across the herd.
Control Face Flies Aggressively
Face flies are the single biggest transmission route. They feed on the tears and secretions around cattle eyes, picking up bacteria from infected animals and depositing them on the next animal they visit. The economic injury threshold is 10 to 15 face flies per face. If your cattle are at or above that number, you need active intervention.
Insecticide-impregnated ear tags are the most common tool, but their effectiveness against face flies is limited compared to horn flies. In controlled trials, ear tags with 10% permethrin reduced face fly numbers by about 49% over eight weeks, while tags with lower concentrations provided no significant control. Face fly reduction across all tag treatments averaged less than 50%. That means ear tags alone won’t solve the problem. You’ll get better results by combining tags with other methods: back rubbers or dust bags placed where cattle pass through daily, pour-on insecticides, and feed-through fly control products that prevent larvae from developing in manure.
Remove ear tags at the end of fly season. Leaving them in year-round accelerates insecticide resistance in fly populations, which makes future control harder.
Reduce Environmental Irritants
Anything that scratches or irritates the cornea opens the door for infection. Tall grass and seed heads are a common culprit. When cattle graze through mature pastures, plant awns contact the eye surface and create micro-abrasions. Clipping pastures before seed heads mature, or rotating cattle out of tall stands, reduces this risk significantly.
Dust is another major irritant, particularly around feeding areas, working facilities, and dry lots. Watering down dusty areas during dry spells helps, as does placing hay feeders and mineral stations in locations where dust doesn’t accumulate. Wind compounds the problem by driving dust and pollen directly into cattle’s eyes, so windbreaks or sheltered feeding areas offer some protection.
UV light from direct sunlight damages corneal cells, making them vulnerable to bacterial invasion. Cattle with less pigmentation around their eyes, such as Herefords and other white-faced breeds, are especially susceptible because unpigmented skin allows more UV radiation to reach the eye. Providing shade structures in pastures gives cattle a way to limit their UV exposure during peak sun hours. When selecting replacement animals, favoring those with pigmented eyelids is a long-term genetic strategy that pays off over generations.
Maintain Adequate Vitamin A Levels
Vitamin A is essential for maintaining the health of epithelial tissues, including the outer surface of the eye. It supports immune function, cellular repair, and the integrity of mucous membranes. When cattle are deficient, those protective barriers weaken and become more susceptible to infection.
Deficiency is most common in cattle fed dry, preserved forages over extended periods. Fresh green pasture is rich in beta-carotene (which cattle convert to vitamin A), but hay loses much of its beta-carotene content during curing and storage. In one study of cattle with confirmed vitamin A deficiency, blood levels were dramatically below normal, with a median of 49 mcg/L compared to a reference range of 130 to 380 mcg/L. Clinical signs of deficiency typically appear when levels drop below 200 mcg/L.
If your herd relies on hay or silage for a significant portion of the year, supplementing with a vitamin A source through mineral mixes or injectable supplements keeps levels in the protective range. A good free-choice mineral program that includes vitamin A is one of the simplest and most cost-effective steps you can take.
Isolate Infected and New Animals
A single infected animal can seed an entire herd through fly transmission and direct contact. Pulling affected cattle out of the group as soon as you spot tearing, squinting, or corneal cloudiness limits how many flies can pick up bacteria and spread them. House isolated animals in a shaded area away from the main herd, and treat them promptly.
New arrivals are another risk. Cattle can carry Moraxella bacteria without showing symptoms, particularly in nasal passages. Quarantining new animals for 21 to 30 days before introducing them to the herd gives you time to observe for signs of disease and reduces the chance of bringing in a carrier. Work with your veterinarian to set a quarantine period based on your herd’s specific disease risks.
What About Vaccines
Vaccination is a logical tool, but the results have been inconsistent. Multiple studies evaluating both commercially available and autogenous (custom-made) vaccines administered by injection have reported a lack of efficacy against pink eye. One study found numerically lower infection rates in cattle vaccinated with a custom vaccine containing M. bovis, M. bovoculi, and Mycoplasma bovoculi antigens, but the difference was not statistically significant.
Part of the challenge is strain variation. The bacteria in your herd may not match the strains in a commercial vaccine. Autogenous vaccines, made from bacteria isolated directly from your own herd’s outbreak, theoretically offer a better match, but even these haven’t shown reliable protection in controlled trials. Intranasal delivery routes are being explored as a way to stimulate local immunity at the eye and nasal surfaces, though this approach is still being evaluated.
Vaccination can still be part of your program, especially if your herd has recurring outbreaks, but it should never be your only line of defense. The physical prevention strategies of fly control, irritant reduction, nutrition, and isolation consistently deliver more reliable results.
Putting It All Together
Pink eye prevention works best as a system, not a single intervention. Before fly season begins, make sure your mineral program includes adequate vitamin A. Deploy fly control measures (tags, dust bags, pour-ons) when face fly counts approach 10 to 15 per face, and combine at least two methods for better coverage. Clip pastures before seed heads mature. Provide shade. Quarantine new arrivals. And monitor your herd daily during peak season so you can pull and treat affected animals before they become sources of infection for the rest of the group.
Herds with white-faced genetics deserve extra attention across all of these categories. The combination of unpigmented eyelids and high UV exposure makes breeds like Herefords disproportionately affected. If pink eye is a persistent problem in your operation, selecting for eyelid pigmentation in your breeding program is one of the most effective long-term decisions you can make.