Summertime means many opportunities for cattle to enjoy the pasture, but it’s also peak season for pinkeye. We asked veterinarians Michaela Kristula and Billy Smith of the University of Pennsylvania’s New Bolton Center about the disease, which is most often caused by the bacteria Moraxella bovis.

1. How do flies come in contact with the disease, Moraxella bovis?

Any irritation to the eyes lets Moraxella bacteria invade the eyes and cause pinkeye. Face flies play an important role in the spread of pinkeye. The face flies irritate the eye, causing discharges (both tears and mucus). The flies feed off the discharges and pick up the Moraxella species. Bacteria from infected eyes can spread the bacteria to other calves on the farm or even nearby farms.

2. Other than flies, what are irritants that can cause pinkeye?

The most important control method involves maintaining an environment that is free of irritants. Any damage to the eye will let Moraxella bacteria adhere to the surface of the cornea and cause damage. Control methods to prevent irritation to the eyes involve controlling face flies, mowing tall grass and weeds, limiting dust, providing space by reducing overcrowding and providing shade to protect the eyes from harmful UV rays from the sun that can increase tear production.

3. Are white-faced cattle more susceptible? What is the reason for that?

White-face cattle such as Herefords and Charolais with less pigmentation around the eye are more sensitive to sunlight.

4. Can nutritional deficiencies in vitamins or minerals play a role in a bovine’s susceptibility?

Having a good vaccination, parasite and nutrition program are important to maximize herd immunity. The nutrition program should include proper levels of protein, energy, forage, vitamins (i.e. vitamin A), and trace minerals such as selenium and copper. The vaccination program should include the respiratory viral diseases IBR, PI3, BVD and BRSV.

5. Is pinkeye more common in spring and summer versus fall and winter?

Most cases of pinkeye occur in the spring, summer and fall. In our practice we see the most cases during the summer. The summer is the season most associated with the increase in the number of irritants such as flies, dust, tall dry grass pastures and sunlight.

6. Is having pinkeye in the winter a possibility?

Pinkeye can also occur in the winter. Risk factors for the winter are irritation to the eyes caused by close confinement, feed, UV light reflected from the snow and viruses such as IBR that can cause tearing.

7. What are some of the first clinical signs of pinkeye?

The first clinical signs are excessive tearing, discharge, blinking, squinting and redness of the eyes. The cattle and calves will seek shade because the sunlight is irritating. The next stage is formation of an ulcer at the center of the cornea that appears as white spot. A toxin produced by the bacteria causes cell damage and death leading to the formation of an ulcer. Left untreated the cornea becomes cloudier and the ulcer can progress to cover the whole cornea and eventually even rupture the eye.

8. What treatment is available for pinkeye?

Early detection and treatment of animals when the first clinical signs (tearing, blinking) appear is critical to limiting the damage to the eye. We recommend using both long-acting systemic antibiotics and topical treatment. Approved systemic antibiotics for pink eye include long-acting tetracycline (LA 200®, Biomycin 200®) and tulathromycin (Draxxin®). The systemic antibiotics are helpful because their long duration of activity and concentration of drug in the tear film of the eye can eliminate the bacteria from the eyes. Topical treatment involves either injecting procaine penicillin with dexamethasone under the conjunctiva (subconjunctivally) of the eye or applying ointments labeled for eye application. We also recommend applying a fly repellent to the face and an eye patch to the treated eye as this will provide extra protection and likely decrease the spread. If possible, segregate affected cattle from non-infected cattle.

9. What are some steps farmers can to take to prevent pinkeye?

The best strategy is to work with your local veterinarian and put a comprehensive plan in place to prevent, control and treat pinkeye. In addition to having a good herd health program in place to maximize herd immunity, other important factors are to maintain an environment that is free of irritants and to design a comprehensive face fly control program. This could involve placing insecticide impregnated ear tags prior to the fly season, using insecticide pour-ons, dust bags and feed additives that target maggots (fly larvae) in the manure. Early detection and treatment of pinkeye is critical.

10. Can this kind of pinkeye transfer to humans?

Pinkeye caused by Moraxella is not zoonotic and therefore cannot be transmitted to people.

11. How resistant to antibiotics is pinkeye? If it is resistant, how did it build up its resistant?

In our clinical experience, we have not found isolates of Moraxella bovis or Moraxella bovoculi to necessarily be more resistant to antibiotics. Instead, we have found both Moraxella bovis and Moraxella bovoculi (often several strains) in severe ocular lesions that are not responding to antibiotic therapy. The bacteria seem to work synergistically to cause more severe ocular lesions. Recent research has determined no obvious detection of resistance.

12. Is there a current new strain of pinkeye that is more prevalent in herds in the Northeast area?

Moraxella bovis is still considered the primary bacteria causing pinkeye. But more recently, Moraxella bovoculi has been identified as a co-bacteria playing an important synergistic role in the pathology of the ocular lesions. Although commercial vaccines are available for both Moraxella bovis and Moraxella bovoculi, controlled studies have not demonstrated protection.There are many strains of Moraxella bovis and Moraxella bovoculi and the vaccines have likely failed to control pink eye on individual farms because they do not contain the strains occurring on the farm. There have been testimonials in farm journals of successes when producers have used autogenous vaccines made from strains of Moraxella bovis and Moraxella bovoculi cultured from eyes of their calves. Our clinical experience suggests an autogenous vaccine can be helpful on farms experiencing severe pink eye problems that are not responding to antibiotic therapy. Producers should involve their veterinarian if they are considering incorporating an autogenous vaccine for pinkeye in their program. Autogenous vaccines take a few months to make so they realistically are not helpful until the following season(LS20190727-AniSci-OhioBoyle)

Summer is often the time where cattle have an increase of risk for pinkeye due to a series of irritants like flies, dust, and sunlight. There are also different strains of pinkeye at make it very hard for some producers to combat.

Phto credit: Courtney Love

Special Sections Editor

Courtney Love is Special Sections Editor at Lancaster Farming. She can be reached at 717-721-4426 or


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