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Oklahoma State University

Don’t let flies get the best of your cattle’s eyes

Tuesday, June 11, 2019

A case of healed pinkeye with a scar. Notice the central white spot, without any tearing or squinting. This is a case of pinkeye that has healed and left a scar on the cornea and no further treatment is required.

Spring rains ensured a bloom of various parasites, including flies. Significant growth and production losses can occur in cattle from the annoyance of flies – cattle spend time swishing tails, flipping heads and twitching skin, using energy and taking away valuable grazing time. Studies have shown 10 to 20 pound weaning weight advantages in calves when horn flies were controlled in cows. In addition to the irritation factor, flies can transmit an important bacterial infection that can escalate production losses and negatively impact animal welfare—pinkeye.

Pinkeye is caused primarily by the bacteria Moraxella bovis and can be carried between cattle on things like dust particles and the feet of flies. The bacteria are deposited on the clear surface of the eye – the cornea – and have the ability to grab on to ensure they can set up shop. The infection spreads to deeper layers of the cornea and causes a tremendous amount of pain and inflammation. If the infection advances to the point where it invades completely through the cornea, the eye can rupture. Lesser infections may result in permanent damage to the cornea reducing vision permanently.

The first signs of pinkeye are excessive tearing (you will notice wetness to the face on the affected side) and squinting. The squinting is a result of pain, which is made worse when animals are in bright sunlight. A white spot will begin to form in the center of the cornea signifying the beginning of damage to the eye. As the infection progresses, the whiteness spreads. Also the inner portions of the eyelids or the whites of the eyes may become reddened.  

As with all infections, early treatment yields the greatest successes. At the first sign of squinting and tearing, bring cattle to the chute and examine the eyes. It is important to first make sure that a foreign object, like a grass awn, is not causing the irritation. A central whiteness to the cornea is highly suggestive of pinkeye infection. Contact your veterinarian for his or her treatment recommendations. Several treatment options are available and are typically used alone or in combination, based on the severity of each individual case.

The first principle of pinkeye treatment is protect the eye. The goal is to prevent rupture and reduce pain. Eye patches and other devices may be used to cover the eye to keep out dust, flies, and sunlight. Some veterinarians advocate for suturing the third eyelid over the eye or the upper and lower eyelids closed to protect the cornea temporarily.

Next, address the infection. This can be done topically directly to the eye or through injection of an antibiotic, relying on the body to deliver the drug to the eye to treat the infection. Specialized techniques for keeping topical antibiotics on the eye, while limiting the need to apply multiple doses, exist. Antibiotics labeled for the treatment of pinkeye in cattle include the over-the-counter medication oxytetracycline (available as LA-200® or several generics) and the prescription antibiotic Draxxin®. Visit with your veterinarian about which of these products he or she prefers to treat pinkeye and be sure to follow the label directions exactly.

Finally, your veterinarian may recommend a pain relieving drug. While it is important to be careful when extrapolating pain criteria between humans and animals, we can be confident that corneal damage is painful based on their behavior. The cornea has lots of nerve endings and is very sensitive. 

In addition to looking at eyes to catch cases early, you can reduce the risk of infection. Take measures to control dust and grass height, which can both scratch the eye and transmit the bacteria. These are difficult to do and require some grazing planning. Fly control is a major consideration – both for pinkeye and for the irritation discussed earlier. Fly tags, topical pour-on products, pasture rubbing devices, fly-control mineral, and other products may be considered based on your operation’s management scheme. Finally, there are commercial vaccines available against the bacteria that cause pinkeye.

There are widely varying opinions among veterinarians and producers about the value of pinkeye vaccine and the research can be interpreted in many ways. A few things we know for sure: for the vaccines to be of any use, they have to be used very strategically, timed just right, dosed exactly as described on the label and cannot be relied upon to provide total control in the absence of other management control factors like fly control. At different points during fly season, recommendations for fly and pinkeye control change in order to maximize the effectiveness and value of the intervention.

As prey animals, cattle rely heavily on their vision for protection. Further, the pain and damage associated with pinkeye and flies are associated with great cost to animal welfare and to your bottom line. Communicate with your veterinarian about summer cattle issues to ensure cattle enter the fall in tip-top shape.

MEDIA CONTACT: Derinda Blakeney, APR | OSU Center for Veterinary Health Sciences | 405-744-6740 | derinda@okstate.edu

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