Pinkeye is often thought of as a seasonal disease, but can occur at any time of year. Production losses and treatment costs add up. Therefore, it is important for producers to recognize the causes of pinkeye. In general, any insult that causes irritation to the surface of the eye may be implicated in allowing bacteria access. For example, sunlight is thought to irritate and weaken the cornea. Furthermore, dust and tall seed heads cause irritation. Face flies scratch corneal surfaces and do the most damage by spreading the bacteria. In the winter, cattle spread the organism through contact at feeders and may scratch corneal surfaces on round bales.
There are two important bacterial organisms that cause pinkeye: Moraxella bovis and Moraxella bovoculi. Both may be transient organisms in the upper respiratory tract of cattle without any signs of disease. Recent research suggests that a majority of pinkeye outbreaks are mixed infections. M. bovoculi tends to be the most commonly cultured strain in the winter. It also tends to be the most resistant strain to antibiotic treatment, as approximately 40% of this strain does not respond to tetracycline antibiotics. Vaccination has been one tool that producers have utilized for prevention, but M. bovis has been the only strain available in a commercial vaccine. Therefore, outbreaks have still occurred in vaccinated herds due to M. bovoculi. Some vaccine companies are currently working towards licensing that will allow them to make a commercial vaccine for both strains. In the meantime, autogenous vaccines can be made from cultured eyes to offer more complete coverage. It is important to recognize that vaccination is just one tool in pinkeye prevention and that it does not eliminate the need for a good fly control program and pasture management.
Currently, there are only two classes of antibiotics labeled for treatment of pinkeye. Tetracycline is the most affordable option in the face of an outbreak, but residual cases may require re-treatment due to resistance. Sometimes other antibiotics are necessary when labeled use is exhausted. Timing and severity may require subconjunctival injections performed by a veterinarian. The third eyelid closure acts as a band-aid and supplies nutrients to the disrupted cornea, while shielding it from sunlight and other irritants. Typically, the stitch opens on its own in 2-3 weeks. Severely ulcerated eyes can be healed to minimize scarring and regain vision in many circumstances.
Ask us about vaccination and fly control options available and please give us a call in the face of an outbreak.