Pinkeye is a highly contagious infectious bacterial disease of the eye of cattle caused by Moraxella bovis (M. bovis).   Costs resulting from decreased weight gain, milk production, and treatment were estimated to be $150 million in the U.S. alone, according to a 1993 study.  Pinkeye (1.1% infection rate) was second to scours and as the most prevalent condition affecting 1996 born unweaned calves over 3 weeks old, according to the National Animal Health Monitoring System of the USDA: APHIS: Veterinary Services.  Pinkeye (1.3% infection rate) and Footrot (0.8% infection rate) were the two most prevalent conditions affecting all breeding beef females (replacement heifers and cows), according to the same 1997 report of 1996 conditions. 

Cause:   M. bovis is the primary infectious agent initiating Pinkeye.  Other microorganisms include Chlamydia, Mycoplasma, Acholeplasma or viruses such as the Infectious Bovine Rhinotracheitis (IBR) virus, can either add to the severity of the disease process or may serve as predisposing factors permitting a secondary infection with M. bovis. 
Other factors instrumental in causing eye irritation, thereby allowing for invasion of M. bovis and subsequent disease, are excessive ultraviolet light (sunlight), the face fly (Musca autumnalis), the house fly (Musca domestica), the stable fly (Stomoxys calcitrans), plant material and dust. 
 
Ultraviolet (UV) light is especially a problem for cattle lacking pigmentation around the eye.   Lack of pigmentation allows increased UV radiation to sensitize the eye resulting in inflammation and subsequent infection. 

Flies not only serve as irritants as they feed on secretions from the eye; they also serve as a means of transmitting M. bovis from infected to non-infected animals.  Face flies can remain infected with M. bovis up to 3 days following feeding on infected material.   Under experimental conditions, disease transmission is uncommon without the presence of face flies and is common with flies present. 

Cool and warm season grasses, hybrid Sudan grass and other forage sorghums, weeds and brush produce air-borne irritants, pollen and chaff, as well as serve as mechanical irritants.   When animals eat out the middle of round bales, leaving a hay shelf over their heads, the incidence of foreign body irritation is greatly increased.   The same situation occurs when hay is fed in overhead feeders.  This is especially true with wheat hay or hay containing cheat grass. 
 
Dust is more of a problem in confined feeding operations and is of minimal importance compared to UV radiation, flies and plant material. 

Treatment:   According to antimicrobial sensitivity studies, M. bovis is most often susceptible to oxytetracycline (LA-200^TM IM or SQ, Bio-Mycin 200^TM SQ, and AnchorOxy 200^TM SQ), ceftiofur (Naxcel^TM,for use by or on the order of a licensed veterinarian), penicillin, and sulfonamides.   It must be remembered these sensitivity patterns can and do change, making it necessary for your veterinarian to sample a representative number of infected cattle in your herd to determine proper drug usage.  (Note: IM=intramuscular; SQ=subcutaneous). 

Long-acting oxytetracycline has shown to be an effective treatment in calves when used early in the disease process.  Long-acting oxytetracycline has been shown to clear M. bovis from the infected eye within 24 hours of the first injection, thereby eliminating the treated animal as a source of infection for other non-infected animals.  Penicillin injected subconjunctivally (the thin membrane covering the white of the eye), has had similar healing rates as long-acting oxytetracycline injected intramuscularly but is more labor intensive.   A combination of intramuscular long-acting oxytetracycline followed by feeding 2-grams/head/day oxytetracycline in alfalfa pellets was reported effective in reducing the severity of a naturally occurring outbreak of Pinkeye in 6-month-old Hereford calves.  Also, calves receiving the oxytetracycline combination required fewer additional treatments than did calves treated with only subconjunctival procaine penicillin g.  Other microbial products are used topically in the eye, but due to excessive tearing, their effectiveness is short lived and requires repeated treatments. 

When severe corneal ulceration exists, protect the eye from UV light, flies and other irritants through the use of eye patches, suturing the eyelids or creating a 3rd eyelid flap.  Consult your veterinarian for assistance in these methods to enhance the healing process. 
 

• Follow all label instructions
• Administer all intramuscular (IM) injectables in the neck and all subcutaneous (SQ) injectables in the neck or behind the shoulder.
• Do not administer over 10 ml in one injection site.
• Recheck all withdrawal times with your veterinarian.
• A veterinarian - client - patient relationship is necessary for the use of all prescription drugs and drugs used off-label (at dosages and for purposes other than defined on the label).