Pink eye is one of the most common conditions affecting cows and calves on pasture and causes significant losses for the cattle industry. The national Animal Health Monitoring System (U. S.) reports that pink eye is second to scours and diarrhea as the most prevalent condition affecting unweaned calves over three weeks old. Pink eye alone has been estimated to reduce weaning weights in calves as much as 60 pounds. Add to this the sale ring discounts for bad eyes that often exceed $10 per cwt and the total bill for every calf affected with pink eye reaches $100, or more. The production effects include:
Intense discomfort, pain and temporary or permanent blindness reduces gains.
When treated early, differences in weaning weight between infected and healthy calves is markedly reduced. While pink eye predominantly infects only one eye, infection of both eyes can occur, increasing losses up to threefold.
Post-weaning, animals suffering from pink eye, have lower ADG, weight per day of age, 365-day weight and final weight.
Increased mustering costs due to blind or partially blind animals.
Increased mortality due to thirst, starvation or injury on pasture.
Milk production is reduced in affected cows and the susceptibility to cancer eye is increased.
There are occupational health and safety concerns in feedlots when handling calves that are partially blind.
Pink eye, known as infectious bovine keratoconjunctivitis (IBK), is a contagious bacterial infection caused by organisms like Moraxella bovis that infect the surface of the eye and the conjunctiva or tissues surrounding the eye. The number of organisms proven or implicated to cause IBK in cattle has expanded over the years and the names of bacteria have changed.
Two microbial factors are important for the development of IBK. The first, are surface proteins that allow Moraxella to adhere to the cornea. The second are toxins that appear to “punch” holes in the surface of the cornea.
While bacterial organisms like Moraxella bovis are the root cause of pink eye, the primary vector responsible for spreading the bacteria from animal to animal is the face fly as it feeds on tears produced by infected and irritated eyes. Face flies visit several animals every day and rapidly spread pink eye bacteria throughout a herd. Face flies can remain infected with M. bovis up to three days following feeding on infected material.
Other environmental factors like awns, dust, pollen and UV light increase trauma to the eye, facilitating establishment of infections. Fly control and management of environmental irritants become key components in pink eye prevention. The effect of ultraviolet light is especially a problem for cattle lacking pigmentation around the eye. Dust can be a problem in confined feeding operations.
Calves are more likely to develop the disease than adult cattle, as adult cattle appear to develop protective antibodies on the surface of the eye. For some reason, bull calves have a higher incidence of disease than heifer calves. Carrier cows that maintain infection from year to year probably occur.
Clinical diagnosis is based on the appearance of a central corneal ulcer, corneal clouding and conjunctivitis.
Antimicrobial therapy is often indicated and will be the basis of outbreak management along with elimination of any predisposing factors. Producers should consult a veterinarian when considering treatment and control options. The choice of antimicrobials includes a number of the broad-spectrum products like long-acting oxytetracycline, florfenicol, ceftiofur and tulathromycin. Products not specifically labelled for IBK, require a veterinary prescription and veterinary instruction on extra-label use. In addition to injectable antimicrobials, procaine penicillin G (300 IU) administered beneath the conjunctiva of infected eyes, with or without a corticosteroid like dexamethasone, generally provides prompt relief. Severe cases may call for the application of an eye patch or temporary closure of the eyelids by suturing.
There are a number of commercial IBK vaccines on the market. Some require two doses for immunization, others require just one. The primary problem with vaccination is that producers do not vaccinate soon enough in the year for susceptible cattle to develop immunity prior to the onset of the IBK “season.” This is an important part of prevention, one often neglected until outbreaks occur.
Since IBK is frequently more severe in calves, it is important they become the focus of preventive measures. Face fly control is a very important factor in preventing IBK. While use of insecticide ear tags can be an effective part of prevention, insecticide resistance plays a role in the choice of appropriate tags. Food animal practitioners can certainly provide valuable advice to producers regarding face fly control strategies. Sprays, back rubbers, face rubbers, and dust bags can help reduce the fly populations early in the season, before ear tag application. Compounds fed or given orally to kill fly larvae in manure can be very effective.
From a biosecurity perspective, the use of disposable latex gloves is recommended when examining eyes. The IBK agents will bind to hands and are effectively transmitted from animal to animal. Because clothing is easily contaminated, leave pink eye treatments until after routine animal-handling procedures on healthy animals are done. Change clothes after handling pink eye cattle and before handling normal cattle. Producers should routinely disinfect equipment used on animals with IBK. Things like forceps, hemostats, or tweezers used to remove foxtails, nose tongs used for restraint, and rope or nylon halters should be disinfected. It is also a good idea to clean and disinfect the head catch or head restraint area of the chute.