Bovine Eye Diseases: Pinkeye
Page Dinsmore, DVM, ILM-CSU
The summer requires renewed attention to cattle eye health. The two most common
problems-pinkeye and cancer eye-are responsible for serious losses due to:
1. reduced feed consumption from pain and blindness
2. treatment costs and milk discard from antibiotic use
3. reduced value at culling
This is the first of a two part article describing these two common conditions. Cancer eye
will be discussed in the next issue. Pinkeye (Infectious Bovine Keratoconjunctivitis) is a
contagious disease that damages the cornea (the clear portion of the eye) and conjunctiva.
The causative agent is Moraxella bovis, but other factors such as direct sunlight and dust
certainly contribute. Flies are important vectors involved in spread of the organism from
one cow to another. The immune status of the cow also appears to play an important role
in the disease occurrence. Cows are almost never affected with pinkeye more than once
in their lifetimes, and seldom are affected in more than one eye.
The progression of clinical signs of pinkeye is consistent and predictable. Excessive
tearing, reddening of the conjunctiva, and frequent blinking (lacrimation, conjunctivitis,
and blepharospasm) are followed within 1-2 days by corneal ulceration and cloudiness
(edema). The ulcer begins in the center of the cornea and may expand to occupy most of
the cornea. In severe cases the ulcer may erode the entire thickness of the cornea,
resulting in rupture of the eye and permanent blindness. Corneal edema may quickly
affect the entire cornea, resulting in the characteristic "blue eye" seen in advanced cases.
The eye is blind and very painful and the animal will hold it shut and avoid the sun.
Pinkeye typically occurs in an outbreak, affecting first lactation cows soon after calving.
Younger and older animals are affected less often. Due in part to differences in risk
factors and the presence of herd immunity, outbreaks occur at intervals of 3 to 5 years
with sporadic isolated cases appearing between outbreaks.The goals of pinkeye treatment
are to eliminate the causative agent using antibiotics and to prevent rupture of the eye.
Moraxella bovis is susceptible to most antibiotics including penicillin and
oxytetracycline. Early cases (tearing and conjuctivitis without ulcer and edema) are
successfully treated with topical antibiotics. We recommend that during an outbreak, first
lactation cows be examined daily and at the first sign of tearing, 1-2 cc of penicillin be
squirted in the affected eye for 2-3 days. Feedbunk lockups simplify this procedure. Such
early topical treatment will usually prevent progression to ulceration. Eyes with corneal
ulcers require aggressive antibiotic treatment and veterinary consultation. We use
subconjunctival injections of 1 cc of penicillin to achieve high levels of antibiotics in the
eye. Neither of these uses of penicillin (topical or subconjunctival) will result in violative
residues of antibiotics in the milk or meat. In beef cattle, a single dose of long-acting
oxytetracycline has been used successfully in early cases. This treatment is now approved
in dairy cattle, but witholding milk is necessary.
If the corneal ulcer is deep and appears likely to rupture, we sew the eyelids shut or sew
the third eyelid to the upper lid across the ulcer. These procedures should be performed
by a veterinarian."Pinkeye patches",although popular and easy to apply, only protect the
eye from the sun. Eyes covered with a patch cannot be medicated or monitored.
Corneal ulcer healing progresses in stages. Once the organism is eliminated, epithelium
quickly covers the ulcer and the eye is much less painful. The eye will cease its excessive
tearing and blinking and the animal will appear much more comfortable. Even though the
"blue-eye" (edema) and blindness may remain for 1-2 weeks after the ulcer is healed, the
eye no longer requires antibiotic treatment. Clearing of the edema begins at the edge of
the cornea and sight will return accordingly. A central scar at the site of the ulcer will
gradually shrink over a period of several weeks, but a small opaque area may remain for
the lifetime of the animal.
Prevention of pinkeye is limited to fly control, since little can be done to reduce dust or
exposure to sunlight. Several vaccines are available, most of which stimulate significant
levels of circulating antibody against the organism or its pili. (The pili facilitate
attachment to the conjunctiva.) There are numerous anecdotes in which producers
describe the worst outbreak of pinkeye ever seen in their herd; begin to vaccinate the herd
the following winter; and no pinkeye is seen that summer. However, controlled trials
have failed to show that vaccination will reduce the incidence of naturally occurring
pinkeye. The apparent benefits of the vaccine seen the year after pinkeye outbreaks are
almost certainly due to herd immunity stimulated not by the vaccine but by the outbreak
itself.