Cow Tales
Winter Pinkeye
You will be hard pressed to find a fly in South Dakota this time of year. We have always been taught
flies cause pinkeye. So where does winter pinkeye come from? Obviously there must be more to the
story and there is. Pinkeye is a multifaceted disease that can leave producers scratching their heads
looking rather pensive. Time of year, vaccination, forage maturity, cattle oilers, fly sprays, fly tags, fly
predators, feeding practices, and treatment choices are just a few of the considerations that need to be
addressed.
Pinkeye is a lay term for infectious bovine keratoconjunctivitis. It is easy to see why people refer to the
condition as pinkeye. By definition it is inflammation of the cornea of the eye caused by an infectious
pathogen. The cornea is the clear portion of the eye that allows light into the eye and is surrounded by
the whitish colored sclera. The cornea is made of a network of protein fibers perfectly oriented to allow
light to pass through so it appears clear. The surface of the cornea is covered with a single layer of
specialized epithelial cells. According to the definition, pinkeye is inflammation of that specialized layer
of cells and often the protein fiber network that lies beneath,- a corneal ulcer. Some of the light is
reflected causing the cornea to look cloudy when the protein fiber orientation is disturbed by bacterial
enzymes, inflammatory mediators, and fluid.
Winter pinkeye is most often caused by management feeding decisions. Place a round bale in a pen and
cattle will bore a hole to the center. The outer six to eight inches of the bale is susceptible to rain and
rot while the inside is relatively free from the effects of weather. But, boring holes can be devastating to
eyes. Cattle abrade their corneas in their zest to reach the more nutritious center of the bale. Forage
related eye trauma also occurs in late summer as grasses grow taller and mature. The increased texture
enhances the ability of the forage to cause eye trauma while the cattle graze. The surface of the eye
harbors potentially pathogenic or troublesome bacteria that aggravate feed induced eye trauma.
Management practices that minimize round bale feeders will help to minimize winter pinkeye. We
recommend unrolling round bales or feeding ground hay.
Infectious causes of winter pinkeye include viruses and more often bacteria. The viruses are IBR or “red
nose” and rarely a lesser known virus called malignant catarrhal fever. With IBR the symptoms can be
mixed with pinkeye, respiratory issues, and even abortion. The most common pathogens associated
with pinkeye are bacteria. The traditional bacteria are called moraxella bovis although many other
species can play a lesser role. This is the type of bacteria that is in commercial pinkeye vaccines. These
bacteria have specialized protein structures called pili that adhere to the surface of the eye and start the
disease process. Commercial vaccines are designed against these pili so the bacteria cannot attach
themselves to the eye. The vaccines are pilus specific so bacteria with different pili are unaffected. The
specificity of the vaccine for a limited number of pilus types means the vaccine has a narrow range of
cross protection. This partly explains the variable success of a vaccine in different herds or a sudden
increase in pinkeye incidence in a well vaccinated herd. Furthermore, the disease process is enhanced
by irritants like ultraviolet light, dust, forage, etc. The bacteria are spread from one animal to another
by direct contact in tear and nasal secretions, flies, and other inanimate objects.
More recently an additional type of bacteria has been recognized as a significant contributor to pinkeye.
Moraxella bovoculi seems to be a stronger fighter, a pinkeye superpower that causes more severe
disease and is less responsive to medical treatment. There have been many recent name changes but
producers tend to call it sheep pinkeye stemming from a former name, moraxella ovis. It has proven to
be a significant contributor to winter pinkeye in many herds. This type of bacteria is not a component of
any commercial vaccines and no cross protection seems to exist from the moraxella bovis strains. But,
the producer can work with their veterinarian to culture this aggressive pathogen and have an
autogenous vaccine made for their herd.
Treatment is centered around some sort of antibiotic. Drops or ointments can be applied to the surface
of the eye. Topical antibiotics work well when administered three to four times a day for multiple days.
The frequent administration is necessary because the tear film on the surface of the eye is shallow and
can’t hold antibiotics for any measurable amount of time. The traditional veterinary approach was to
inject a small amount of antibiotic in the subconjunctival space. Sometimes the injection was combined
with a steroid to reduce inflammation. This practice is still debated amongst veterinarians. Some
studies indicate a reduction in healing times and would suggest no effect. For sure this technique
requires patience and adequate restraint. Newer treatment programs employ systemic antibiotics
administered in the neck in compliance with beef quality assurance guidelines. Additionally, it is always
a good idea to cover the eye with a semi-permanent patch. The patch blocks the sun relieving some
pain, reduces transmission by flies and inanimate objects, and minimizes ongoing trauma by physical
irritants.
Producers need to recognize the many aspects of pinkeye and especially the management
considerations of winter pinkeye breaks. Efforts should be focused on reducing the effects of flies.
Many products are available with varying success including oilers, sprays, pour-ons, and fly tags. Steps
should be taken to match application with peak fly season if possible. Minimize dusty environments and
manage forage availability to decrease the likelihood of mature forage playing a role. If the disease
seems to not fit any of the traditional causes or they are refractory to treatment, then the eyes need to
be cultured to rule out moraxella bovoculi. Treatment programs should be designed with the help of
your local veterinarian. The animal welfare and economic implications of pinkeye are too important to
ignore.
Nerd Word
Blepharospasm – spasm of the orbicularis oculi muscle of the eyelid. In other words, spastic blinking.
Blepharospasm is a typical pain response of corneal ulcers in bright light.
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