As warmer weather hits, it’s time to brush-up on the latest information about pinkeye in cattle. According to the University of California Davis School of Veterinary medicine, pinkeye is the most common infectious eye disease in cattle. The root of the disease usually starts with Moraxella bovis bacteria. It can cause painful corneal ulcers and inflammation of the eye and skin surfaces around the eye. This can lead to corneal infections which can result in scars or even eyeball ruptures. Left untreated, it can cause permanent blindness.
Pinkeye infections can happen throughout the year, but occur most often in the summer months. Increased exposure to sunlight and dry or dusty conditions can be contributing factors to pinkeye infections. Plants like foxtails or tall grass can get caught or scratch the eye when cattle bend down to graze. This can damage the cornea and has the potential to lead to infection. Farmers can also spread the disease by not wearing disposable gloves or not using disinfectants after treating affected animals.
But the main way that pinkeye is spread through a cattle herd is by flies. Moist conditions usually make fly populations worse.
Flies also increase the chances of exposure and spread of M. bovis bacteria by feeding around the face and eyes of affected cattle and then transferring infected eye fluids to other animals.
So, how do you recognize pinkeye? Below, 7 things to look for from Professor John Angelos of the University of California Davis. He has spent more than 15 years researching causes and potential treatments for pinkeye in cattle.
Common Signs:
- Excessive tearing
- Frequent blinking or squinting
- Decreased appetite due to eye pain
- Corneal ulceration and cloudiness
- Potential blindness or eye rupture
- Can affect one or both eyes
- Younger cattle typically more susceptible
Read more at vetmed.ucdavis.edu
Janna Kincheloe and Russ Daly of iGrow.org, a division of the SDSU Extension, provide a detailed description on how to recognize pinkeye:
Within the first three to five days after infection, cattle blink frequently and have excessive tearing, in addition to redness in the conjunctiva (white part) of the eye. Cattle in this beginning stage will often seek shade, typically decreasing the time they spend grazing. Pain may also contribute to reduced feed intake. After a day or two, these signs progress to a small ulcer in the center of the cornea which appears as a small white spot. The cornea develops a cloudy blue-grey appearance due to inflammation. One or both eyes may be affected, and the eye(s) are often held shut due to pain.
Later stages of pinkeye infections cause eyes to become more cloudy and pink as the disease spreads to the inner parts of the eye.
If left untreated in the early stage of the disease, the ulcer will continue to spread across the cornea, and the eye will become increasingly cloudy. Blood vessels from the outside of the cornea begin to grow to help with healing, which gives the cornea the classical pink appearance. The ulcer will eventually cover most of the cornea and the inflammation will spread to the inner parts of the eye. If this occurs, the inside of the eye fills with a pus-like substance called fibrin that gives the eye a yellow appearance. Rupture of the eyeball is rare but may occur with a severe infection.
The University of Illinois Extension published an article by several Virginia Tech veterinarians (W. Dee Whittier D.V.M., Extension Specialist, John Currin D.V.M., Nancy Currin D.V.M., Large Animal Clinical Sciences) that describes pinkeye as having four stages. 
Stage 1: Cattle have excessive tearing and increased sensitivity to light. They will blink frequently and there is redness along the eyelids. Cattle will often seek shade, which will decrease their grazing time. Pain associated with pinkeye also decreases their feed intake. Stage I will progress to a small ulcer in the center of the cornea which appears as a small white spot. The cornea develops a slightly cloudy grey appearance due to inflammation. One or both eyes may be affected.
Stage 2: The clinical signs described in Stage I continue, but the ulcer spreads across the cornea. As more inflammation occurs, the cornea becomes increasingly cloudy. At this point, some of the dark color of the iris can still be seen. Blood vessels from the outside portion of the cornea begin to grow across the cornea to help with healing. These blood vessels make the cornea appear pink, which is how the disease received its name.
Stage 3: The ulcer covers most of the cornea and the inflammation continues to spread into the inner parts of the eye. When this occurs, the inside of the eye fills with fibrin, which is a pus-like substance that gives the eye a yellow appearance versus the typical brown appearance.
Stage 4: The ulcer extends completely through the cornea, and the iris may protrude through the ulcer. The iris will become stuck in the cornea even after healing. This may lead to glaucoma or persistent swelling of the eye. This eye will be partially or completely blind. The eye may go on to completely rupture, and will develop a shrunken appearance or enlarge if glaucoma (increased eye pressure) is present. This eye will be permanently blind.
Read more at web.extension.illinois.edu
It’s best to try and prevent pinkeye before it starts, and prevention treatments should be continuous. Right now, the best ways to prevent it include managing the flies, vaccination, and simple good hygiene practices.
Fly control: Controlling flies should help to reduce the risks of disease spread between animals in a herd. Traditional methods have included the use of insecticide-containing ear tags, dust bags, and systemically- or topically-applied parasiticides.
Fly control treatments abound. Lee Townsend, Extension Entomologist at the University of Kentucky, wrote an article with his latest recommendations called “Insect Control for Cattle-2018,” click the link to read it. We also wrote a more in-depth article about feed-through fly control recently. Read it here.
If the fly population around your herd has been controlled, the another step in preventing pinkeye infections is to vaccinate.
Promote optimal health and immunity & vaccinate before there’s a problem: According to Dr. Angelos, vaccination is the main crux of prevention, although producers can still experience variable results with today’s vaccines. When vaccinating animals, it is important to vaccinate well in advance (ideally at least four weeks) of the anticipated summer onset of pinkeye in your herd, so that cattle will have enough time to mount an effective immune response following vaccination. Because young animals tend to be most affected, it is critical that young stocks are part of the vaccination program. Finally, it is important to make sure that cattle have adequate levels of trace minerals such as copper and selenium for a properly functioning immune system. Dr. Angelos and his team continue to do research at UCD SVM to develop better pinkeye vaccines that will be more effective than currently-available vaccines.
Read more at vetmed.ucdavis.edu
Kincheloe and Daly argue that vaccines are helpful, but don’t always offer complete coverage, as there are more than 20 different strains of M. bovis bacteria. Vaccines can also exacerbate symptoms if given during an outbreak. Vaccines can be formulated to specifically address the strains of bacteria causing pinkeye in your herd, but this is really only practical for large herds, and research about its effectiveness is fairly new.
Autogenous pinkeye vaccines, as well as over-the-counter vaccines, have not uniformly resulted in complete protection from the disease, but may be useful in certain situations.
Pinkeye infections are incredibly common, which makes good hygiene practices incredibly important. Dr Angelos of UC Davis suggests some basic practices:
Practice good sanitation/hygiene: To avoid inadvertently spreading infective bacteria between animals, use of disposable gloves is recommended when handling pinkeye-affected cattle. These gloves should be changed or at least disinfected between animals. In addition, consider changing clothes or disinfecting plastic aprons and halters between cattle. One commonly used disinfectant is 10% household bleach made by mixing one part of regular strength household bleach to nine parts water (or ~1-1.5 cups regular strength bleach per gallon of clean water). If using concentrated bleach you will only need ~1/2 cup per gallon of clean water. This mixture should be made fresh daily to maintain effectiveness. Also, bleach becomes less effective when it becomes heavily soiled with dirt or manure and other organic material. For that reason it may need to be refreshed more frequently, depending on use and working conditions.
Read more at vetmed.ucdavis.edu
Virtually all farmers raising cattle will experience an outbreak of pinkeye at one time or another. Staying ahead and trying to prevent outbreaks are critical. Practice basic good hygiene, vaccinate, and treat for flies to keep pinkeye infections at a minimum. When outbreaks do occur, be able to identify early pinkeye symptoms so you can minimize the likelihood of permanent damage to the eyes.
This is Part I of our three-part series covering pinkeye in cattle.
What are the best pinkeye treatment options? Read part 2 of our series, “Pinkeye Treatment Options for Cattle“.
Learn how much pinkeye is costing you in part 3 of our series, “The Many Costs of Pinkeye“.
Images courtesy of Beef Magazine and Totally Vets
