Focus on Herd Health

By Jacques Van Zyl, DVM, Metzger Veterinary Services

Pinkeye in Cattle

Eye problems are common in cattle, particularly during the summer months. The most significant eye disease in cattle is called Infectious Bovine Keratoconjunctivitis (IBK), or more commonly known as pinkeye.

For the purpose of this article, when I am referring to pinkeye, I am referring to IBK, which is defined as a herd level disease affecting only the eyes. A large proportion of the herd may be affected, and the disease is characterized by rapid spread between animals with symptoms such as inflamed conjunctiva (conjunctivitis), runny eyes (epiphora), squinting (blepharitis), inflammation of the cornea (keratitis), cloudiness of the cornea (corneal opacity) and/or a physical defect of the cornea (ulceration).

Diseases that affect the eye often look alike. As a result, the term pinkeye is often incorrectly applied to many different ocular diseases in cattle. If you notice that your cattle have runny or sore eyes, this does not necessarily mean they have pinkeye. Other diseases that lead to runny or cloudy eyes include Infectious Bovine Rhinotracheitis (IBR), Malignant Catarrhal Fever (MCF) or Bovine Viral Diarrhea (BVD). These diseases have clinical signs that impact the entire body such as fever, diarrhea, or dull demeanours. Other, more mild infections of the eye can simply cause runny eyes or squinting. Care must be taken to correctly identify which disease is impacting your herd so that you can treat appropriately. The overlap of clinical signs that we see between ocular diseases plays into the difficulty of appropriately diagnosing pinkeye, and also in determining how prevalent this disease truly is.

Pinkeye is known to be caused by a bacteria called Moraxella bovis. It is important to note that there are many other bacteria that have also been associated with pinkeye infections in cattle. These include Moraxella bovoculi, Mycoplasma bovis, and Mycoplasma bovoculi. While none of these other bacteria have strong support as a direct cause of pinkeye, they may predispose animals to the infection and can even act in synergy with Moraxella bovis to worsen the disease.

Pinkeye usually starts as clear discharge from one or both eyes that can become purulent (yellow). As the infection progresses, the centre of the eye becomes cloudy as fluid leaks into the cornea. The cornea then turns to a yellow color and can develop a red rim before developing an ulcer or even rupturing. Luckily, cattle have a remarkable ability to repair their eyes. If we can initiate treatment, the eye can heal in one to three weeks, with the average herd outbreak lasting approximately 30 days.

Much like the bacteria that cause shipping fever in cattle, Moraxella bovis and Mycoplasma bovoculi can be found on the eyes of healthy cattle. Under normal conditions, the eye typically resists infection by washing away any bacteria with tears, which contain antibodies to fight infection. For infection to occur, there generally needs to be other predisposing factors. These can either be in the form of another infectious agent like the bacteria listed above, or they can be environmental factors. The more common environmental factors include, but are not limited to, face flies, UV light or damage from plants, pollens, or dust.

Face flies are commonly thought to be a leading contributor to pinkeye. As their name implies, they spend most of their time around the face as they feed on bodily fluids including tears. When they land on the eye, there is direct damage to the surface due to rasping of their teeth. Moraxella bovis live in the gut of these flies and they regurgitate the bacteria onto the eye. This allows the bacteria to get a good hold in damaged sections of the eye and can lead to infection. When cattle have a pinkeye infection, the flies tend to spend more time on affected eyes, which can contribute to the spread throughout the herd. Face flies are more active at temperatures between 25-29°C and fly populations generally peak between late June and early August in North America. This coincides with the period in which pinkeye tends to be the most prevalent.

Other environmental factors that impact susceptibility to the disease include UV light and mechanical irritation. UV light damages the cells that make up the outer layer of the eye. When damaged, these cells become what are known as ‘dark cells’. Moraxella bovis selectively attaches to these dark cells, so if an eye contains more dark cells, it is more likely the bacteria will be able to grab hold and cause an infection. Lastly, anything that causes direct damage to the eye will allow the bacteria to colonize and predispose to infection. This includes dust, pollens, and grass awns.

If you notice an outbreak of pinkeye in your cattle, treatment should be initiated immediately. Conditions that cause pinkeye in one animal are likely to be affecting others in the herd. Pinkeye is a painful condition in cattle, and treatment has been shown to improve healing times and reduce the risk of poor outcomes. When determining what to treat with, a major consideration should be which antibiotics are best able to reach the site of infection. In Canada, Oxytetracycline, Florfenicol and Tulathromycin are labelled for the treatment of pinkeye. Supplementary care such as antiinflammatories may also be warranted. Some producers opt to cover the eye with a patch to keep flies and debris out during the healing stage, and some veterinarians have even stitched the eye closed for the same reason. Many times, these outbreaks occur when cattle are on pasture and individual treatment of animals is unfeasible. Consult with your veterinarian as to which antibiotic is most appropriate, and to determine if there are other formulation options available to suit your needs.

Prevention should be focused on minimizing the contributing factors. As previously mentioned, Moraxella bovis can be found on healthy eyes, so eliminating the bacteria itself from cattle is unfeasible. Efforts are typically directed towards fly control as the amount of pinkeye in a herd has been observed to decrease after fly control products are applied. Pyrethroid insecticides are generally used, and there does not seem to be a difference in efficacy between ear tag or pour-on formulations. Nonchemical measures such as harrowing fields to break up cow patties or appropriate rotations can also be implemented to reduce fly numbers and help prolong the usefulness of chemical products. Providing shaded areas to decrease UV light and mowing pastures before the grass is headed out can also decrease mechanical irritation to the eye.

Vaccination has also been looked at for prevention of pinkeye. There are a few injectable vaccines on the market, but evidence that they protect against pinkeye is variable. Autogenous vaccines are specifically made from bacterial strains isolated from affected animals and intended to be used in the herd where the diseased animal originated. These vaccines are made in licensed facilities and intended to be used when a commercial product is unavailable or not effective. Consistent and reliable information on the efficacy of autogenous vaccines is lacking. Currently there are no intranasal or aerosolized vaccines on the market.

Pinkeye outbreaks can be frustrating for producers due to the difficulty of accessing cattle on pasture. Care must be taken to ensure appropriate diagnosis so treatment can be initiated. If you are experiencing pinkeye in your cattle, talk to your veterinarian to discuss treatment options. This may also be a great time to discuss preventative measures for future years.