The bacterium Moraxella bovis is the most common cause of pinkeye. However, other Moraxella species and some viruses also can contribute to pinkeye. Outbreaks among cattle, including heifers, peak in the summer because of increased exposure to ultraviolet light.
Ultraviolet (UV) light from the sun is the primary trigger for pinkeye in cattle, says Lisle George, veterinarian and professor emeritus at the University of California – Davis.
Clinical research has found that shining UV light into the eye, and then infecting the eye with the bacterium M. bovis, enhanced the amount of pinkeye lesions and the severity of those lesions compared to pinkeye initiated by the bacterium alone, George explains. “UV light is the most important trigger.”
Summertime also is peak fly season, and flies are an important vector for the spread of pinkeye in the herd.
Aggressive monitoring for pinkeye, early intervention and preventative measures can dramatically reduce the number of animals that experience clinical disease signs.
Monitor heifers for early signs
After the M. bovis bacterium invades the eye, it secretes a protein toxin. This toxin kills the cells in the eye, George explains. Symptoms of pinkeye quickly ensue.
Catching symptoms early is key to a more efficient recovery. Early symptoms include squinting and excessive tearing. A trail of this discharge can be seen running from the eye down the side of the face.
Don’t wait for advanced symptoms to occur – the eye takes on a “pink” or cloudy, white appearance – before you take action.
“If you treat the very early cases, then you limit scarring in the eye, and you reduce the time it takes for them to heal,” George says.
Best treatment options
The Dairy Calf and Heifer Association’s Gold Standards II urges heifer growers nationwide to keep target treatment rates (from causes other than pneumonia) under 4 percent for heifers between six and 12 months old and less than 2 percent for heifers 12 months old to freshening.
These target treatment rates apply to pinkeye, as well as a number of other non-respiratory conditions and diseases.
If you spot pinkeye in the herd, take action to prevent it from further damaging the eye and spreading to other animals. The most effective approach is to treat individual animals systemically with a long-acting form of oxytetracycline, George says.
Most cases can be treated effectively with one or two doses of a commercial product labeled for the treatment of pinkeye.
Central Minnesota heifer grower Roger Imdieke has used a commercially available, injectable oxytetracycline with good results. The product he uses is FDA-approved for the treatment of pinkeye caused by M. bovis. Imdieke administers it subcutaneously to minimize injection-site blemishes.
Other therapies can be used, but you should consult with your veterinarian before implementing them. Prescription drugs not labeled for the treatment of pinkeye represent extra-label use, which requires a valid veterinarian-client-patient relationship.
During treatment, isolate infected animals. If that is not possible, ask your veterinarian about group feeding an oral oxytetracycline, George says.
When using any antibiotic, pay attention to milk withholding and meat withdrawal times.
Imdieke would much rather prevent pinkeye than go through the hassle and time commitment of sorting off heifers for treatment.
“It’s a lot easier to vaccinate (especially when you have some cattle on pasture) than it is to try and round up (heifers for treatment),” he says.
Although Imdieke has seen good results with vaccination, vaccines for pinkeye can yield mixed results. If you decide to use a vaccine, work with your veterinarian to establish a vaccination program best suited to the conditions and diseases on your operation.
Pinkeye is one of many diseases to consider addressing with vaccination, according to advice from the Gold Standards II.
Watch your timing when you administer pinkeye vaccines.
“Vaccinate before the onset of pinkeye season, which, in California, is usually about mid-April,” George says.
In Minnesota, the onset of pinkeye season starts later – in late May or June, so Imdieke holds off on vaccination until mid-May.
Imdieke raises heifers at two different locations. At one site, heifers have access to pasture, so he is vigilant about fly control to prevent the spread of pinkeye.
“The flies that I have over there are not (the same) flies that I have at the (other) farm site,” Imdieke says. “Because of the fly issue, I work hard at preventing (pinkeye) over there.”
Insecticide pour-ons, sprays and ear tags are effective ways to control flies around the face of cattle and prevent the spread of pinkeye from one animal to another. Fly traps, as well as back or head rubbers with insecticides, also are good fly control measures.
Imdieke uses a pour-on product for fly control.
The influence of irritants like long grasses and weeds, as well as air-borne irritants like plant pollen and dust, are “overblown,” George says.
If you want to clip pasture grasses to decrease irritation, that’s OK. However, because UV light is such a huge contributor to pinkeye infections, you may be further ahead to give cattle adequate shade so they can avoid excessive sunlight.
Early diagnosis, prompt treatment and preventive practices all help to reduce the damaging effects that pinkeye has on heifer growth and well-being. Take steps to control pinkeye this season. PD
The Dairy Calf and Heifer Association’s Gold Standards I and II outline production and performance expectations in six categories for Holstein calves from birth to six months old and for Holstein heifers from 6 months old to freshening. DCHA is the only national association dedicated to serving the dairy calf and heifer industry.
DCHA strives to provide information, education and access to leading research and technology to help its members be more profitable. DCHA members have the opportunity to network with producers, industry leaders and top academia to learn more about current issues affecting the dairy calf and heifer business. For more information about DCHA and the Gold Standards, visit www.calfandheifer.org or call 877-HEIFERS.