The Cow-Calf Manager
Livestock Update, June 2003
John B. Hall, Extension Animal Scientist, Beef, VA Tech
Warm spring and summer days will bring plentiful forage this year, but along with the benefits of summer come pinkeye. Pinkeye is a problem for producers because it lowers the value of feeder calves, and cows often have limited sight in affected eyes. Impact on the beef industry may be $150 million per year by some estimates. Research in Kentucky indicated that calves with pinkeye weighed 36 to 40 lbs less than their unaffected cohorts. In addition, pinkeye can be difficult to treat because cows and calves are often summered in remote pastures. Therefore, prevention is the key to minimizing the impact of pinkeye.
Pinkeye (keratoconjunctivitis) is an infection of the conjunctiva or connective tissue surrounding the eye and the cornea. It is caused by the moraxella bovis bacteria. This bacterium is harbored in the lachrymal (tear) ducts of infected cows. Cows serve as a reservoir of the bacteria even after the infection has healed on it own. Face flies are the vector that carries the bacteria from infected cattle to uninfected cattle.
Face flies feed on the lachrymal secretions of cattle as well as cell scrapings from the cornea of the eye. As the flies feed, they create small scratches on the surface of the eye. This creates a point of entry for any bacteria that they might be carrying in their mouth parts or salivary glands. If they are carrying the bovis bacteria then pinkeye can start.
Preventing pinkeye focuses on three main areas: 1) reducing eye irritation, 2) face fly control, and 3) nutrition. Another possible area is vaccination. A full pinkeye prevention program requires management of all three (or four) areas.
Eye irritation in beef cows and calves is a result of environmental factors. The principal eye irritant on Virginia beef operations is seed heads, grass stems, and weeds in pastures. Weedy or overgrown pastures forced cattle to push their heads deep into the forage to select the more desirable growth. Seed heads and stems can cause physical abrasion to the eye resulting in an opportunity for bacterial infection. Brush such as multiflora rose or hawthorns can also cause eye damage that may lead to pinkeye.
If pastures are mowed or clipped they should be clipped low enough so cut stems are 4 inches or less in height. Simply removing the seed heads and leaving the stems may increase eye irritation. A combination of proper grazing management and clipping of pastures or hay making will decrease cattle eye injuries.
Another source of eye irritation for cattle is dust. Most VA cow/calf operations are pasture based so dust is a minor problem. Principal areas that may need dust control are working facilities and areas around waterers. Working cattle in the early morning when humidity is high will help reduce dust. Weaning fall-born calves on grass rather than in the drylot will also reduce dust irritation of eyes of young cattle.
The key management strategy is good fly control. Fly tags are very effective for horn flies but less effective for face flies. In addition to fly tags, producers may want to use dust bags or face bullets. Bags and bullets can be located near salt feeders, but care should be taken not to accidentally contaminate the mineral source with the fly control product. Sprays are also an effective control method, but require more labor and frequent application. Because face flies are not blood sucking flies, they are not easily killed by systemic or pour-on type fly control products.
Most fly control products should first be applied in early June (East of the Blue Ridge) or mid to late June (West of the Blue Ridge). Fly control products should be rotated annually, and products in fly tags and dust-bags should be different. Care should be taken not to "double dose" animals with organophosphate-based fly control products. In general, if an organophosphate is used in a dust bag then pyrethrins or other non-organophosphate eartags should be used. Virginia Tech's former Extension veterinarians developed a detailed publication on external parasite control in beef cattle (ext. pub. 400- 802). To obtain this publication, see the VA Cooperative Extension website at http://www.ext.vt.edu or contact you local Extension office.
Nutrition is essential to the health of all cattle. Proper nutrition results in good immune function which is important to disease prevention. Good forage management will ensure cows and calves receive adequate energy and protein to maintain animal health as well as produce heavy weaning weights.
Trace minerals are the nutrient most likely to be deficient in cows and calves grazing spring and summer pastures. Specifically, selenium (Se) and copper (Cu) are very deficient in summer grazed pasture. Although these minerals will not prevent pinkeye, they are important minerals involved in immune function. Improved immune function will help cattle fight all infections including pinkeye.
Although several pinkeye vaccines are available, none of the vaccines provide complete protection against pinkeye. Producer satisfaction with vaccination programs is highly variable. Vaccination programs appear to be of most benefit in herds that have a high incidence of pinkeye. Producers should consult their veterinarian when considering a pinkeye vaccination program.
When cattle get pinkeye despite a prevention program, antibiotic treatment will be necessary. Systemic oxytetracycline or penicillin administered into the third eyelid are effective treatments. Dr. Dee Whittier, former Extension veterinarian, wrote an excellent article on treatment of pinkeye (see June 1998 Livestock Update). Producers should contact their veterinarian on current treatment recommendations.
However, a good prevention program is still more cost effective and considerably less labor than a treatment program.