Pinkeye in cattle is a common disease that ranchers deal with this time of year when cattle are on pasture.
Pinkeye was described in cattle in North America back in the early 1800s and although there has been significant research into the disease, it still presents many unknowns and challenges.
Dr. Annette O’Connor, a faculty member and veterinary epidemiologist at the veterinary school at Iowa State University, presented her insights and research on pinkeye in cattle at a meeting of the Academy of Veterinary Consultants in Oklahoma City in April.
O’Connor described three kinds of herds with respect to pinkeye infections: herds that never get pinkeye, herds that sporadically get pinkeye infections and herds that consistently have pinkeye infections.
Unfortunately, we don’t have a good handle on why these problem herds occur and what factors are most important in creating the problems.
One of the herds at Iowa State University fell into the third category. It consistently had at least a third of the herd affected with pinkeye problems each year.
O’Connor described the significant production impact of the disease by showing that calves affected with pinkeye weighed on average 30 pounds less than calves not affected.
Calves with both eyes affected had even more dramatic decreases in productivity. Their weaning weights were 40 lb. less than calves not affected with pinkeye.
Post-weaning data was available on many of the calves and although there were some compensatory gains, calves affected by pinkeye before weaning still weighed on average 15 lb. less at 12 months of age.
The economic damage continues because calves weaned with obvious pinkeye scars are often discounted at sale time.
One of the more dramatic aspects of O’Connor’s research was her description of how rapidly the disease progressed in some of the experimental infections she followed.
Within five hours of experimentally infecting an eye, a one centimetre wide ulcer was already visible. Very dramatic lesions could be created within 24 hours.
O’Connor described how as a veterinary clinician she had initially been skeptical when producers had told her the cattle were fine yesterday and had dramatic lesions the next day.
After observing the rapid development of ulcers in the experimental infections, we now have a better understanding of just how rapidly these eyes can deteriorate.
Moraxella bovis is the name of the bacteria that is traditionally thought of as the primary cause of pinkeye infections.
This bacteria can persist in the nasal cavity and may be transmitted by face flies from one animal to another.
Recently, several other studies have suggested a number of other bacteria such as Mycoplasma bovis or Moraxella bovoculi could potentially be alternative causes of pinkeye outbreaks as well.
O’Connor’s research demonstrated that some of these bacteria were common in the eyes of cattle regardless of whether they had signs of pinkeye or not.
In addition, experimental infections with these bacteria did not consistently cause pinkeye lesions. She did not think these other species of bacteria played an important role in causing pinkeye outbreaks.
The traditional theory of some irritation to the eye along with Moraxella bovis infection is still the most likely two factors in causing pinkeye outbreaks.
The three main sources of irritation for pastured cattle are flies, UV light, and grass. Dust may also be a contributor in some cases.
UV light may be an important irritant especially in cattle with little pigmentation around the eye. Long grass can mechanically irritate the eye as well.
Preventing pinkeye is not always an easy task. Fly control through the use of a combination of ear tags, pour-ons, or insecticides can be one component of control, although resistance to insecticides can be an issue.
Pasture clipping can decrease irritation from pollen and seeds, but unfortunately, this is not always a practical solution.
Vaccines are available for pinkeye but these are not always effective perhaps due to the presence of multiple strains of the Moraxella bovis bacteria.
A veterinarian can recommend an appropriate treatment protocol for dealing with pinkeye cases when they occur.
Mild cases usually respond to systemic antibiotics such as long acting oxytetracycline.
More severely affected animals may require other therapies and in some cases the bacteria may be resistant to normal antibiotic therapy.