The tell-tale sign of a white spot on the eye immediately leads to concern and hopefully, quick treatment. But why wait until the onset of pinkeye, instead of taking measures to nip it in the bud before it hits?
Although pinkeye in cattle is a concern year-round, the summer months in particular can lead to a higher incidence of the infectious disease.
Pinkeye is a highly contagious disease and rarely affects just one animal in the herd. Though it is non-fatal, economic impact can be severe, with more than $150 million in losses per year in the U.S. alone, according to the University of Tennessee Extension.
Onset of pinkeye
The cause of the disease is usually the result of the bacterial organism M. bovisinfecting the surface of the eye. The bacteria attaches to the cornea and colonizes, creating inflammation in the tissue of the eyelid and eye. If the inflammation becomes severe enough, cornea ulcers may rupture and cause blindness.
The eye has a natural defense mechanism to the bacteria, so in order for it to invade, there must be an underlying irritation. Environmental factors such as sunlight, seed heads, and dust scratch the cornea of the eye, allowing the M. bovisbacteria to infect. Summer months have an increased level of these irritants, which is why there can be greater incidence of pinkeye.
In addition, the irritants increase tear secretions from the eye, which attract face flies that can quickly spread M. bovis. The bacteria lives in the eyes and nasal cavities of infected cattle and can be harbored for longer than a year in some carriers without causing symptoms.
Younger cattle are more susceptible to the disease, as mature animals likely have developed eye surface immunity as a result of prior exposure.
Transmission of pinkeye occurs through contact with M. bovis-infected secretions. This could be directly through face flies, or indirectly by contacting a contaminated object such as a fence or a feeder.
Face flies are the primary vector for spreading pinkeye, and by traveling to several different animals a day, there is potential for rapid spread of pinkeye throughout an entire herd. The flies can be infected with M. bovisfor up to three days following feeding on infected material.
Clinical signs
The peak of infection rate is usually around three to four weeks after an initial outbreak. There are four stages of the disease, ranging from light sensitivity to blindness.
Extreme discomfort or inability to visually find food can cause lack of appetite, decreased weight gain, and lowered milk production. The University of Tennessee Extension estimates a loss of 40 pounds at weaning and discounted prices at market for cattle affected by pinkeye.
Most ulcers on the cornea will heal without loss of vision, but severe cases can result in total blindness. Recovery from pinkeye usually takes three to four weeks.
Stage one of affected eyes causes excessive tearing and increased photosensitivity. The white portion of the eye will turn red from inflammation and a small ulcer, appearing as a small white spot, will develop in the middle of the cornea. The eye will also have a cloudy appearance.
In the progressing next stage, the ulcer will spread across the cornea and cloudiness will increase. Blood vessels will grow across the cornea in an attempt to help heal the eye, and the cornea will have a pink coloring, hence the term pinkeye.
Stage three will continue to see ulcer growth over most of the cornea and the interior of the eye will fill with white blood cells, giving the eye a yellow appearance.
In the final stage of pinkeye, the ulcer will completely cover the cornea and form adhesions, even after healing. Recommended treatment for stage four of pinkeye is to remove the eye.
After the ulcer has healed after stages one through three, the blood vessels will recede, but the eye may continue to have a cloudy blue color for a brief period. The eye will eventually clear up, but a white scar will remain that will impede vision.
Treatment and prevention
If detected early enough, treatment of pinkeye will be successful and may help prevent the spread of the disease further. Infected animals should be separated from the herd and treated with antibiotics or a veterinarian-recommended drug. Sprays and topical ointments must be applied several times a day in order to be effective, which is not a realistic possibility for many producers.
Protecting the eye from UV rays will assist in healing, and the easiest way to do so is to cover the eye with a patch.
Prevention may be time consuming, but management is the most effective method of disease control. Proper animal nutrition and herd immunity increases herd health and decreases disease incidence.
A preventative vaccination program and environmental management will assist in disease deterrence. Clipping pastures to prevent seed-head development and suitable grazing can reduce irritation to the eyes. Check feeders and fences for sharp edges or broken wires that could scratch the cornea. Implementing a fly control program will reduce fly populations and decrease rapid spread.
Although vaccination is a part of pinkeye prevention, numerous strains of M. bovishave caused for vaccinations to not be totally effective, which is why a combination of management practices is necessary. Pinkeye can hit hard economically, and prevention is key in order to avoid treatment costs and decreased cattle efficiency. — Anna Miller, WLJ correspondent
