Pinkeye in cattle costly
August 12, 2013
Pinkeye costs stockman thousands of dollars every year due to poor weight gains in affected animals, drop in milk production, cost of drugs and labor in treating infections, prices docked at sale time because of eye damage or blindness. Pain from the diseased eye reduces appetite. Severe cases may permanently damage the eye or rupture it. An animal blind in one or both eyes can be dangerous to handle.
Russ Daly, DVM, Extension Veterinarian/Associate Professor, South Dakota State University, says there are not a lot of consistently effective ways to prevent pinkeye or any new "silver bullets" for treatment. Some years are more challenging, due to different environmental conditions.
"There are some unpredictable years, as well. We have gotten some rain this year in parts of South Dakota so there is a lot of grass. As a result, we warn our producers that it could be a bad year for pinkeye because of irritation to eyes from tall grass and insects, but in reality there are many factors that affect occurrence of pinkeye from herd to herd and year to year. Sometimes when we expect a bad year for pinkeye, it doesn't turn out that way. Pinkeye has been an elusive disease to characterize," he says.
"Anything that irritates the eye or injures the surface of the cornea (such as tall grass, face flies and dust) can be predisposing factors. Intense UV light in summer or even in the winter reflected off snow, are some of the factors that are difficult to control," says Daly.
There are several types of bacteria implicated in eye infections. "In years past we only knew of one causative agent, Moraxella bovis. Now we have better molecular diagnostic techniques and can more readily differentiate these bacteria and tell them apart. At SDSU we've recently started using a computerized instrument that takes a lot of the time and guesswork out of identifying these," he says.
Moraxella bovis was traditionally considered the culprit, and then some other strains were identified, including Moraxella ovis. For awhile this was referred to as the sheep strain because it was first identified in sheep, but it also is found in cattle. "Microbiologists now call this bacteria Moraxella bovoculi. Even though other strains have been identified, Moraxella bovis is probably the most common pathogen causing pinkeye in cattle. But we have to realize that even within Moraxella bovis there are many different strains," says Daly.
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This may be one reason the commercial vaccine for pinkeye doesn't always give adequate protection. The strain that might be associated with eye problems in your calves this year may be a different one than what is in the vaccine.
"I think the majority of producers in our area do vaccinate for pinkeye – at least the calves going out to summer pasture. A popular strategy has been to have autogenous vaccines created from strains of the bacteria that have been previously found on their own farm. Many people feel these vaccines are fairly effective, but I am more skeptical. Vaccines sometimes get too much credit for preventing a problem. We may vaccinate a group of cattle and they don't get the disease, but it might have been a better year and they wouldn't have gotten pinkeye that year anyway. It's more than just the bug and the animal; there are other factors that play a role," he explains.
"If a certain vaccine works well for a ranch operation, that's great, and they should keep using it, but we know there are many vaccine failures, too. In a recent study in a university herd that had tremendous pinkeye problems every year, half the cattle were vaccinated and the other half left unvaccinated. The discouraging result was that there wasn't any difference between the two groups. They had just as much pinkeye in the vaccinated animals as they did in the unvaccinated group," says Daly.
Fly control may make a difference, especially on a bad fly year. Flies can be a source of irritation, and a means of bacterial spread between animals. The face fly has sharp microscopic teeth on the end of its tongue – to irritate the eye, making it water. This gives the fly access to the mainstay of its diet, the protein-rich eye secretions. Pinkeye bacteria can readily gain access to the eye via the tiny wounds in the cornea. The scrapes reduce the eye's protective defenses. If flies scrape an infected eye and then move to another animal, they transmit the bacteria to the next animal.
Insecticide ear tags are helpful to reduce fly numbers but flies may develop resistance to commonly-used chemicals. "Fly tags need to be used properly in order to minimize the resistance problems and maximize their effectiveness. They have a relatively short window of effectiveness, so you should put them in as close to the fly season as possible. Traditional wisdom was that it's also important to periodically switch products in subsequent years. If you use just one type for years the flies on your ranch may become resistant to that product," says Daly.
The earlier you can treat pinkeye, the better, before major damage is done to the eye. Even with a serious case that has deep ulcers, the eye may be saved if you treat it before the eye ruptures. "In general, the antibiotics we've used for many years are still working well for treating pinkeye. The long-acting oxytetracycline is typically a first choice. There are some treatment failures, however, which necessitate other antibiotic choices. Your local veterinarian is the best source of information about treatment choices for pinkeye," says Daly.
An additional treatment sometimes used when the eye is already damaged consists of a subconjunctival injection of antibiotic directly into the outer layer of the surface of the eyeball. "This procedure should only be done by a veterinarian or by the producer after instruction/training by a veterinarian – to do it safely and properly so the antibiotic will leak slowly out and bathe the eye with the antibiotic," he says
Some producers inject antibiotic beneath the inner surface of the lower eyelid. Both of these methods are more helpful than applying topical medication into the eye; those are quickly washed out by tears. The injected antibiotic not only leaks out slowly over the eye but may get into the local blood circulation around the eye, which also helps.
The eye needs protection as it heals. You don't want irritation from flies, dust, tall grass, etc. and you don't want the eye injured if the animal runs into something because it can't see. Commercial patches are often used, and sometimes the eyelids are sutured shut. "Suturing should not be attempted without veterinary instruction. Suture material can be used that will degrade after 2 or 3 weeks; this is long enough to give the eye a chance to heal to where it no longer needs protected," explains Daly.
"Fortunately, cattle have very tough corneas and heal pretty well. There will be an occasional case in which we do lose the eye (if it wasn't treated in time), but for most calves it won't be a problem if the eye heals with a little bit of a scar. It doesn't affect vision or long-term performance," says Daly.
"A bigger issue is in cows or bulls if they end up with a large pinkeye scar and reduced eyesight on that side. This can make them more flighty. Bulls are very visual in their breeding, so anything that affects their eyesight can be serious. Cows with partial blindness can be spooky and unpredictable," he says. If a cow or bull can be treated for pinkeye in a timely manner the eye usually heals with very little blemish; you don't want to neglect a case of pinkeye and end up with a vision problem. F