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Texas A&M College of Veterinary Medicine & Biomedical Sciences Update

published: June 6th 2008
by: Mark Birkenfeld
source: Texas A&M University

Pink Eye, Mastitis, and Weight Loss: Flies pose a Triple Threat to Texas Beef Cattle Producers

Mark Birkenfeld

Class of 2009

Texas A&M College of Veterinary Medicine

With the long sunny days that are now upon us comes the arrival of a pesky group of insects that can wreak havoc on cattle ranchers’ profits.  Fly season is here in the Southwest, and with that comes the irritation of livestock in pastures everywhere.  While producers may be aware of the constant irritation that these flies are causing their cattle, they may not appreciate the significance of the triple threat that flies are capable of.  Flies are efficient spreaders of disease that reduce productivity leading to a significant economic impact.

The most significant disease that flies are capable of perpetuating is infectious bovine keratoconjunctivitis, IBK or pinkeye.  This disease is caused by a bacterium that can easily be carried from one affected animal to another by face flies, which commonly feed around the eyes of cattle.  Affected animals develop a corneal ulceration that takes weeks to resolve with end results ranging from a normal eye following healing to an eye that is completely blind after the syndrome regresses.  It is possible for both eyes of the same animal to be affected, doubling the trouble for producers. 

Although pinkeye does not sound too alarming, it can have a large economic impact.  In one study, researchers showed that 4 weight calves affected by pinkeye in one eye were 11 pounds lighter at weaning than those calves without pinkeye.  The study also found that calves with pinkeye in both eyes weighed 35 pounds less than uninfected calves.  With today’s prices, that could mean income reductions of about $13 and $41 per head, respectively.  Add to that the cost of treating affected animals and the economics can be alarming.  While flies are not the only risk factor that can predispose an animal to pinkeye, controlling flies should help reduce the incidence of disease within a herd and potentially alleviate the profit shortfall. 

Another disease that is spread by flies in beef cattle herds is mastitis.  Mastitis, or inflammation of the mammary gland, is caused by bacteria as well.  Flies can propagate mastitis by directly transmitting the bacteria from one affected teat to another with their mouthparts.  The result is decreased milk production in affected cows that translates to lighter calves at weaning.  Researchers re-port decreases in weaning weights ranging from seven to 12.5 percent, which equates to less profit when calves are sold.  Further, cows that get serious mastitis infections may permanently lose production in the affected quarter(s) which results in lighter weaning weights in future offspring.  Effective fly control will help limit the spread of mastitis and ease potential economic burdens.

Finally, flies are capable of decreasing production in cattle even when they are not spreading disease.  In herds with no control measures in place, fly populations may reach up to 300 flies per animal.  Each of these flies feeds 20 to 30 times per day leading to major irritation.  Animals in these environments will spend more time swatting, kicking and trying to avoid flies and less time grazing.  The decrease in grazing time has been shown to decrease weaning weights by 15 to 20 pounds, resulting in lost income for producers.

Even though flies do pose a serious threat to producers’ profitability, a large number of fly control products are available to help prevent economic losses.  These include dusts, sprays, pour-ons, tags, and feeds that can be utilized in combination to effectively control the pesky insects.  Producers should remember a few important keys when designing a fly control program.  First, do not begin using any products until the economic threshold of 100 flies per animal is reached.  Otherwise, the treatment may wear off before the peak of fly season.  Also, it will decrease the time window available for flies to develop resistance to the compound used.  Other methods to help prevent development of resistance within the fly population include removing fly tags each fall as fly populations begin to dwindle and alternating classes of compounds each year.  Another tip that aids fly control efficiency involves using a macrolide deworm-er (one that contains ivermectin, doramectin, or eprinomectin) in the spring to kill both gastrointestinal worms and fly larva. Then waiting until later in the spring when adult flies reach the economic threshold to start with other fly control methods.

Working closely with your herd veterinarian to learn the warning signs of the ‘triple threat’ associated with flies will aid in the early recognition of the diseases and can reduce the impact of lost production in the herd.  By utilizing a well-designed fly control plan, cattle producers (and cattle) everywhere can keep their cool this summer season.