|Norman D. Stewart, DVM
During the hot, summer months, flies can be a significant economic challenge to dairy producers in all regions of the country. Flies both decrease cow comfort and also hurt the overall health of the animal, milk production, weight gain and ultimately, profitability.
For dairy cows on pasture, it is estimated that horn flies alone may cause decreased milk production by as much as 20 percent. Another study estimates that flies cause livestock production losses in excess of $2.26 billion annually.
Types of Flies
The most common flies affecting dairy cattle are horn, face and stable flies:
- Horn flies are found primarily on the back, where they bite into the skin and suck blood as often as 40 times a day. This results in blood loss and intense irritation.
- Face flies are found primarily on the face and have sucking mouth parts that irritate the eyes and cause increased production of tears. They feed on excess tear and mucus secretions. They also transmit a bacterium that causes pinkeye.
- Stable flies have piercing mouthparts that result in a painful bite that causes animals to stamp and kick as the flies feed around their flanks and hocks.
Fly resistance to insecticides is another challenge dairy producers may face. This occurs when products are not applied as directed by the product label. Here are some ways to minimize the risk of developing resistance:
- Administer a comprehensive (long-term) fly control program throughout the fly season, even though you may see results in the short-term.
- When ear tags lose their effectiveness, remove them and apply a final dose of a low-volume pour-on.
- Where applicable, rotate classes of insecticides from one fly season to another.
- Don't under-dose the insecticide.
Best Management Practices
So what can dairy producers do to combat these economic losses and minimize resistance? The answer is a total fly control program, and the return on investment is significant. For every $1 invested, dairy producers will see, on average, an $8 return. In these economic times, anything that produces a return on investment like this is a wise management decision.
Whether you need to evaluate your current fly control program or start a new one, here are some best management practices to consider:
- Treat animals of all ages and their premises with an insecticide.
- Use products that are effective, long-lasting and easy to administer.
- For calves and cows, apply a low-volume pour-on for rapid knockdown of the existing fly population.
- For growing replacement heifers, apply two ear tags in addition to a low-volume pour-on insecticide.
- Use an insecticide on the animal's premises, such as a microencapsulated product, that delivers superior, long-lasting control on a wide variety of surfaces in and around livestock facilities.
- Use additional fly control measures as necessary, such as back-rubbers, oilers and other devices that can be used on pasture or in the milking parlor as cows exit the facility.
- Eliminate organic debris such as wet/rotting hay, straw, feed, silage and manure. These are ideal breeding grounds for stable flies.
- If you believe a product is not working, contact the manufacturer and your animal health provider to discuss the situation and get some help.
- Reapply insecticides throughout the fly season, and always follow label directions.
As we enter August, the hottest month of the year for most of us, now is the time to evaluate your fly management program and consider these fly control strategies to help improve herd health and profitability.
¹Campbell, J.B., University of Nebraska, NebGuide G1180
² Byford, R.L. et al., J. Anim. Sci. 70:597-602
Norm Stewart is the Manager of Dairy Technical Services for Intervet/Schering-Plough Animal Health. He lives in Illinois. For more information, e-mail Dr. Stewart at: firstname.lastname@example.org.