Biting flies that congregate on the teat ends of heifers are more than just a nuisance.

"Research has shown that horn flies transmit mastitis-causing bacteria as they feed on teat ends, causing lacerations of the tissue," say Dr. Stephen Nickerson, professor of animal and dairy science at the University of Georgia, and Dr. William Owens, professor at Louisiana State University Agricultural Center. "Such lesions become an ideal place for bacteria to colonize and eventually enter into the developing udder."

In fact, the incidence of mastitis infection is 70% in heifers with teat scabs and abrasions caused by flies, compared to 40% in heifers without these problems.

The good news is that mastitis infections can be minimized with appropriate fly control. Researchers have examined ways to do this.

In one study conducted during the spring and summer in Louisiana, insecticide tail tags reduced fly populations by 60% during the first two months after placement. Animals fitted with tags also had a lower incidence of new intramammary infections during the first two months after placement compared to controls.

"In animals with tags, the incidence increased from 8.6 to 15% over two months, while incidence increased from 17.2 to 52.4 % in controls," say Nickerson and Owens.

Keeping the incidence of heifer mastitis under control is important to future milk production.

"Louisiana researchers found that if bred heifers infected with Staphylococcus aureus were left untreated, they produced 10% less milk in early lactation than those receiving therapy," say Nickerson and Owens.

The DCHA Gold Standards II advocate for practices that control internal and external parasites, such as pesky biting flies. Control measures will vary based on your geography, so be sure to consult with your herd veterinarian for appropriate fly-control measures to use on your operation.

Source: Dairy Calf & Heifer Association