Source: Steve Nickerson, University of Georgia
Mastitis control during the hot summer months is important to the health of mammary glands and milk quality. In northern Europe, summer mastitis, occurring during July, August, and September, is associated with an increase in biting flies that carry bacteria. This type of mastitis, caused by Trueperella pyogenes, is typically controlled using insecticidal sprays.
In the US, fly season begins as early as April and lasts through September or early October, especially in the Southeast. Following the “5-point plan” for mastitis control has led to a reduction in the level of intramammary infections; however, the importance of fly control in reducing cases of mastitis has been overlooked.
Many producers implement fly control techniques to reduce insect populations on the farm premises (barns, hutches, etc.) and on animals; however, insect pest control techniques are not applied to specifically prevent mastitis among dairy cows and heifers. With the temperature and humidity steadily rising in recent months, numbers of bloodsucking horn flies (Haematobia irritans) will increase.
This species is commonly found on the backs of dairy animals, but will also attack the teats, leading to the development of mastitis, especially among dairy heifers. Research has identified a greater prevalence of mastitis caused by Staphylococcus aureus in dairy heifers that had teat ends covered in scabs caused horn flies. Additionally, studies have shown a lower prevalence of mastitis caused by Staph. aureus among heifers in herds using fly control compared to herds not using a fly control program.
So, how is Staph. aureus spread from fly to animal and from animal to animal? Horn flies carrying Staph. aureus zero in on the teat ends of dairy heifers and suck blood from vessels below the teat skin, causing the formation of abscesses and scabs with their invasive mouth parts, subsequently depositing Staph. aureus. This places these bacteria in an opportune position to enter the teat canal and cause an intramammary infection.
Flies then serve as vectors and carry the bacteria from animal to animal, resulting in an increased prevalence of Staph. aureus mastitis. Horn flies damage teat ends: In an ongoing trial at UGA, teat ends of heifers were monitored before, during, and after fly season. At the beginning of fly season and before application of a control program, teats were populated with blood-sucking flies and many were covered with bloody scabs associated with Staph. aureus intramammary infections.
Less than 48 hours after pour-on repellent administration, fly populations were drastically decreased, and less than 2 weeks later, teats were healed and free of scabs. However, the damage had been done and Staph. aureus infections were established, which were subsequently cured with dry cow antibiotic therapy.
Overall, the prevalence of Staph. aureus intramammary infections among quarters of dairy heifers was 30%; not that uncommon in GA dairy herds. The rest of mammary quarters were infected with the coagulase-negative staph, also known as CNS (27%), and the streptococci (3%); only 40% of quarters were uninfected.
Horn flies are attracted to the navel area of heifers, which is in close proximity to the front teats. Also, the tail switch may be more effective in repelling flies from biting the rear teats. Not only do these flies provide a vector for the spread of Staph. aureus, but they are also a nuisance to the already stressed animals during hot weather.
What you can do to protect your heifers: Sanitation is key in reducing farm populations of different types of flies. Proper management of manure, water troughs, and leftover feed and hay reduce fly numbers, and may reduce the mastitis cases caused by these flies. However, maintaining a sanitary environment may not be effective in reducing all insect populations of concern to a desirable level.
Several different fly control techniques exist such as aerosols, baits, strips, foggers, dust bags, traps, oilers, insecticidal ear tags, insecticidal pour-on solutions, and feed supplementation with insect growth regulators. The use of an insecticidal pour-on every 2 wk for 6 wk followed by placement of insecticidal ear tags was found to reduce fly populations and decrease the incidence of new Staph. aureus infections in heifers by 83% in a 6-month efficacy trial at LSU.
At UGA, the use of a pour-on every 2 to 4 wk was found to drastically reduce fly populations, allowing teats to heal, and reducing two important sources of Staph. aureus: flies and scabs. While there are no techniques that are 100% effective, the use of some type of fly control is important in reducing mastitis cases in dairy heifers, and in turn, decreasing SCC when they freshen. With milk buyers’ current demand for low herd SCC, all feasible methods that lead to improvements in milk quality are essential to consider.
Don’t let flies cost you money due to increased mastitis, elevated SCC, and loss of quality product premiums when your heifers enter the milking herd.