Introduction
In addition to documented losses in production due to lower weaning weights and reduced milk production in cattle (Kunz et al., 1991), horn flies (Haematobia irritans) have been linked to the occurrence of Staphylococcus aureus mastitis in dairy and beef heifers (Nickerson et al., 2000; Owens et al., 1998; Owens et al., 2000). These infections can result in chronic cases of mastitis that are refractory to treatment in adult cows and can cause reduced production, increased cull rates, and elevated somatic cell counts in dairy cows and heifers (Nickerson et al., 1995). In addition, presence of infection can result in reduced weaning weights of calves in beef cattle (Nickerson et al., 2000). Previous studies (Foil et al., 1998; Owens et al., 2000) indicate that the threshold number for flies is lower (approximately 50 per animal) for mastitis in heifers than threshold numbers (approximately 200 per animal) for meat and milk production losses in adult beef and dairy cows.
Practical control measures for dairy and beef heifers are needed that can manage horn flies during the peak fly months and prevent establishment of Staph. aureus in heifer mammary glands. This study describes the combination of a pour-on insecticide containing eprinomectin (Eprinex®) with insecticide (diazinon 40%) impregnated ear tags (Patriot®) to control horn fly numbers and prevent intramammary infections in Jersey heifers during peak fly months. A Staph. aureus vaccine was also evaluated to determine its effect on control of Staph. aureus mastitis in heifers.
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Methods
Sixty Jersey heifers 5 to 15 months of age were divided into three groups in early April at the beginning of fly season. Group I received no fly control and no vaccination, Group II received pour-on treatment (Eprinex®) every two weeks for three treatments and were then fitted with ear tags (Patriot®) in each ear after the third pour-on treatment. Group III received no fly control and was vaccinated with a Staph. aureus bacterin (Lysigen®), at day 0, day 14, and every 6 months thereafter.
Horn fly numbers were monitored at least weekly. Secretion samples or teat canal swabs for bacteriology were collected from all animals at the start of the study and at least once per month thereafter. Similarly, teat ends were examined for scab formation on a monthly basis. Secretion samples (0.01 ml) were plated to bovine blood agar plates. If no secretion was present, a streak canal swab was obtained and agitated in 0.5 ml of saline, and 0.1 ml was plated to bovine blood agar. Agar plates were incubated at 37°C for up to 48 hr. Organisms were identified using standard methods as outlined by the National Mastitis Council (1999).
Results and Discussion
Horn fly numbers for the three groups are in Figure 1. Fly numbers were reduced to approximately 5 to 10/cow by the initial pour-on treatment and remained low for approximately two weeks. Fly numbers in the control and vaccine groups remained at approximately 50/animal for the first week, then began to climb to greater than 100 per heifer and remained above 100 to 200 per heifer throughout the study.
Figure 1. Horn fly numbers for the three heifer groups. Control (untreated), Vaccine (vaccinated with Lysigen), and Treated (Eprinex® pour-on followed by Patriot® ear tags).
As fly numbers in the pour-on-treated groups began to slowly increase, a second pour-on treatment was given two weeks after the first. Again, fly numbers dropped below 5 to 10 per heifer and remained low for approximately one week and then begin to climb slowly. Two weeks after the second treatment, a third pour-on was given, and all the heifers in the treatment group were fitted with ear tags. After fitting with ear tags, fly numbers in the treatment group remained low (below 25 per animal) throughout the study period of 19 weeks. The combination of a pour-on treatment with application of ear tags has been shown to provide excellent horn fly control in beef cattle (Kunz et al., 1991).
Bacteriology results for the three heifer groups are in Tables 1 and 2. Heifers treated with the pour-on/fly tag combination had substantially reduced incidence of observable teat end scabs and new Staph. aureus intramammary infections (IMI) compared with vaccinated and control heifers that received no fly control. Heifers that were vaccinated with a Staph. aureus whole cell bacterin had fewer new Staph. aureus IMI than control heifers but more than the group with fly control, indicating that vaccination had some beneficial effect on new infections but was less effective than fly control. The incidence of transient infections (infections that were only present for one sampling and then resolved spontaneously) was also higher in the control and vaccinated groups. Staphylococcus species other than Staph. aureus (CNS) were also observed. There was substantial variability among the treatment groups for existing CNS infections; however, no effect of fly control on new CNS IMI was observed, indicating that horn flies may not be a vector in the spread of CNS infections.
Table 1. Effect of horn fly control on Staph. aureus IMI in heifers.
|
Group I |
Group II |
Group III |
|
|
Existing IMI |
2 (2) |
3 (5) |
3 (5) |
|
New IMI |
21 (18) |
2 (3) |
7 (11) |
|
Transient IMI |
15 (13) |
0 (0) |
14 (22) |
*Number in ( ) is the % of quarters with Staph. aureus IMI.
Table 2. Effect of horn fly control on the number of Staphylococcus species IMI.
|
|
Group I |
Group II |
Group III |
|
Existing IMI |
30 (26) |
19 (32) |
6 (9) |
|
New IMI |
30 (26) |
19 (32) |
14 (22) |
|
Transient IMI |
11 (9) |
0 (0) |
11 (17) |
*Number in ( ) is the % of quarters with Staph. spp. IMI.
Summary
To determine the effectiveness of a pour-on and ear tag combination for controlling horn flies and preventing Staphylococcus aureus mastitis in dairy heifers, 60 Jersey heifers 5 to 15 months of age were divided into three groups. Group I received no fly control and no vaccination, Group II received pour-on treatment (Eprinex®) every two weeks for three treatments and were then fitted with ear tags (Patriot®) in each ear after the third pour-on treatment. Group III received no fly control and was vaccinated with a Staph. aureus bacterin (Lysigen®), at day 0, day 14, and every 6 months thereafter. All heifers were sampled for bacteriology prior to the study and once a month thereafter. Fly numbers were monitored weekly. The incidence of new Staph. aureus infections was greatly reduced in the fly control group compared with the control group (3 vs. 18% new infections). Vaccination with no fly control reduced new infections overall (11 vs. 18%) but was less effective than fly control. A combination of a pour-on product and ear tags proved to be highly effective in reducing both horn fly numbers and new Staph. aureus infections compared with either vaccination or no control. Vaccination was of some benefit and should be considered in conjunction with fly control for dairy herds at risk from heifer mastitis due to horn fly infestations.
Author Information
William E. Owens and Corinne H. Ray, Louisiana State University Agricultural Center
Stephen C. Nickerson, University of Georgia
References
Foil L.D., Strother G.R., Hawkins J.A., Gross S.J., Coombs D.F., Derouen S.M., Wyatt W.E., Kuykendall L.K., Spears B.G. Jr. The use of IVOMEC® (Ivermectin) pour-on and permethrin ear tags for horn fly control. Southwestern Entomologist 23:317-323, 1998.
Kunz S.E., Murrell K.D., Lamber G., James L.F., Terrill C.E. Estimated losses of livestock to pests. In D. Pimental, ed. CRC Handbook of Pest Management in Agriculture, Vol. 1. CRC Press, Boca Raton, FL 1991, pp. 69-98.
National Mastitis Council Inc. Laboratory and Field Handbook on Bovine Mastitis. Arlington, VA. 1999.
Nickerson S.C., Owens W.E., Boddie R.L. Mastitis in dairy heifers: Initial studies on prevalence and control. J. Dairy Sci. 78:1607-1618, 1995.
Nickerson S.C., Owens W.E., DeRouen S.M. Mastitis prevalence in first calf beef heifers and effect on calf weaning weight. Large Anim. Pract. 21:20-23, 2000.
Owens W.E., Oliver S.P., Gillespie B.E., Ray C.H., Nickerson S.C. Role of horn flies (Haematobia irritans) in Staphylococcus aureus-induced mastitis in dairy heifers. AJVR 59:1122-1124,1998.
Owens W.E., Nickerson S.C., Boddie R.L. The effect of methoprene on horn fly numbers and mastitis in dairy heifers. Large Anim. Pract. 21:26-28, 2000.