Research Summary - 1
Control of spinose ear ticks in dairy cows with permethrin spray
| Date/Time: |
9/11/2025
17:15
|
| Author: |
Phillip Jardon |
| Clinic: |
Iowa State University |
| City, State, ZIP: |
Ames, IA 50011 |
P.W. Jardon, MS, DVM, MPVM
1
;
A. Rico, DVM
2
;
A.C. Gerry, PhD
3
;
B.M. Karle, MS
4
;
N. Silva-del-Rio, DVM, PhD
2
;
1College of Veterinary Medicine; Veterinary Diagnostic and Production Animal Medicine; Iowa State University; 1809 S Riverside Drive, Ames, IA 50011
2University of California-Davis School of Veterinary Medicine, Veterinary Teaching and Research Center, 18830 Road 112, Tulare, CA 93274
3University of California Riverside, Department of Entomology, 165 Entomology Building, Citrus Drive, Riverside, CA 92521
4821 E. South Street, Orland, CA 95963
Introduction:
The spinose ear tick (Otobius megnini) is a one-host tick found in much of North America but mostly in the arid Southwestern United States. Infestations in lactating California freestall dairies have been reported. While it is known that infestations can be irritating to cattle there has not been a study quantifying production losses in lactating dairy cattle. The objective of the present study was to evaluate the effectiveness of a 0.50% permethrin spray (Catron® IV, Elanco Animal Health) in reducing spinose ear tick infestation in lactating dairy cows and its impact on milk yield.
Materials and methods:
The trial was conducted on a 2,400-cow freestall commercial dairy in California with a known spinose ear tick infestation. The study was implemented from October to November 2024. A total of 647 Holstein cows that met the selection criteria (90–180 days in milk, ≥35 kg daily milk yield, and ≤500,000 somatic cell count) were enrolled. Eligible cows were housed in two different pens and randomly allocated within pen to either control (CON; no treatment, n = 300) or tick treatment (TT; n = 347) group based on the odd/even number of their ear tag ID. Cows assigned to treatment group received approximately 3 mL application of 0.5% permethrin spray inside each ear at study initiation and again 15 days later. Researchers evaluated tick infestation weekly using a four-point tick score (TSc: 0 = no ticks, TSc: 1 = 1–5 ticks, TSc: 2 = 6–10 ticks, TSc: 3 = >10 ticks); both ears were assessed, and the highest score from either ear was recorded as the score for that animal. Daily milk yield data were collected for four weeks, and changes in weekly milk yield averages were analyzed. An ordinal logistic mixed model was used to assess treatment effects on TSc, while a linear mixed model evaluated treatment effects in weekly milk yield. At enrollment, no significant differences were observed between groups in parity (p = 0.97), weekly milk yield (p = 0.15), days in milk (p = 0.12), or tick infestation scores (p = 0.39).
Results:
A significant treatment-by-week interaction (p < 0.01) was observed. By week 3, the distribution of TSc 0, 1, 2, and 3 was 3.6%, 3.2%, 11.7%, and 81.4% in CON vs. 80.5%, 18.0%, 1.5%, and 0% in TT, respectively. However, no significant difference was observed with treatment or treatment-by-week interaction on milk yield, with a mean milk yield of 87.3 lb/d (39.6 kg/d) (TT) and 87.5 lb/d (39.7 kg/d) (CON). Our results suggest that 0.50% permethrin spray effectively reduces spinose ear tick infestation in lactating dairy cows but does not significantly impact milk yield over four weeks.
Significance:
While this study did not show a difference in milk production, that does not mean that spinose ear tick infestations do not cause a decrease in milk production. Feed intake and body condition scores were not recorded so there could have been a difference in feed efficiency. It is also possible that the damage from the ticks was already done and could not be picked up with this study design. Ear tags were not used in this study due to the potential effect of the tags on untreated neighbors as the cows were eating at the feed bunk or were lying down in the freestalls. Approved pyrethrin ear tags may be more effective than spray as they provide continual treatment and should be evaluated in future studies.
