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United States Department of Agriculture

Agricultural Research Service

Title: The Ivomec Sr Bolus for Control of Boophilus Annulatus (Say) (Acari: Ixodidae) on Cattle in South Texas

Authors
item MILLER, JOHN
item Davey, Ronald
item Oehler, Delbert - RETIRED ARS
item Pound, Joe
item George, John

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 24, 2001
Publication Date: N/A

Interpretive Summary: In an effort to find alternatives to expensive, labor intensive dipping procedures used in the Cattle Fever Tick Eradication Program in South Texas, we conducted a study of efficacy and residual effectiveness of the Ivomec SR Bolus. Two groups of 6 Hereford heifers infested with cattle fever ticks were held on separate, tick infested, buffel grass pastures at the Cattle Fever Tick Research Laboratory, Mission, TX. Cattle in one pasture were treated with a single bolus and those in the second pasture remained untreated. The single bolus treatment resulted in 84.4% control of engorging cattle fever tick females on treated cattle, and brief exposure of untreated sentinel cattle to ticks in the treated pasture indicated that the infestation was not eliminated by the treatment. When the trial was repeated using 2 boluses per heifer, the ivermectin treatment resulted in 99.6% control of engorged female cattle fever ticks for the 20 wk trial. No ticks were found either on the treated heifers or the sentinels that were briefly placed in the treated pasture after wk 9 of treatment. This indicates that the treatment eliminated the free-living population of cattle fever ticks in the treated pasture. From these studies, we conclude that control resulting from a single bolus is not sufficient to meet the rigid requirements of the Cattle Fever Tick Eradication Program, and, although 2 boluses per animal did eliminate the ticks from treated heifers and the pasture they were in, this treatment also would not be sufficiently efficacious for large mature cattle for it to be useful in the Cattle Fever Tick Eradication Program in South Texas.

Technical Abstract: Two groups of 6 Hereford heifers infested with Boophilus annulatus (Say) were held on separate 7 ha, tick-infested, buffel grass pastures at the Cattle Fever Tick Research Laboratory, Mission, TX. Cattle in one pasture were treated with a single Ivomec SR Bolus (ISRB) and those in a second pasture were untreated controls. The concentration of ivermectin in the serum of treated cattle reached a maximum of 8.8 +/- 0.9 ppb at 2 wk after treatment. An analysis of variance indicated a significant difference (P<0.05) in the number of engorged ticks on treated vs. untreated cattle over the 20 wk trial. The treatment provided 84.4% control of engorged B. annulatus females. Exposures of sentinel cattle found free-living ticks in the treated pasture indicating that infestation was not eliminated by the treatment. When the trial was repeated using 2 ISRB per heifer, ivermectin concentration in the serum of treated cattle reach a maximum level of 31.2 +/- 3.9 ppb at week 13 after treatment. Analysis of variance indicated a significant (P<0.05) difference in the number of engorged ticks on the treated vs. control cattle over the 20 wk trial. The use of 2 ISRB/heifer resulted in 99.6% control of engorged B. annulatus females for the 20 wk trial. No ticks were found on treated cattle 9 wk after treatment, an indication that the treatment had eliminated the free-living population in the treated pasture. From these studies, we conclude that a single ISRB is insufficient for control of B. annulatus to meet the rigid requirements of an eradication program. Although 2 boluses per animal did eliminate the ticks from treated heifers and the pasture they were in, the treatment would not be sufficiently efficacious for mature cattle (>400 kg) for it to be useful in the Cattle Fever Tick Eradication Program in South Texas.

Last Modified: 7/25/2014
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