Submitted to: Journal of Agricultural and Urban Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 12, 1997
Publication Date: N/A
Interpretive Summary: Pastured cattle were treated at 3-4 day intervals with ivermectin at either 200 ug/kg orally or 40 ug/kg by subcutaneous injection. Both treatments reduced the number of lone star ticks feeding on the cattle as compared to those on untreated cattle. The level of ivermectin in the serum of those treated orally ranged from 4-6 ppb and from 13-15 ppb for those treated by injection. The marginal effect of the oral treatment indicates that 200 ug/kg at 3-4 day intervals would be inadequate for management of field populations of lone star ticks. The inherent variability of free-choice consumption, either between animals or within animals between feeding times, means that unless cattle can be expected to use either medicated mineral daily or every other day, the oral dosage should be greater than 200 ub/kg for control of lone star ticks under field conditions. In contrast, only 40 ug/kg of ivermectin delivered by subcutaneous injection at 3-4 day intervals should provide adequate control of ticks feeding on pastured cattle. An implant or other form of sustained-release injectable that can produce 13-15 ppb ivermectin in serum should be efficacious. These results should also be applicable to the treatment of white-tailed deer for control of ticks that transmit diseases.
Technical Abstract: Pastured cattle were treated twice weekly with ivermectin either at 200 ug/kg oral or 40 ug/kg by injection. The number of lone star ticks, Amblyomma american (L.), on the treated and the untreated groups within a single herd were observed for four weeks. There was no significant (P greater than 0.05) difference in the number of unengorged, small (4-6 mm), and medium (6-8 mm) female lone star ticks on the untreated controls and those treated orally. However, the oral treatment resulted in significantly (P less than 0.05) fewer large (8 mm) females than were seen on the untreated cattle. Significantly (P less than 0.05) fewer small, medium, and large female ticks were found on the injected cattle than on the untreated controls. Interestingly, there were significantly (P less than 0.05) more unengorged females on the animals treated by injection than on those treated orally or left untreated. Animals treated orally had 4-6 ppb ivermectin in their blood serum, while those treated by injection had 13-15 ppb.