1a.Objectives (from AD-416)
To determine the level of ivermectin in the blood serum of pastured cattle that are provided with free-access to a solid, cooked protein supplement that is medicated with ivermectin.
1b.Approach (from AD-416)
Cattle will be placed in a 17-acre pasture and allowed to freely range the entire pasture. A single tub containing an ivermectin-medicated protein block and/or a single tub containing an ivermectin-medicated mineral block will be placed inside a central penning area supplied with water. The protein block and/or mineral block(s) will be weighed prior to allowing cattle access. Once the cattle are allowed access to the treatment block(s), the blocks will be weighed twice per week to determine (by weight) the quantity of material that is being taken in by the cattle. Once per week the cattle will be placed in a chute and a blood sample will be obtained from the jugular vein of each animal in separate vacuum tubes. Blood samples will then be processed to obtain the serum from the whole-blood, and the serum will be frozen for later analysis. Serum samples will be analyzed by HPLC to determint the concentration of ivermectin in each serum sample. All data collected from the study will then be tabulated to establish the amount of medicated material they are taking in and the subsequent concentration of ivermectin in the blood system.
During an 18-week study, cattle (4 animals) were provided free-access to a solid cooked supplement protein block medicated with ivermectin to determine the level of ivermectin in the blood serum of the cattle through time. The study was conducted in the absence of cattle fever ticks to establish if ivermectin levels in the serum would remain high enough to potentially eradicate a natural population of cattle fever ticks. During the first 9 weeks, the animals were provided with the ivermectin-medicated block at a dosage rate of 100 mg of ivermectin per pound of supplement. Results from the first 9 weekly blood sampling intervals of the cattle showed that ivermectin levels ranged from 3.1 ppb at Week 1 to 12.8 ppb at Week 6. The levels were below 8 ppb, which is considered to be the minimum level at which 100% control of ticks can be expected, during 6 of the 9 weekly sampling intervals. As a result of these findings, during the second 9 weeks the dosage rate was increased to 200 mg of ivermectin per pound of supplement. Results obtained from the subsequent 9 weekly blood sampling intervals at the higher dosage showed mean ivermectin levels ranging from 31.4 ppb at Week 4 to 78.6 ppb at Week 8. Thus, the levels of ivermectin in the serum of cattle never fell below the 8 ppb level. Based on this study during the second 9 weeks of the trial, these preliminary results strongly suggest that the use of this technology has the potential to eradicate a natural population of cattle fever ticks. Further studies in the presence of ticks are warranted. We are presently initiating a field study to evaluate the technology in the presence of fever ticks to determine if eradication of a natural tick population can be achieved.
The ADODR discussed protocols and exchanged summary data with cooperators through multiple on-site visits, teleconferences, and emails.