Persistent activity of injectable ivermectin in the control of the cattle tick Boophilus microplus
Cramer, L.G.; Bridi, A.A.; Amaral, N.K.; Gross, S.J.
Veterinary Record 122(25): 611-612
1988
ISSN/ISBN: 0042-4900 PMID: 3407118 Document Number: 310202
Eight tick-free Holstein calves (149.8-187.0 kg) were divided into 2 groups: untreated controls and those treated once subcutaneously with 200 micro g/kg ivermectin. Each calf was experimentally infected with 5000 B. microplus unfed larvae on days 0, 3, 5, 7, 10, 12, 14, 17, 19 and 21. Engorged female ticks dropping off the calves were collected on days 21, 24, 26, 28, 31, 33, 35, 38, 40 and 42 and counted and weighed. The arithmetic mean weight of ticks collected each day was always lower for the ivermectin-treated calves and was significantly lower on days 21, 24, 26 and 28. Statistical analysis showed the persistence of ivermectin activity within the first week after treatment, and experimental findings suggested that this effect may last for a longer period.