Control of lone star ticks on cattle with ivermectin. J. Agric. ... bovine serum. J. Assoc. Off. Anal. Chern. 72: 59. Pegram, R. G. & J. Lemche. 1985. Observations on ...
Efficacy of Daily Oral Treatments of Ivermectin Administered to Cattle Infested with Boophilus microplus (Acari: Ixodidae)1,2 Ronald B. Davey,3 J. Allen Miller,4 and John E. George4 Agriculture
Research Service, USDA, Texas, USA
ti
, J. Agric. Urban Entomol. 18(2): 127-137 (April 2001)
The efficacy of ivermectin administered orally to cattle infested with all parasitic stages of Boophilus microplus (Canestrini) ticks was evaluated. Ivermectin capsules were administered to two separate groups of cattle at a dose rate of either 25 or 50 ILg/kgfor a period of21 consecutive days. A third group of calves received a placebo capsule each day and served as a control. Although the overall control achieved at both doses of ivermectin was >99% against all parasitic stages, the 50 ILg/kg/ddose was significantly more effective than the 25 ILg/kg/ddose against each developmental stage ofthe tick. Each ivermectin treatment dose produced a significantly higher percentage reduction in female tick numbers against ticks that were adults at the time of treatment onset than was observed against immature ticks (nymphs and larvae), however the 50 ILg/kg/dtreatment was significantly more effective in reducing tick numbers, regardless ofthe developmental stage ofthe ticks. Both engorgement weight and egg mass weight of females were significantly lower in the ivermectin treated groups than were observed in the untreated group. The potential applicability for treating tick-infested cattle with different delivery systems, such as daily oral treatments, boluses, and medicated feed that contain ivermectin or other macrocydic lactone compounds is also discussed. ABSTRACT
ivermectin, Boophilus microplus, oral treatment, macrocydic lactone, cattle tick, acaricidal activity
KEY WORDS
The discovery and development of avermectin endectocides, of which ivermectin is perhaps the foremost example (Hotson 1981), has provided the opportunity for evaluation of these compounds for the control and management of livestock ectoparasites. The avermectins offer the dual advantage of having broad spectrum activity and efficacy at extremely low concentrations (Putter et al. 1981). Numerous investigations with various tick species have been conducted which demonstrate that avermectins would be excellent candidates for use in programs
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1Accepted for publication 17 August 2001. 2This paper reports the results of research only. Mention of a commercial or a proprietary product in this paper does not constitute an endorsement by the U.S. Department of Agriculture. 3Cattle Fever Tick Research Laboratory, Agricultural Research Service, UB. Department of Agriculture, Southern Plains Area, Rt. 3, Box 1010, Edinburg, Texas 78539. 4Knipling-Bushland U.S. Livestock Insects Research Laboratory, Agricultural Research Service, Southern Plains Area, 2700 Fredricksburg Road, Kerrville, Texas 78028.
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where control of the pest species is the ultimate objective (Nolan et al. 1981, Drummond et al. 1981, Lancaster et al. 1982, Horak et al. 1983, Pegram & Lemche 1985, Cramer et al. 1988, Miller et al. 1989; 1997, Taylor & Kenny 1990, and SolI et al. 1989; 1990). However, with perhaps one notable exception (Miller et al. 1999), there is a paucity of information regarding the potential applicability of avermectins in a program where eradication of the pest is the goal. The United States Boophilus Eradication Program has been in continuous operation in the continental U.S. since 1906. Presently Boophilus spp. ticks have been eradicated throughout the country, except for 8 counties that lie along the Texas-Mexico border, where a permanent quarantine is maintained by the U.S. Department of Agriculture, Animal Plant Health Inspection Service, Veterinary Services. Program operational procedures, as they are currently applied, rely solely on the use of an organophosphate (OP) acaricide, coumaphos, as the principal means of preventing the re-introduction of Boophilus ticks. Due to several factors associated with the reliance on this single acaricide, such as reregistration of the material and the widespread occurrence of OP resistance in tick populations in Mexico, there is a critical need to identify and develop alternative acaricides and treatment methods which may have potential for use in the Cattle Fever Tick Eradication Program in the United States. In the current study, the primary objective was to determine whether the sustained application of ivermectin administered to tick-infested cattle provides a standard of control that would be acceptable in an eradication program. The secondary objective was to obtain data that can be used in the future development of sustained release technologies, such as boluses or medicated feed systems for use in a systematic treatment eradication program. Materials and Methods This study was conducted at the USDA, Agricultural Research Service, Cattle Fever Tick Research Laboratory in Mission, Texas, a certified quarantine facility where research on Boophilus spp. ticks is conducted in support ofthe eradication program. Experimental design. Nine Hereford heifer calves weighing approximately 190 kg each were randomly assigned to three groups of three each. Throughout the study each calf was stanchioned individually in a 3.3 x 3.3 m stall in an open-sided bam under ambient conditions, except that no direct rainfall or sunlight reached the cattle. Fourteen days before the initiation of oral ivermectin treatments each calf was infested with ca. 5,000 B. microplus larvae that were 2-4 wk of age. Additional larval infestations of ca. 5,000 each were made at 7 d and before the beginning of oral treatments. This infestation regime provided the means for evaluating the effects of oral treatments against ticks that were in the early stages of adult development (14-d pretreatment infestation), nymphal development (7-d pretreatment infestation) and newly infesting larvae (O-d pretreatment infestation) at the time oral treatments were initiated. Engorged female ticks were collected and counted daily beginning on the first d when they began to detach from the calves (21 d after the first pretreatment infestation and 7 d after the oral treatments were initiated). The daily tick collections were continued for 28 d after the last pretreatment infestation (7 d after the oral treatments were terminated). Random samples of up to 10 females
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per day per calf (whenever possible) were saved to obtain data on the oviposition capability of the surviving ticks. Females within each sample (:s10) were weighed collectively, placed in a coded 25 x 95 mm (8-dram) shell vial with a cotton stopper and stored in an incubator at 27 ± 2°C, 92% RH, under a 12:12 [L:D]hphotoperiod and allowed to oviposit for 20 d. After oviposition was complete females were discarded and the eggs produced by females in each sample were weighed and returned to the incubator. Mter 4 wk the percentage egg hatch of each sample group was visually estimated by observing the contents of the vial under a stereo microscope with a grid background and comparing the proportion oflarvae to the proportion of unhatched eggs within the vial. When all data on daily tick counts and engorgement weight, egg mass weight, and percentage egg hatch of saved females were complete, the daily index of fecundity (IF) of the ticks recovered from each calf in each of the three groups of animals was calculated. The IF is an estimate ofthe reproductive potential of the ticks that survived to repletion following the onset of oral ivermectin treatments, and is derived from the index of reproduction (IR) formula described by Drummond et al. (1967):
No. of
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