Ivermectin Bolus, and Collar, Spray, and Pour-On Applications of Amitraz for Lice Control on Beef Cattle, 1987
Authors: Lloyd J. E. , Kumar R. 
Published: March 2022

Experimental steer and heifer calves were of mixed breeds and originated in eastern Wyoming. Cattle that received amitraz treatments were housed in separate pens in groups of 6 animals each. Cattle that received the ivermectin bolus were isolated in 6 separate pens. Two pens of 6 cattle each served as untreated, controls for the amitraz treatments, and 6 additional isolated cattle served as untreated, controls for evaluation of ivermectin bolus. The cattle were naturally infested with the cattle biting louse, Bovicola bovis, the longnosed cattle louse, Linognathus vituli, and the little blue cattle louse, Solenopotes capillatus. Hair was parted and lice density was estimated by observing and recording the number of each species at sample sites on the host. In the evaluation of amitraz, body regions examined were: poll, head, shoulder, and topline. One 15 cm sample site was located across the occipital area directly behind the poll. The equivalent of 3, 15 cm sample sites were located on the head, shoulder, and topline. Sample sites on the head were 1, 15 cm hairpart on either side of the face from the corner of the mouth toward the base of the ear and 2, 7.5 cm hairparts on either side of the muzzle. Sample sites on the shoulder were 3, 15 cm vertical parts on the right side of the body. Sample sites on the topline were located on the right side of the animal ca. 25 cm posterior to the withers and 25 cm anterior to the hip bone. These sites consisted of 3 vertical 15 cm hairparts ca. 15 cm apart. In the evaluation of ivermectin bolus, slightly larger body regions were examined for lice. The body regions were: one 5 × 15 cm area on the topline, one 5 × 15 cm area on the withers, two 10 × 15 cm areas surrounding the right and left eyes, two 5 × 10 cm areas on the right and left cheeks, one 5 × 25 cm area on the muzzle, and one 5 × 15 cm area on the dewlap. Following pretreatment lice counts, the pens of cattle were ranked by percentage of animals infested. The 5 most heavily infested pens were randomly assigned to one of 5 amitraz treatments, then the remaining 5 pens were randomly assigned. Animals that were individually housed were ranked according to lice density and divided into pairs of approximately equal lice density. The members of the pairs were then assigned randomly to either the ivermectin bolus or no treatment. Amitraz treatments, which were applied in mid Jan, were: (1) amitraz collars, 90 cm long and 2.5 cm wide, installed around the neck of each animal; (2) amitraz pour-on, prepared from 1.9 ml of 12.5% Taktic® EC/CR 18040/Z and 98.1 ml of Mazola® corn oil applied from poll to tail head at 100 ml per animal; (3) 0.025% Taktic® EC/CR 18040/Z, amitraz spray, at 1 qt per animal and 80 psi; (4) 0.025% Taktic® EC/ CR 15875, amitraz spray, at 1 qt per animal and 80 psi; and (5) untreated animals. In mid Feb experimental ivermectin boluses (L-640, 471-284C-001R) were idministered by means of a balling gun to six animals at the rate of one bolus per individual. Bolused animals were checked weekly for bolus retention.