title: Effect of treatment with an ivermectin sustained-release bolus on productivity of stocker beef calves.
abstract: Three groups of 30 crossbred beef steers, 8-10 months of age and ranging in weight from 158 to 320 kg, were used to compare effects of treatment with an ivermectin sustained-release bolus or two ivermectin injectable treatments on parasite control and productivity in relation to untreated controls during a 168 day winter-spring grazing period. Each group of 30 consisted of five cattle on each of six separate 1.6 ha pastures. Treatments on Day 0 (12 December) were: Group 1: untreated controls; Group 2: ivermectin injectable at 200 micrograms kg-1 bodyweight, s.c., on Day 0 and Day 56; Group 3: ivermectin sustained-release bolus to deliver ivermectin at 12 mg day-1 over approximately 135 days. All cattle were weighed at 28 day intervals and fecal samples were collected for egg per gram counts (EPG). Geometric mean EPG for Group 3 remained consistently less than 1.0 after Day 0 and were highest (2.4) on Day 168. All group EPG were significantly different (P < 0.01) by Day 56, and EPG of Group 2 had increased to 10.5 following initial treatment and to 42.8 on Day 112. With the exception of a low mean EPG of 6.8 for Group 1 on Day 112, EPG of the group were consistently highest (range 24.9-36.0) to the end of the experiment. Ostertagia ostertagi was predominant, along with smaller proportions of Haemonchus placei and Cooperia spp. Throughout the experiment Group 3 had highest liveweights and gains that were most often different from those of Group 1 at P < 0.01 or greater.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Veterinary Science, Louisiana Agricultural Experiment Station, LSU Agricultural Center, Baton Rouge 70803-6002, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Williams
authors.forename: A F
authors.initials: AF
authors.lastname: Loyacano
authors.forename: S D
authors.initials: SD
authors.lastname: Broussard
authors.forename: D F
authors.initials: DF
authors.lastname: Coombs
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000517:prevention & control*; D003692:Delayed-Action Preparations; D005243:Feces / Q000469:parasitology; D007559:Ivermectin / Q000008:administration & dosage*; D010270:Parasite Egg Count; D012621:Seasons; D014252:Trichostrongyloidiasis / Q000517:prevention & control / Q000662:veterinary*; D015430:Weight Gain
chemical_list: D003692:Delayed-Action Preparations; D007559:Ivermectin