title: Duration of anthelmintic efficacy of doramectin and ivermectin injectable solutions against naturally acquired nematode infections of cattle.
abstract: A comparison of persistent efficacy of doramectin injectable (D) and ivermectin injectable (I) was investigated under field conditions with treated permanent principal (PP) and interval-grazed principal (IGP) calves. The experiment was initiated on October 13, 1992 (day 0). Cattle used were crossbred beef heifers of 185 kg average weight and 8 to 10 months old. By random allotment, 66 calves were divided into two groups of 15 PP-D and PP-I calves for each treatment and two groups of 15 IGP-D and IGP-I calves for each treatment. Three extra or replacement calves were allotted for each group. Permanent principal calves in three replicates of five cattle per treatment grazed continuously on nematode-contaminated replicate pastures from day 0 to day 70. At 2-week intervals, i.e., days 0 to 14, 14 to 28, 28 to 42, 42 to 56 and 56 to 70, one IGP-D and one IGP-I calf was grazed with each of the respective PP-D and PP-I calf replicates and necropsied 21 days after removal from pasture. All respective PP calves and IGP calves were treated with doramectin at 200 micrograms kg-1 or ivermectin at 200 micrograms kg-1 by s.c. injection on day 0. After the day 0-14 interval, all IGP-D calves had zero egg counts. From the day 14-28 interval through the next three grazing intervals, the arithmetic mean egg counts of IGP-D calves were 18, 90, 281 and 31; those of IGP-I calves were 30, 226, 74 and 185. This suggested a persistence effect of approximately 2 to 4 weeks. In PP-D calves, egg counts reached a mean maximum at day 56 of only five eggs per gram, while counts of PP-I calves reached a peak of 40 on day 42. From the day 14-28 interval and through all subsequent intervals, arithmetic mean total worm counts from IGP-I calves were 58 to 73% greater than those in IGP-D tracers. A maximal total worm count of 4159 was observed in IGP-D calves of the day 42-56 interval; total worm counts in IGP-I calves from the day 14-28 interval through the day 42-56 interval were: 5420, 6739 and 9979, respectively. Haemonchus and Cooperia were higher in prevalence than Ostertagia in both treatments. Results of PP-D egg counts and total worm burdens in IGP-I calves indicated a high level of doramectin persistent activity for approximately 4 to 5 weeks and an advantage over persistence activity of ivermectin.
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
authors.forename: D
authors.initials: D
authors.lastname: Walstrom
mesh_terms: D000821:Animal Feed; D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage / Q000627:therapeutic use*; D002417:Cattle; D002418:Cattle Diseases; D005260:Female; D006188:Haemonchiasis / Q000188:drug therapy / Q000662:veterinary; D006189:Haemonchus / Q000302:isolation & purification; D007279:Injections, Subcutaneous; D007559:Ivermectin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use*; D009349:Nematode Infections / Q000188:drug therapy / Q000662:veterinary*; D010028:Ostertagia / Q000302:isolation & purification; D010029:Ostertagiasis / Q000188:drug therapy / Q000662:veterinary; D010270:Parasite Egg Count; D012996:Solutions; D013997:Time Factors; D014253:Trichostrongylosis / Q000188:drug therapy / Q000662:veterinary; D014254:Trichostrongylus / Q000302:isolation & purification
chemical_list: D000871:Anthelmintics; D012996:Solutions; D007559:Ivermectin; C084101:doramectin