Efficiency and safety of methidathion applied as a pour-on systemic insecticide for control of cattle lice.
Methidathion applied to cattle as a pour-on insecticide for control of lice (predominantly Linognathus vituli, but also Haematopinus eurysternus and Damalinia bovis) caused a reduction in the lice population of approximately 98% to 99% in laboratory trials at the minimum recommended dose of 4 mg/kg and a 98.8% to 100% efficiency was achieved in field trials. In a comparative efficiency trial in the laboratory methidathion at 3.5 to 5 mg/kg reduced the lice population by 98.8% to 99%, fenthion by 98.5% at 4.5 mg/kg and famphur by 99.7% at 16.5 mg/kg. Methidathion was tolerated by calves aged 15 to 20 weeks at dose rates up to 40 mg/kg indicating an approximate 7 fold safety margin, but 1 of 4 calves treated at 50 mg/kg died following treatment. Treatment with fenthion at 50 mg/kg, 7.4 times the average recommended rate, famphur at 75 mg/kg, 3 times the average rate and chlorpyrifos at 85 mg/kg, 5 times average rate, caused reductions in whole blood cholinesterase activity of 52%, 27% and 47% respectively which were similar to the reductions in cholinesterase activity found in calves treated with methidathion at similar levels above the recommended commercial dose rates. It was found that 2 day old calves were more sensitive to treatment with methidathion than calves 9 or 16 days old. A further 11,900 cattle of varying age, breed and sex were treated with methidathion under field conditions at the recommended rate of 4 to 8 mg/kg, and 534 cattle were treated at 24 mg/kg without any signs of toxicity.
D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy*; D004390:Chlorpyrifos / Q000008:administration & dosage / Q000592:standards / Q000627:therapeutic use; D004341:Drug Evaluation; D005284:Fenthion / Q000008:administration & dosage / Q000592:standards / Q000627:therapeutic use; D007306:Insecticides / Q000008:administration & dosage / Q000592:standards / Q000627:therapeutic use*; D010373:Lice Infestations / Q000188:drug therapy / Q000662:veterinary*; D063086:Organothiophosphates; D009946:Organothiophosphorus Compounds / Q000008:administration & dosage / Q000592:standards / Q000627:therapeutic use*; D013449:Sulfonamides / Q000008:administration & dosage / Q000592:standards / Q000627:therapeutic use
D007306:Insecticides; D063086:Organothiophosphates; D009946:Organothiophosphorus Compounds; D013449:Sulfonamides; C004992:famophos; D005284:Fenthion; D004390:Chlorpyrifos; C005828:methidathion