First generation anticoagulant rodenticide persistence in large mammals and implications for wildlife management

Abstract

The use of first generation anticoagulants by the Department of Conservation (DOC) for rodent control has increased in recent years. This study estimates the likely hepatic persistence time of diphacinone in red deer, pigs and cattle exposed to a single sublethal dose, as well as coumatetralyl in red deer. Red deer were given an initial dose of either 1.5 mg/kg diphacinone or 8.25 mg/kg coumatetralyl, which equated to a similar quantity of commercially available bait for these anticoagulants. At these initial doses, the mean hepatic elimination half-life of diphacinone in red deer is estimated as 6.0 days whereas the mean estimated hepatic elimination half-life of coumatetralyl is estimated as 18.9 days. In pigs given an initial dose of 1.5 mg/kg, the mean hepatic elimination half-life is estimated as 12.4 days. Cattle were dosed with 1.5 mg/kg diphacinone in two similar trials. The results suggest that diphacinone is metabolised and distributed quite differently in cattle from the other species studied, including longer hepatic persistence. It would be valuable to investigate hepatic persistence of other anticoagulants in cattle to inform withholding periods for livestock in the case of accidental exposure.

Keywords:

• anticoagulant
• cow
• coumatetralyl
• deer
• diphacinone
• New Zealand
• pig
• persistence
• pharmacokinetics
• residues
• rodenticide

Acknowledgements

This work was funded by the New Zealand Department of Conservation (Science Investigation No. 4029). All procedures carried out on animals in this work were approved by the Lincoln University Animal Ethics Committee (Project No. 240 for the first cattle trial; Project No. 241 for the pig trial, Project No. 297 for the deer trial, and Project No. 298 for the second cattle trial). We thank Dr. Don Arthur for his expertise in carrying out the euthanasia procedures and the liver biopsies on cattle and deer. Martin Ridgeway assisted with animal handling and euthanasia. We thank Dr. Lynn Booth and Dr. Paul Chambers for providing advice to support our analysis of the results. Sincere thanks to two anonymous referees for their valuable comments on earlier versions of this paper.