Abstract
Simple SummaryAnticoagulant rodenticides are a mainstay of rodent management in many domestic, municipal, agricultural, and conservation settings. Anticoagulant poisoning has poor welfare outcomes for mammals and birds and, worldwide, this means potentially very large numbers of animals are poisoned annually consequent (intended or not) to rodenticide use. Critical differences in use patterns of anticoagulants applied for ongoing rodent control, versus application for rodent eradication especially on islands, have clear implications for animal welfare costs measured as cumulative number of animals affected over time. Here we outline these differences and discuss how animal welfare considerations can be weighed in decisions to use anticoagulant rodenticides for island eradication attempts.Anticoagulant rodenticides are used to manage rodents in domestic, municipal, agricultural, and conservation settings. In mammals and birds, anticoagulant poisoning causes extensive hemorrhagic disruption, with the primary cause of death being severe internal bleeding occurring over days. The combined severity and duration of these effects represent poor welfare outcomes for poisoned animals. Noting a lack of formal estimates of numbers of rodents and nontarget animals killed by anticoagulant poisoning, the ready availability and worldwide use of anticoagulants suggest that very large numbers of animals are affected globally. Scrutiny of this rodent control method from scientific, public, and regulatory perspectives is being driven largely by mounting evidence of environmental transfer of residual anticoagulants resulting in harmful exposure in wild or domestic animals, but there is also nascent concern for the welfare of targeted rodents. Rodent control incurs a cumulative ledger of animal welfare costs over time as target populations reduced by poisoning eventually recover to an extent requiring another reduction. This ‘rolling toll’ presents a critical contrast to the animal welfare accountancy ledger for eradication scenarios, where rodent populations can be completely removed by methods including anticoagulant use and then kept from coming back (e.g., on islands). Successful eradications remove any future need to control rodents and to incur the associated animal welfare costs.
Highlights
Simple Summary: Anticoagulant rodenticides are a mainstay of rodent management in many domestic, municipal, agricultural, and conservation settings
We focus on animal welfare considerations with respect to the use of anticoagulant rodenticides and how these considerations differ in the contexts of rodent control versus rodent eradication
Many people are familiar with the anticoagulant warfarin as an orally administered human medicine which acts as a blood thinner to prevent thrombosis
Summary
Many people are familiar with the anticoagulant warfarin as an orally administered human medicine which acts as a blood thinner to prevent thrombosis. Warfarin is one of a family of anticoagulant compounds based on a ‘coumarin’. The range of different anticoagulant compounds previously and currently used as rodenticides can be classified as indandiones or coumarins by ‘core’ chemical structure, and as first-generation (FGAR) or second-generation (SGAR) according to when they were first available as rodenticides (Figure 1). The development of heritable resistance to FGARs in some Norway rat populations, in the United Kingdom and Europe (e.g., [17]), saw declining efficacy of FGAR bait products, which prompted development and marketing of the more toxic SGARs in the 1970s [18]. The most potent SGAR compounds, brodifacoum, remain effective against rodent populations that have developed resistance to other anticoagulants [19]
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