Suchergebnisse

Brodifacoum is a second-generation anticoagulant rodenticide used widely for controlling brushtail possums (Trichosurus vulpecula) in New Zealand. We determined its toxic effects on possums to make inferences about the welfare of brodifacoum-poisoned possums. Caged possums were fed a lethal dose of brodifacoum in cereal baits then either bled and killed 4, 8, 12, 16 or 20 days later to establish the effects on blood-clotting, or observed for behavioural changes until death. Blood-clotting time was prolonged 8 days after possums first began ingesting brodifacoum and time to death was 20.7 ± 1.7 days (mean ± s.e.m.). Clinical signs of poisoning, including changed appearance, pale noses and external bleeding, appeared from 14 days after initial poisoning (7 days before death). Possums gradually became inactive and lethargic, typically crouching and lying in abnormal postures for 6 days before death. Feed intake reduced concurrently, resulting in significant loss of body weight of 5.9 ± 2.1%. All possums had widespread, usually severe, haemorrhaging. Internal haemorrhages first appeared in all possums 8 days after initial ingestion. These haemorrhages, and consequent blood loss, may cause distress, pain, weakness or sickness, and this is supported by evidence from humans and other animals. Reduced feed intake, inactivity, lethargy and the display of abnormal postures suggest that possums do experience distress for at least 6 days before death.

Context
Control of unwanted wildlife ('pest' animals) is undertaken for conservation and economic reasons, and when such animals are considered a nuisance. Such control should be undertaken using approaches that minimise, as far as possible, detrimental impacts on the welfare of the animals. Using a scientific framework based on the Five Domains model, the relative welfare impacts of pest control methods can be compared across methods and pest species.

Aims
We demonstrate the application of a modified version of this framework to evaluate the relative impacts of seven Vertebrate Toxic Agents (VTAs) used to control brushtail possums (Trichosurus vulpecula) in New Zealand. The evaluation is used to produce a ranking of the seven VTAs based on their relative impacts on possum welfare.

Methods
Scientific literature describing mode of toxic action, specific effects in possums or other animals and reports from human poisonings was collated as reference material for a panel of six experts. The panel produced a median welfare impact score ('none' to 'extreme') for each of the Five Domains. The 'Overall Grade' (1 to 8) reflected the intensity and duration of all impacts of a VTA on possums.

Key results
All VTAs evaluated have at least moderate impacts on possum welfare, lasting for at least minutes. Cyanide was assessed as having the lowest welfare impacts (median grade 4), and cholecalciferol and the anticoagulants the highest impacts (7.5 to 8). Zinc phosphide was assigned an intermediate grade (6) with high confidence. While the overall impacts of sodium fluoroacetate (1080) and phosphorus were also assessed as intermediate (6), the panel's confidence in these scores was low.

Conclusions
From an animal welfare perspective, anticoagulant poisons and cholecalciferol should be the least preferred options for controlling possums in New Zealand, as VTAs with less severe welfare impacts are available.

Implications
The results of such assessments allow animal welfare impacts to be integrated with other factors in wildlife management decision-making and policy development, and are thus useful for managers, researchers, regulators and operators. Evaluation of welfare impacts aligns with the goals and mandates of ethical wildlife control and may also be valuable in wider wildlife research and management activities.