Effect of potassium cyanide on behaviour and time to death in possums

Assessment of non-target risks from sodium fluoroacetate (1080), para-aminopropiophenone (PAPP) and sodium cyanide (NaCN) for fox-incursion response in Tasmania

Context Access to effective toxicants and delivery systems that target red foxes (Vulpes vulpes) are likely to be required as part of a management strategy in the event of future red fox incursions into Tasmania. Potential toxicants include sodium fluoroacetate (1080), para-aminopropiophenone (PAPP) and sodium cyanide (NaCN). Aims To assess the risk of three toxicants (1080, PAPP and NaCN) to non-target native Tasmanian mammals and birds and domestic dogs and cats. Methods We identified native Tasmanian mammal and bird species that may potentially consume fox baits, by reviewing the ecological traits of native species and by monitoring 180 buried bait stations with video cameras. We also assess the potential risk to non-target species of dying from a single standard dose of each of the three toxicants. Key results Seven native mammal and 20 native bird species have the potential to consume fox bait. All vertebrates would be susceptible to a single dose of NaCN. Consumption of a single fox bait containing 3 mg 1080 may be lethal to five native mammals, three native birds, and the domestic cat (Felis catus) and dog (Canis familiaris). Consumption of a single fox bait containing 226 mg PAPP may be lethal to the spotted-tailed quoll (Dasyurus maculatus) and the domestic cat and dog. Delivery of toxicants via a mechanical ejector would reduce non-target exposure to toxicants. Conclusions It appears that PAPP would provide a useful alternative to 1080 for use in lethal fox control in Tasmania, either in the event of an incursion or in the eradication of an established population. NaCN is not suitable for broadscale use in Tasmania because of the high susceptibility of all vertebrates to this toxicant. Nevertheless, NaCN would be useful in highly restricted areas in the event of an incursion where carcass recovery is important. The use of a mechanical ejector to target delivery of toxicants to red foxes would reduce non-target risks. Implications Our results clarify theoretical non-target risks from any future fox-poisoning programs in Tasmania and highlight the need for further research on the susceptibility of native species to PAPP as a potential alternative to 1080.

Managing and eradicating wildlife tuberculosis in New Zealand

Tuberculosis (TB) due to Mycobacterium bovis infection was first identified in brushtail possums (Trichosurus vulpecula) in New Zealand in the late 1960s. Since the early 1970s, possums in New Zealand have been controlled as part of an ongoing strategy to manage the disease in livestock. The TB management authority (TBfree New Zealand) currently implements three strategic choices for disease-related possum control: firstly TB eradication in areas selected for eradication of the disease from livestock and wildlife, secondly Free Area Protection in areas in which possums are maintained at low densities, normally along a Vector Risk Area (VRA) boundary, and thirdly Infected Herd Suppression, which includes the remaining parts of VRA where possums are targeted to minimise the infection risk to livestock. Management is primarily through a range of lethal control options. The frequency and intensity of control is driven by a requirement to reduce populations to very low levels (usually to a trap-catch index below 2%), then to hold them at or below this level for 5–10 years to ensure disease eradication.Lethal possum control is implemented using aerial- and ground-based applications, under various regulatory and operational constraints. Extensive research has been undertaken aimed at improving the efficacy and efficiency of control. Aerial applications use sodium fluoroacetate (1080) bait for controlling possums over extensive and rugged areas of forest that are difficult to access by foot. Ground-based control uses a range of toxins (primarily, a potassium cyanide-based product) and traps. In the last 5 years there has been a shift from simple possum population control to the collection of spatial data on possum presence/absence and relative density, using simple possum detection devices using global positioning system-supported data collection tools, with recovery of possum carcasses for diagnostic necropsy. Such data provide information subsequently used in predictive epidemiological models to generate a probability of TB freedom.The strategies for managing TB in New Zealand wildlife now operate on four major principles: firstly a target threshold for possum population reduction is defined and set, secondly an objective methodology is applied for assessing whether target reductions have been achieved, thirdly effective control tools for achieving possum population reductions are used, and fourthly the necessary legislative support is in place to ensure compliance. TBfree New Zealand's possum control programme meets these requirements, providing an excellent example of an effective pest and disease control programme.

Research on vertebrate pesticides and traps: do wild animals benefit?

New Zealand has a range of carnivorous and herbivorous mammals that were originally introduced for recreational, financial, aesthetic and biocontrol reasons, but which now pose significant threats to conservation and animal health values. Research is undertaken to develop new tools and strategies to manage these pests. Captive trials that are carried out include those to determine the toxicity of poisons, the efficacy of fertility control agents, and welfare impacts of poisons and traps. Field trials are undertaken to test the efficacy of poisons and traps, and large-scale management trials carried out to optimise control strategies. Although this research is aimed at managing animals, including killing them, we believe that there are benefits to both individual animals and animal populations that far exceed any cost of harm to individuals that are managed (often killed). We suggest that there are three levels of beneficiaries: the individuals of the pest species that are killed, the individuals in the surviving population, and the individuals and populations of other species. We provide examples of how wild animals can benefit from vertebrate pesticide and trap research.

What can pest management learn from laboratory animal ethics?

There remains a lack of a clear overarching policy framework for decision-making in pest control programmes. In comparison, ethical principles have been extensively developed for scientific procedures, such as those underlying the UK's Animals (Scientific Procedures) Act 1986. This paper assesses the extent to which the principles and methodology underlying the act and secondary guidance could be used to provide principles of rodent management. Useful principles include that any programme has a legitimate purpose; that methods are used only if the harms are outweighed by the benefits; that harms are minimised by refinement, replacement and reduction and that there is personal responsibility. The usefulness and implications for pest control of each principle and the overall approach are discussed.

Advancing a humane alternative to sodium fluoroacetate (1080) for wildlife management - welfare and wallaby control

There is controversy regarding the continued use of sodium fluoroacetate (1080) and questions regarding its humaneness. Two studies on captive animals were undertaken to assess the effectiveness and humaneness of Feratox© cyanide pellets for culling Dama and Bennett's wallabies as an alternative to 1080. Following ingestion of the toxic pellets by the wallabies the effects of cyanide were closely observed. Feratox has few undesirable signs from the welfare perspective and on the basis of humanness offers a preferred alternative to other vertebrate toxins, including 1080, for the control of wallabies.

Behaviour and time to unconsciousness of brushtail possums (Trichosurus vulpecula) after a lethal or sublethal dose of 1080

Context. Sodium fluoroacetate (1080) is a vertebrate pesticide used in several countries, including New Zealand, where it is the main pesticide for controlling brushtail possums (Trichosurus vulpecula) – a significant agricultural and conservation pest. There is growing concern internationally about the impacts of vertebrate pesticides, including 1080, on pest animal welfare. Aims. Behavioural changes and time to loss of consciousness of possums after 1080 ingestion in carrot baits were determined to compare the animal welfare impacts with other possum pesticides. Methods. Eight lethally dosed possums and eight that consumed a dose intended to be sublethal were observed until death or recovery but not handled. Another nine lethally dosed possums were handled to determine responses to stimuli, indicating time to loss of consciousness. Key results. Unhandled, lethally dosed possums died after 11 h 26 min ± 1 h 55 min (mean ± s.e.m.). Half had abnormal appearances and postures 1 h 50 min ± 9 min after consuming baits. Seven showed retching, and three vomited, over 27 ± 12 min from 2 h 53 min ± 13 min. Lack of coordination began 3 h 37 min ± 32 min after dosing, then possums spent most of the time until death lying, showing spasms and tremors. Five showed seizures while lying prostrate. Possums receiving a nominally sublethal dose all showed signs of poisoning, including abnormal postures, lethargy, lack coordination, retching, spasms or tremors, and a cessation of grooming, feeding and activity. One died 18 h 15 min after dosing, experiencing two seizures within 30 min of death. Response to handling, indicating total loss of consciousness, was lost in two possums before death. Conclusions. Possums ingesting a lethal dose of 1080 experienced ~9.5 h of changed behaviour and lost consciousness close to death, although awareness was likely reduced sometime beforehand. Possums ingesting a nominally sublethal dose experienced some effects of poisoning. Implications. These impacts are intermediate compared with other possum pesticides in New Zealand. Nevertheless, the potential for consciousness during and after retching and seizures is undesirable for animal welfare. Further work is encouraged on alternatives to 1080 and means of reducing its impact on animal welfare.

Behavioural, biochemical, and pathological responses of possums (Trichosurus vulpecula) poisoned with phosphorus paste

AIM

To investigate the behavioural, biochemical and pathological responses of possums following poisoning with phosphorus paste, in order to assess the implications for the welfare of possums.

METHODS

After ingestion of phosphorus paste by wild-caught possums (18 high dose, nine low dose, and 12 non-poisoned controls), behavioural observations were made at 15-min intervals for 24 h or until death. Serum biochemistry, and gross and microscopic pathology were assessed at 3-hourly intervals in a further 21 possums.

RESULTS

Possums that ingested phosphorus paste developed an abnormal posture (high incidence of crouching after 4-8 h), mild congestion of the gastric mucosa, and elevated levels of creatine kinase (CK) in serum after 3-6 h. Retching was observed in 67% possums, and 44% vomited at least once. Possums were prostrate from about 18 h after eating the poison, and the response to handling, an indicator of consciousness, was lost at about 24 h, followed by death at 25 h.

CONCLUSION

The main welfare concern was the possibility of discomfort or pain caused by the congestion of the gastric mucosa, as indicated by the crouched posture adopted by poisoned possums. Retching and vomiting may also have caused pain and distress. The degree of pain or discomfort would depend on the degree of congestion of the gastric mucosa, which was typically mild, and on the duration and severity of retching and vomiting, which were typically short and mild. Possums remained conscious until 1 h before death, implying that they were able to experience pain and distress from the effects of ingestion of phosphorus for almost the entire period of illness, which lasted for approximately one day.

Animal welfare and ethical issues relevant to the humane control of vertebrate pests

Vertebrate pests and pest control impact on people, animals and the environment, so any ethical consideration of vertebrate pest control must incorporate the interests of all three. The necessity of intervention, whether it involves killing animals or not, must be properly evaluated. Justification for pest control is only tenable if all of the negative impacts (harms) on people, animals and the environment are minimised and all of the positive impacts (benefits) are maximised as far as can be feasibly achieved. In all cases, the most humane control methods possible must be used; we must actively seek ways to improve the humaneness of existing methods and to find new methods that are more humane. There are six major principles that guide the design and execution of ethically sound vertebrate pest control programmes. (1) The aims or benefits and the harms of each control programme must be clear. (2) Control must only be undertaken if the aims can be achieved. (3) The methods that most effectively achieve the aims of the control programme must be used. (4) The methods must be applied in the best possible way. (5) Whether or not each control programme actually achieved its precise aim must be assessed. (6) Once the desired aims or benefits have been achieved, steps must be taken to maintain the beneficial state. An ideal pest control method would be effective and easy to use, affordable, safe for human users and for people exposed to it, humane, specific to the target species or individuals, and safe for the environment. Although such a gold standard is difficult to achieve, we can only retain ethical credibility if we conscientiously strive to make incremental improvements towards that gold standard.

Using science to support ethical decisions promoting humane livestock slaughter and vertebrate pest control

Ethical principles guide decisions about what we consider to be right or wrong proposals and actions, so that when value judgements are made these engage us in ethics. Ethical thinking is clearly relevant to decisions about the way we treat animals, and such thinking has led to the commonly held view that animal use by people is acceptable provided that such use is humane. The ethical requirement that we treat animals humanely means that we must minimise the harms we do to all animals in our care or under our control. Accordingly, we must assess what harms are done to the animals, how bad each harm is in terms of its intensity and duration, what methods are available or can be developed to minimise each harm, and the relative effectiveness of those methods of harm minimisation. We must also seek to use the most humane methods currently available that can be practically applied. Ethically driven scientific evaluations of this sort have improved the humaneness of livestock slaughter and vertebrate pest control. For instance, detailed studies of different pre-slaughter stunning methods have validated their use to pre-empt the pain and distress that otherwise conscious animals would experience during the fatal neck cut and the short period of consciousness (sensibility) that follows it Likewise, reducing injuries caused by restraint traps has improved the humaneness of this vertebrate pest control method, and comparing the effects of different poisons has allowed the least humane ones to be identified. Difficult questions nevertheless remain at the problematic interface between quantitative scientific observations and their interpretation regarding the suffering that animals may experience, as well as questions about the relativities of different types of suffering.

The Humaneness of Rodent Pest Control

Rat and mouse control methods potentially affect the welfare of many millions of animals every year. Here, the humaneness of the methods used in the UK and the USA is assessed in terms of their speed and mode of action, the appearance and behaviour of affected animals, experiences of human victims, long-term effects on animals that survive exposure, and welfare risks to non-target animals. Several methods emerge as relatively humane: cyanide, alpha-chloralose, electrocution traps and well-designed snap traps all usually kill swiftly and with little distress. Preventative methods such as rodent-proofing are also humane, as well as an essential — and probably under-used — component of effective control. However, anticoagulant poisons, the most common means of controlling rodents, generally take several days to kill, during which time they cause distress, disability and/or pain. Sub-lethally affected animals are also likely to experience haemorrhages and their sequelae, and carnivores feeding on affected rodents may be secondarily poisoned. The acute rodenticides zinc phosphide and calciferol are also generally inhumane, the former typically causing severe pain for several hours, and the latter, pain and illness for several days. Sticky boards, to which rodents become adhered by the feet and fur until they are killed or simply eventually die, also raise very serious welfare concerns. This evidence highlights remarkable paradoxes in the way society treats different classes of animal, and argues for more education, legislation and research targeted at reducing the vast numbers of rodents currently killed inhumanely.

Poisoning with 3-nitropropionic acid in possums (Trichosurus vulpecula)

AIMS

To evaluate the toxicity, animal behavioural effects and animal welfare implications of 3-nitropropionic acid administration in possums.

METHODS

The behavioural effects following 3-nitropropionic acid administration were recorded in 26 possums.

RESULTS

The oral LD50 was between 110 and 170 mg/kg. Time to death averaged 9.5+/-1.9 h (mean+/-s.e.m.). Adverse signs from an animal welfare perspective were retching and restless behaviour that occurred in episodes during a period that averaged 1 h 51 min. Retching occurred in possums that were injected intraperitoneally or dosed orally with the 3-nitropropionic acid, suggesting that this effect was not necessarily initiated by gastric irritation.

CONCLUSION

The potency of 3-nitropropionic acid as a toxin was low compared to other toxins that are used in possums, but it is relatively quick acting. It may cause some discomfort (retching and restlessness) prior to death.