Combining aspirin with cholecalciferol (vitamin D3)--a potential new tool for controlling possum populations.

David R Morgan,Mark P Smith,Jane Arrow,Claire Wade

doi:10.1371/journal.pone.0070683

David R Morgan, Mark P Smith + Show 2 more

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https://doi.org/10.1371/journal.pone.0070683

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Abstract

The introduced Australian brushtail possum is a major vertebrate pest in New Zealand, with impacts on conservation and agriculture being managed largely through poisoning operations. Cholecalciferol (vitamin D3) is registered for use in controlling possums and despite its many advantages it is expensive and relatively inhumane. Combination of a high proportion of aspirin with a low proportion of cholecalciferol was effective in killing high proportions of groups of acclimatised, caged possums: this is attributed to both an unexpectedly high toxicity of the type of cholecalciferol used, and a proposed synergistic mechanism between the two compounds. Death was caused by localised damage to heart ventricles by aspirin, and inhibition of tissue repair by both aspirin and cholecalciferol. The observed toxicosis had lower impact on the welfare of possums than either compound administered alone, particularly aspirin alone. Residue analyses of bait remains in the GI tract suggested a low risk of secondary poisoning by either compound. The combination of cholecalciferol and aspirin has the potential to meet key requirements of cost-effectiveness and humaneness in controlling possum populations, but the effect of the combination in non-target species has yet to be tested.

Highlights

The brushtail possum (Trichosurus vulpecula) is a nocturnal, arboreal, largely herbivorous marsupial about the same size as the domestic cat
The combination of 0.1% cholecalciferol with 20% aspirin that we found in bait consumption trials to be optimal in terms of palatability and effectiveness offers a cost-saving of about 65% compared with the presently-registered lowest concentration of cholecalciferol of 0.4% used in possum baits [28]
Continued progress in eradicating bovine tuberculosis [29] and restoring conservation values [30] in New Zealand is presently underpinned by a strategic approach to the control of invasive vertebrate pests, a major component of which is the use of 1080 poison to control possum populations [31]

Summary

Introduction

The brushtail possum (Trichosurus vulpecula) is a nocturnal, arboreal, largely herbivorous marsupial about the same size as the domestic cat It was introduced over 150 years ago from Australia to New Zealand to establish a fur trade, and has become a major pest, causing extensive damage to conservation values, agricultural crops and forest plantations, and by spreading bovine tuberculosis [1]. Poisoning occurs through absorption of cholecalciferol from the intestine, conversion to 25–hydroxycholecalciferol in the liver, and subsequent conversion in the kidney to 1,25-dihydroxycholecalciferol, the biologically active form of the vitamin [7] The latter metabolite works in conjunction with the parathyroid hormone to release calcium from storage in bone and other tissues and to reabsorb calcium in the kidney [8], leading to a maximum concentration of blood calcium in possums at about 4 days [9]. The blood hypercalcaemia leads to excessive calcification in soft tissues including blood vessels, and death from heart failure in most possums after 4–7 days [9]

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