Investigation of alternative baits for rabbit control, and the examination of the distribution and longevity of 1080 in One-shot oats

Abstract

The use of 1080-poisoned oats in rabbit-control programs has become less effective in some areas of Australia. Consequently, factors likely to influence the effectiveness of this bait, and alternative grain products for rabbit control, were investigated. Vacuum impregnation rates with 1080 (sodium monofluoroacetate) for malted and unmalted barley were such that all barley products tested could be used as bait material in conventional rabbit-control programs where individual grains need to contain ~0.02–0.04 mg of 1080. In contrast, only the impregnation rates for malted barley (3.2 mg per grain) showed sufficient promise that this product could be considered for further development for use in 'One-shot' rabbit-control programs (poison grains nominally need to contain 4.5 mg 1080). Compared with oats, non-toxic malted and unmalted barley were equally acceptable food items to free-ranging rabbits. The addition of salt (NaCl, 0.9%) did not enhance the consumption of bait (oats and malted barley).

1080 was not uniformly distributed throughout the poisoned One-shot oats, with 80% of the active ingredient in the husk, and 20% in the kernel. The size of oat also influenced impregnation rates, with the larger grains containing more 1080. Dehusking of the oats by rabbits (i.e. only the kernel was consumed) occurred in ~84% of cases examined (n = 31 food stations). As little as 6 mm of rainfall resulted in the total loss of detectable amounts of 1080 in One-shot oats collected over 41 days from a standard bait trail laid on sandy soil during summer. The impact of the above on rabbit-control programs could be potentially overcome (partially or wholly) by: the development and inclusion of barley products as bait, the alternation of conventional and One-shot baiting techniques in control programs, the responsible inclusion of a chronic poison (e.g. anticoagulant, pindone) in baiting programs, and ensuring that all poison grains in any bait are of uniform size and contain as close as possible to the nominal amount of active ingredient.