Efficacy of encapsulated sodium nitrite as a new tool for feral pig management

Abstract

Worldwide feral pigs threaten native biodiversity, agricultural production and pose a risk to biosecurity as potential disease vectors. In New Zealand, the management of feral pigs has long been restricted to hunting, trapping, fencing and limited poisoning with 1080, warfarin and phosphorus. Sodium nitrite (NaNO2) is commonly used at very low concentrations in the food industry. At high doses, NaNO2 induces methaemoglobinaemia in mammals restricting the transport of oxygen by the red blood cell and in toxic doses leads to central nervous system anoxia, lethargy and death. Pen and field trials with pigs have been undertaken with an encapsulated formulation of NaNO2, designed to overcome the bitter taste of NaNO2 and mixed into a palatable paste bait. In pen trials, eight out of nine pigs consumed a lethal dose of paste bait. The average time to death was 59.5 min (±23.96 SD); symptoms lasted an average of 42.13 min (±19.12 SD) and included pale extremities, lethargy and ataxia. In a field trial, 12 radio-collared feral pigs were baited with the toxic paste bait formulation in prototype bait stations, where 11 of the 12 pigs consumed a lethal dose. Encapsulated NaNO2 has potential as an additional tool for the management of feral pigs, particularly when shooting and hunting is not practical or possible. Data in these studies were used to register this bait as a vertebrate toxic agent for feral pig management in New Zealand. This represents the first known registration of NaNO2 worldwide for use as a vertebrate toxic agent.