Development of a low-dose warfarin bait for controlling feral hogs

Abstract

Feral hogs inflict an estimated $1.5 billion in agricultural damage in the U.S. each year. Traditional means of control, such as trapping and hunting, have minimal impact on expanding hog populations. Development of a warfarin-based toxicant to control feral hogs began in earnest in 2008 and culminated with an Environment Protection Agency product registration in 2017. Two compounds, warfarin and diphacinone were screened in 2008 as potential candidate toxicants for a feral hog bait to discern a dose level that induced mortality in hogs but would minimize potential non-target wildlife and domestic animal exposure. Test results determined a 0.005% warfarin-formulated bait was efficacious at reducing hog numbers, posing minimal environmental and non-target species risks. Pen studies conducted in 2015 to validate the 2008 findings and utilized a 0.01% warfarin bait. Bait exposure to hogs resulted in all 16 treatment animals expiring from test substance consumption within a 10-day exposure period. Bait consumption averaged 3.98 ± 0.82 kg for the 5-day exposure period. Warfarin residues averaged 2.81 ± 2.07 and 0.88 ± 0.85 μg/g in liver and muscle tissues, respectively. An additional pen study performed in 2015 compared paraffin and corn formulations for palatability and color intensity in internal fat from the fat-soluble blue dye incorporated in the baits. The corn bait was more palatable by hogs, as mean individual consumption was 522.2 and 3,215.5 g for the paraffin and cracked corn bait, respectively. We evaluated the degree of coloration in the internal fat of feral hogs that consumed the toxic bait. The dye concentration was 0.125% of the primary formulation. Corn bait containing 0.005% warfarin, but with half quantity of the blue dye, displayed effective coloration on day 5 of the postexposure period. We concluded that a feral hog bait containing 0.005% was sufficient to ensure mortality and significantly reduce non-target wildlife exposure based on the resulting efficacy and tissue residue levels.