Microencapsulated sodium nitrite is a humane solution for domestic grower pig depopulation during an emergency animal disease response.

Abstract

Methods of domestic pig destruction that require individual handling cause distress, carry a risk of ineffective or painful stunning or wounding, and pose physical and psychosocial safety risks to operators. Oral intoxication of pigs via feed offers an alternative approach that reduces these risks. An experiment was conducted to validate the oral administration of microencapsulated sodium nitrite (meSN) to group-housed domestic grower pigs and assess the suitability of meSN as a mass destruction method for application during an emergency animal disease (EAD) response. Twenty-four individually identified pigs were administered a pre-feeding regimen followed by delivery of 10% (w/w) meSN paste (Treatment 1) or 100% meSN as a top-dress on standard pig feed (Treatment 2). Pigs ingested both treatments and presented with no visual signs of distress and demonstrated post-feeding and exploratory behaviors consistent with those of group-housed pigs for 20-40 min after consumption of the toxic substrate. Intoxication presented as a visible reduction in movement/activity followed by recumbency, dullness, loss of responsiveness, and eventually death. All treated pigs died. The welfare compromise requiring intervention was not observed by the attending veterinarians. Our findings suggest that after meSN application, pigs may be safely moved for about 15 min when using paste or for about 30 min when using top-dress granules. After this time, pigs will start to lose posture and will have difficulty standing or walking. No clinically significant gross or histological post-mortem tissue changes were detected. Tissue and intestinal content residues indicated that the risk of secondary nitrite/nitrate poisoning to carcass scavengers is negligible. Critical contributors to successful lethal outcomes are considered to include: sodium nitrite stability and palatability offered by microencapsulation; successful transition to a placebo paste before application if a paste formulation is used; consumption of a lethal dose that accounts for wastage and uneven consumption by pigs sharing feed; and consumption being sufficiently rapid to overwhelm toxin metabolism pathways and cause death.