Foam-based depopulation methods of swine differ from water submersion based on computed tomography findings and postmortem lesions.

Abstract

Objective: To investigate the extent of fluid incursion throughout the respiratory tract of anesthetized pigs terminated using 3 different depopulation methods compared to termination by water submersion (H2O).

Methods: Inclusion criteria included pigs aged approximately 40 days. The study occurred over 2 consecutive days during spring. Pigs were anesthetized and terminated using their assigned method: water-based foam, high-expansion nitrogen foam, carbon dioxide gas, or H2O. Respiratory tracts were evaluated 3 ways: CT, gross examination, and histopathology. Immediately after death, pigs were CT scanned, and opacity changes were scored. After gross examination, representative tissues were scored microscopically.

Results: 48 pigs were assigned to 4 treatment groups of 12 pigs each. Compared to all other methods, H2O had higher odds of increased opacities on CT in several proximal structures and bronchi and pulmonary parenchyma of multiple lung lobes. All groups had pulmonary petechiae to regional hemorrhages and subpleural hemorrhages. Emphysema aquosum was observed exclusively in H2O pigs (4 of 12 [33.3%]). Histologically, carbon dioxide gas had 97.8% decreased odds of pulmonary hemorrhage compared to H2O after accounting for sex.

Conclusions: Postmortem lesions and CT opacity patterns associated with water-based foam and high-expansion nitrogen foam are dissimilar to H2O. Foam-based methods involve mechanistic differences from drowning through either environmental or occlusional anoxia, not overt fluid inundation of airways.

Clinical relevance: Foam-based methods are valuable candidates for US swine production and must be separated from the mislabel of drowning. Our findings provide new information regarding large-scale depopulation tools for emergency response efforts.