Characterizing the Distribution of Water-Based Foam and High-Expansion Nitrogen Foam Within the Swine Respiratory Tract Using Computed Tomography

Abstract

Pigs in the United States are at risk of contracting diseases of economic and zoonotic importance, with outbreak situations requiring immediate mass depopulation for disease control. Swine depopulation methods currently approved by the American Veterinary Medical Association (AVMA) have concerning limitations, such as significant animal aversiveness, biohazardous exposures, or low practicality of implementation in field situations or large volumes. Therefore, there is an urgent need for depopulation methods that are replicable and reliable in emergent situations while being mindful of animal welfare. Two emerging foam-based methodologies include water-based foam (WBF) and high-expansion nitrogen foam (N₂F). Water-based foam is a cost-effective, accessible, and rapid method of swine depopulation across all ages of swine, with repeated large-scale success. Likewise, N₂F has demonstrated potential utility in swine depopulation with results in rapid times to loss of consciousness and animal death.

Currently, the AVMA is reviewing new and alternative options for animal depopulation methods. The addition of foam-based depopulation methods would allow producers to soon equip themselves with additional depopulation strategies should outbreak events occur. While there has been repeated success in foam-based swine depopulation, the effects these methods have on the swine respiratory system have not been investigated, and the distribution and movement of foams along the swine respiratory tract remain poorly understood. We need to generate concrete evidence for the understanding of foam-based mechanisms in animals, gauged along the spectrum between death due to pure water submersion (“drowning”) and gas inhalation (ex., CO₂). There are no previous studies describing the extent of foam infiltration in pigs that utilize methods that eliminate movement of the animal after death, which otherwise risk compromising the accuracy of study results. Considering that foam generation combines liquid concentrate-water mix and gas, a detailed investigation of foam penetration within the respiratory tract of pigs using computed tomography (CT) provides data is needed.

In any event of disease outbreaks, providing timely depopulation of animals will be key to disease containment. Expanding our understanding of WBF and nitrogen foams by characterizing their distribution within the swine respiratory tract will provide the final, critical piece to AVMA and accelerate decision making on its utility. The end goal is to provide pork producers with more cost-effective, accessible, and easily deployable depopulation strategies to combat any emergency situations affecting U.S. swine herds.