Letter: Guiding animal depopulation is complex, daunting

AVMA stance on VSD plus could evolve as efforts to curb avian flu unfold

March 13, 2023 (published)
From Janet Donlin, Gail Golab & Lori Teller

As veterinarians, we are dedicated to the protection of animals' health and welfare and the prevention and relief of animal suffering, and we have public health responsibilities, as well. Accordingly, there are times when we must provide guidance on when and how to end animals' lives. This responsibility is particularly difficult when disease or other catastrophic events affect very large numbers of animals.

Unfortunately, the reality is that there have been and will most assuredly continue to be situations that make the depopulation of animals necessary. We share the animal welfare concerns of the authors of the letter Science does not support ventilation shutdown plus (March 1). Therefore, we believe that such serious, complicated and evolving challenges to animal health require both compassion and expert scientific analysis. It is why, on behalf of the profession, the American Veterinary Medical Association embarked on the important, difficult and emotionally taxing construction of depopulation guidance. 

Evaluating and developing recommendations regarding methods of depopulation is embedded within a daunting list of considerations to be addressed: animal welfare; disease control; human safety; federal, state and local regulations; resource availability; feasibility; environmental protection; economics; and the mental and emotional impact on those who conduct and manage depopulation events. When depopulation is necessary, the methods selected for any given situation will always have trade-offs among these considerations and often don't come with better alternatives.

Recognizing that veterinarians who are involved in these decisions need guidance that is focused on ensuring depopulation is carried out as humanely as possible, the AVMA spent more than two years developing the first edition of its Guidelines for the Depopulation of Animals, which was published in 2019. More than 70 subject-matter experts, including a credentialed ethicist, contributed. These guidelines, like their euthanasia and slaughter counterparts, are recognized nationally and internationally for their quality of content, the thoughtful process used to construct them, and the deliberate attention paid to ensuring they are ethically sound. 

Because the situations that lead to depopulation are typically complex and often not fully possible to replicate in research, we unfortunately end up gathering key information about the practical implementation and impacts of these methods when they are carried out under actual emergency conditions. In developing the 2019 guidelines, our panel members were able to draw on what was learned from responding to previous disasters, including the 2015 outbreak of highly pathogenic avian influenza (HPAI), during which water-based foam (preferred method), CO2 (preferred method) and VSD (not recommended method) were all used. Challenges were noted with the use of each method, including that the use of water-based foam can be limited by insufficient quantities of water to make the foam, as well as the temperature and type of housing; that whole-house gassing is limited by sourcing CO2 and the ability to seal the facility sufficiently to prevent gas from escaping; and that VSD was a new method with limited knowledge about its use, effects and how to improve it.

Because of the ongoing HPAI outbreak, we now have a great deal more information about what did and did not work well when deploying VSD+ (permitted in constrained circumstances) at scale, and we will use these data to help refine recommendations in our guidelines moving forward.

Nitrogen-infused foam for depopulation currently is being developed and evaluated and, in fact, various approaches were presented and discussed at the recent AVMA Humane Endings Symposium. However, it has not yet been fully tested in production facilities of the various types and sizes commonly encountered in the United States.

While there are challenges in constructing representative trials, peer-reviewed research also is critical to the evaluation of these methods and the development of the guidelines. Members of the Panel on Depopulation and its working groups continuously scour the scientific literature; have leveraged the work of authors from all over the world, including three prominent poultry scientists in Europe; and obtain access to pre-publication copies of manuscripts and proprietary data, such as the 2018 paper Evaluation of Ventilation Shutdown in a Multi-level Caged System. 

As we write, almost 59 million birds across 47 states have been infected with HPAI, and the U.S. Department of Agriculture has compiled a list of 14 species of mammals that have contracted the disease. Faced with such alarming situations, we are all committed to finding better solutions. The AVMA continually collects and reviews information, and we update the guidelines as new scientific data are published and/or verifiable proprietary data are shared. A considerable amount of new scientific data is coming in, and we are in the process of reviewing all methods of depopulation, not just VSD or VSD+, as we work to create the next edition of the Guidelines on Depopulation.

To support this process, the AVMA's humane endings symposia offer a forum for top experts on the subjects of euthanasia, humane slaughter and depopulation to gather, share information, have open and thoughtful discussions, and hear directly from scientists that have, or will, publish critical information on these topics. Attendees also hold a range of views and perspectives, so it is imperative that we provide a mentally and physically safe environment where these discussions can take place without fear of verbal or physical attack, misrepresentation of their comments and public reprisal. Unfortunately, some have chosen to be disruptive in the way they express their views, and such behavior unfortunately forced us to limit attendance at this year's event.

The AVMA recognizes that animal health and welfare as well as public health and safety are critically important pieces of the decision-making process when it comes to ending the lives of animals. We look forward to seeing improved methods and techniques developed for the exigent circumstances under which depopulation occurs, and remain committed to providing veterinarians with the guidance they desperately need when depopulation is deemed necessary.

Janet D. Donlin, DVM, CAE, is executive vice president and chief executive officer of the American Veterinary Medical Association. Gail Golab, PhD, DVM, MANZCVS, DACAW, is associate executive vice president and chief veterinary officer of the AVMA. Lori Teller, DVM, is AVMA president and a clinical associate professor of telehealth at the Texas A&M College of Veterinary Medicine & Biomedical Sciences.

Editor's note: The last five paragraphs of the letter were inadvertently omitted from the original submission; the missing section has been added, post-publication.

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