Letter: Science does not support ventilation shutdown plus

Veterinarians want AVMA's attention on controversial depopulation method

March 1, 2023 (published)

Karen L. Campbell, Amos Deinard, Madeline Graham,
Robin Hadley, Gail R. Hansen, Crystal Heath,
Barbara Hodges, Paula Kislak, Susan Krebsbach,
Peter Mangravite, Ranaella Steinberg,
Debra Teachout & Carrie Waters

Thank you for publishing the VIN News Service article Veterinarians clash over method of mass culling livestock (Feb. 2). It covered how the American Veterinary Medical Association did not permit members who object to the group's stance on ventilation shutdown plus (VSD+) to attend the Humane Endings Symposium, held in late January in Chicago. 

We were pleased that VIN News has helped draw attention to the fact that in 2022, tens of millions of birds were killed with VSD plus heat, a fact about which too few in the veterinary profession are aware. However, there were some issues in the article that we would like to address. For one, it is important to note that all research published or posted publicly shows that VSD plus heat causes death by heatstroke/hyperthermia, rather than low oxygen levels or high carbon dioxide levels. This research is reviewed in "The Rise of Heatstroke as a Method of Depopulating Pigs and Poultry: Implications for the U.S. Veterinary Profession," a commentary published in December in the journal Animals

The VIN News article explains that the U.S. Department of Agriculture expects an infected farm to cull exposed flocks within 24 to 48 hours, and that this allows for few options. However, the claim that VSD can be used to depopulate very large farms within 48 hours is false. Even with the use of VSD plus heat, very few of the big egg production facilities (500,000 or more hens on one premise) are meeting the deadline of culling exposed flocks within 48 hours of presumptive diagnosis (see Table 1 in the commentary and this more recent analysis). If we really want to be able to depopulate within 48 hours, we need to encourage timely deployment of other depopulation methods that work faster than VSD plus heat, such as whole house gassing. If depopulation within 48 hours is necessary to protect human and animal health, we should recommend setting a cap on the maximum number of birds and/or sheds per premise, so that compliance with the USDA's depopulation timeline is feasible.

Highly pathogenic avian influenza (HPAI) may become endemic in wild birds in North America, if it isn't already, according to industry and scientific publications. Last year, more than 44 million laying hens in the U.S. died from depopulation or infection due to HPAI, judging from USDA data. Yet companies developing more humane methods of depopulation, such as high-expansion nitrogen-infused foam, report difficulties securing funding for research. If the AVMA were to reclassify VSD plus heat as "not recommended," using heatstroke to depopulate would disqualify poultry owners from receiving federal indemnity compensation, and the industry would have a financial incentive to invest in advancing more humane depopulation methods.

Another important issue relates to the process by which VSD alone or VSD plus heat or carbon dioxide came to be incorporated in the AVMA Guidelines for the Depopulation of Animals, published in 2019. While Dr. Gail Golab says the AVMA "is guided by science and data," this does not appear to always be the case. The sole report cited to support the classification of VSD plus as "permitted in constrained circumstances" was not peer-reviewed, and the research it describes was not performed under commercial conditions. The research, conducted in 2017 at North Carolina State University, involved individual birds or a very small number of birds housed in a multilevel, full stair-step conventional cage system placed in a 29½-foot-by-15-foot room. 

This report was not publicly available during the open comment period that led to the AVMA depopulation guidelines; only the AVMA Panel on Depopulation had access to it. When the report was made public, a review by the Animal Welfare Institute found numerous shortcomings and errors, which it described in a letter to the AVMA. An article on the research published in the Journal of Applied Poultry Research in December 2018 did not evaluate animal welfare implications.

On the other hand, a large body of literature from the United Kingdom and Europe on depopulation methods and animal welfare at the time of killing failed to be reviewed by AVMA's panel, or at least, was not cited in the guidelines references. If the AVMA truly is to be guided by science and data, it needs to do much better.

Finally, we take issue with the idea that the Humane Endings Symposium could not be conducted in a "respectful and constructive manner" if veterinarians opposed to using heatstroke for depopulation were permitted to attend. The authors of the December commentary published in Animals, and another published by VIN News in January 2022, have shown concern for those people tasked with depopulation and the potential mental health consequences they may suffer. Those consequences are further reasons why our profession as a whole should strive to decrease the need for depopulations.

We should ensure that depopulations are carried out as humanely as possible, in part so they cause less psychological distress to people. Surely, including "kill one's patients with heatstroke" in veterinary job descriptions is something we all can agree would be better left in the past, rather than become business as usual.

Karen L. Campbell, DVM, DACVIM, is based in New Hampshire. Amos Deinard, DVM, PhD, practices in Minnesota. Madeline Graham, DVM, is retired and lives in California. Robin Hadley, DVM, practices in Illinois. Gail R. Hansen, DVM, MPH, is a consultant in Washington D.C. Crystal Heath, DVM, practices in California. Barbara Hodges, DVM, MBA, is a legislative advocate based in California. Paula Kislak, DVM, is a lobbyist based in California. Susan Krebsbach, DVM, is an animal behavior consultant based in Wisconsin. Peter Mangravite, DVM, practices in California. Ranaella Steinberg, DVM, heads the Kauai Society for the Prevention of Cruelty to Animals in Hawaii. Debra Teachout, DVM, MVSc, is a consultant and editor in Illinois. Carrie Waters, DVM, PhD, DACVIM, practices in Maryland.

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