Ventilation shutdown

The JAVMA recently published a report¹ on the use of ventilation shutdown with high temperature and humidity (VSD+TH) for de-population of 243,016 pigs. While the report suggests its findings could guide future use of this method, my conclusion differs: ventilation shutdown, in any form, entails enormous suffering for the animals involved, and our profession must urgently take measures to ensure it is never used again.

The AVMA Guidelines for the Depopulation of Animals find that, in some circumstances, VSD is acceptable if at least 95% mortality is achieved within an hour.² The recent report confirmed that VSD+TH kills by causing heat-stroke, and having witnessed the suffering of heatstroke patients, I disagree with this standard as a benchmark for moral acceptability.

However, even if we accept it, I question the article's claim that this condition was met. To meet this criterion, time 0 was set, not at the point when ventilation was shut down and heating was initiated, but 15 to 94 minutes later, when the temperature reached a scorching 130 °F and steam was introduced. While the report attempts to justify starting the clock at this point, the pork industry's own standards state that the preferred temperature range for nursery and finishing pigs is 65 to 80 °F and 50 to 75 °F, respectively, and the “upper critical thermal limit” is 95 °F.³ If we start counting when heat began being pumped into the barn, the report indicates that each VSD cycle took an average of 90.4 minutes for nursery pigs and 110.3 minutes for finishing pigs, at times lasting over 2.5 hours. This total time more accurately reflects how long these pigs suffered, failing to meet the standard of “95% mortality rate in < 1 hour.”¹ Moreover, recent literature reviews of depopulation methods conclude that welfare costs of any form of VSD are simply too great for it to be used, even in disease control situations.^4,5

The report explains that electrocution, which causes instantaneous loss of consciousness when properly used, was rejected because a farm-tested system would take too long to develop. However, mobile electrocution units are already contained in the veterinary stockpiles of several European nations and Nebraska. The National Pork Board's recent research on mobile electrocution units for pigs shows the costs, staffing requirements, and application speed are equivalent or superior to those described for VSD+TH.⁶

The AVMA depopulation guidelines require that every effort be taken “to ensure that animals designated for depopulation experience a rapid loss of consciousness or loss of brain function under the prevailing conditions.” Given the findings of the VSD+TH report and the available alternatives, we must regard any future use of VSD as avoidable and morally unacceptable.

I must wonder how future generations will look upon mass killing of healthy animals by heat-stroke. Will American veterinarians be remembered as those who legitimized a method internationally regarded as unacceptable on animal welfare grounds? Or will we be able to say that we used our expertise, resourcefulness, and influence to ensure ventilation shutdown was never used again?

Gwendolen A. Reyes-Illg, DVM, MA

Milwaukie, Oregon

We are writing regarding “A case study of ventilation shutdown with the addition of high temperature and humidity for depopulation of pigs.”¹ The authors provide a good description of the swine industry in the US and the limited flexibility and capacity for responses during emergency situations in the case report.

Veterinarians working in livestock industries are very aware of the pathophysiology of death by heatstroke and the effects on affective states during that process. The swine industry requires ventilation to maintain comfort of animals in enclosed housing. The Pork Quality Assurance Program PQA Plus Version 4 states “facilities must have intervention procedures or equipment to prevent death of animals in the event of mechanical ventilation failure.”²

The AVMA Guidelines for the Depopulation of Animals³ lists 10 assessment criteria regarding de-population methods. Criteria 1 is the “ability to induce loss of consciousness followed by death with a minimum of pain or distress,” 2 is “time required to induce loss of consciousness and the behavior of the animal during that time,” and 3 is “reliability and irreversibility of the methods resulting in death of the animal.”³

A summary of the pathophysiology leading to death by heat-stroke is “When heat gain overwhelms the body's mechanisms of heat loss, the body temperature rises, potentially leading to heat-stroke. Excessive heat denatures proteins, destabilizes phospholipids and lipoproteins, and liquefies membrane lipids, leading to cardiovascular collapse, multiorgan failure, and, ultimately, death.”⁴

Animal welfare is negatively affected before signs of heat stress are demonstrated and is progressively affected with increasing temperature and time of exposure. Table 1 from the report¹ presents data showing the time to signs of severe heat stress (time to 0) for nursery and finishing pigs and the range of time for pigs to become silent. Efficacy (death) was apparently determined by total cycle time, ranging from 110 minutes (nursery pigs) to 151 minutes (finishing pigs). Data from the report demonstrate a lack of conformity with the AVMA depopulation guidelines criteria.

Pigs in this report¹ suffered for considerable lengths of time before becoming quiet and eventually dying. The article accepts that ventilation shutdown is not humane (Figure 2) and highlights a serious need to protect animal welfare in the swine industry when another national emergency occurs. Data in the report are important to the welfare of swine.

We respectfully ask the AVMA to work with the pork industry, the veterinary profession, and government agencies to develop action plans to prevent the need and use for ventilation shutdown for depopulation.

Jim Reynolds, DVM, MPVM, DACAW

Jose Peralta, DVM, PhD, DACAW

Beth Boynton, DVM, FNAP

Western University of Health Sciences

College of Veterinary Medicine

Pomona, California

Author's response:

In the last 18 months, veterinarians have been faced with extreme stress due to unforeseen complications associated with the human COVID-19 pandemic. Specific to the swine veterinary community, many of us were challenged to identify and implement a depopulation method for on-farm use, utilizing the limited resources and personnel available during this challenging time. The case study served as a report of a ventilation shutdown with temperature and humidity (VSD+TH) event that occurred during the height of COVID-19 with the intention to document the method and share the data as a means to improve the knowledge and understanding of VSD+TH use in swine. Additionally, this case report will serve to inform and guide swine veterinarian decision-making for future situations in which depopulation is warranted due to another pandemic or trans-boundary disease introduction.

To provide situational context, the COVID-19 processing plant shutdowns (eg, facility closures ≥ 14 days in duration with 50% to 100% reduction in slaughter capacity) resulted from mandated slaughter facility closures due to the inability to operate because of increased absenteeism of staff infected with COVID-19. As a result, these shutdowns negatively impacted the movement and care of swine housed on associated farms. In addition, plant closures resulted in the need for depopulation as animal density exceeded stocking density requirements and increased aggressive behaviors between pigs due to competition for food, water, and space.

The AVMA depopulation guidelines¹ describe preferred methods and those permitted in constrained circumstances for swine. When this depopulation event occurred, preferred depopulation methods were not available given limited resources (eg, labor, CO₂ gas, and mobile electrocution devices) and human safety concerns. Electrocution via a mobile device had not been developed and validated for depopulation until after the depopulation event described in our paper was concluded.² Similar mobile electrocution units developed by Iowa State University were still in the initial proof-of-concept phase, thus eliminating electrocution as an option for this depopulation event.

Ventilation shutdown plus (VSD+) is a method of depopulation that results in “raising the temperature in the house until animals die from hyperthermia.” In contrast to VSD alone, VSD+ methods implement additional elements such as retrofitted barn design, supplemental heat, and humidity to achieve a higher mortality rate in the shortest time possible. Given that this case report documented VSD+TH, time 0 was defined once all elements (temperature and humidity) of the method were applied. Using this time 0, 99% of mortality was achieved within 60 minutes for this specific method.

To date, there are no peer-reviewed studies on the physiologic response of swine to hyperthermia. However, extrapolating data from nonswine animal studies suggests that the onset of behavioral deviations and CNS impairment, as demonstrated by decreased auditory brain response amplitude, occurs when the core body temperature achieves ≥ 43 °C.^3,4,5 Given logistic constraints of this emergency on-farm event, core body temperature was not recorded for pigs, but the humidity was applied when the barn temperatures reached 54 °C and barns were maintained at a minimum of 49 °C for the duration of the procedure. Therefore, future research using VSD+TH must consider documenting core body temperature and behavior of pigs to quantify the temperature threshold that results in impaired cortical activity.

Implementing VSD+TH was an excruciating decision for many veterinarians involved in the process, and we need to acknowledge how criticism from peers may have unintended negative consequences on our colleagues. We must rally behind those involved, beginning with acknowledging the strain and negative mental health effects experienced by many veterinarians involved with these events. Additionally, as a community, we must provide solutions to identify depopulation challenges when resources are not available to allow implementation of preferred methods.

It is well-known that our profession is in the midst of a mental health crisis.⁶ One in 6 veterinarians in the US has contemplated suicide, and veterinarians are 2.7 times as likely to attempt suicide when compared to the general population. The majority of veterinarians in the US identify as highly stressed and suffer from compassion fatigue and mental burnout. Even more so, veterinarians directly involved in emergency response and disaster planning, such as the depopulation events that occurred in 2020, are at an elevated risk for long-lasting mental health effects. In fact, in our recent work evaluating the emotional impact of swine veterinarians involved in depopulation, we found that 10% of swine veterinarians surveyed have thought about suicide and 23% have reported needing mental health counseling and are not receiving it.

Do not forget the human element of veterinary medicine.⁶ Hindsight is always 20/20, and we need to learn from catastrophic events while supporting our peers. Criticism from friends, family, and colleagues directly impacts the distress level experienced by veterinarians involved in difficult decision-making. The anguish in this decision-making may be compounded when individuals are judged by those who lack understanding. I hope that this case report can be used as a tool to advance depopulation methods for swine in the future, recognizing that human safety and mental health are equally important to the animals' welfare.

Angela Baysinger, DVM, MS DeSoto, Kansas

Michael Senn, DVM, MS

Wichita, Kansas

Jordan Gebhardt, DVM, Phd

Manhattan, Kansas

Christopher Rademacher, DVM

Ames, Iowa

Monique Pairis-Garcia, DVM, PhD

Raleigh, North Carolina

Spectrum of care

Imagine how much greater the effectiveness of the innovative “spectrum of care”¹ approach in veterinary education could be if our profession adopted designated licensing that was congruent with more focused and comprehensive career tracks in the major career branches of veterinary medical education, namely community (general) practice, small animal practice, food animal practice, equine practice, one health, nondomestic animals, and medical research. The sum of the parts would vastly increase our capacity to provide more competent service to society and have the flexibility to adapt to its changing needs while being more rewarding to individual veterinarians.

N. Ole Nielsen, DVM, PhD

Spruce Grove, AB, Canada