What are the animal welfare issues with mass killing using ventilation shutdown?

Ventilation shutdown involves sealing a shed by shutting air inlets and/or by turning off ventilation fans following which the internal shed temperature rises from animals’ body heat and toxic gases accumulate from a build-up of manure in the shed. The high temperature in combination with the toxic gases is maintained for several hours to days and ultimately kills the animals in the shed by hyperthermia (extreme heat) and hypoxia (suffocation) [1]. Ventilation shutdown is considered an inhumane method of killing because it causes prolonged distress and suffering to animals before death.

Why is mass killing of farm animals required?

Mass killing, or the humane killing of large numbers of farm animals, is at times required in the event of an emergency animal disease outbreak to control and prevent further spread of the disease.

In this context, ventilation shutdown has been previously used as a method to kill large numbers of poultry or pigs during emergency animal disease outbreaks. In countries such as the United States and UK, the use of ventilation shutdown has been used as a method of mass killing of poultry during outbreak of highly pathogenic avian influenza, and in pigs due to transport restrictions from the COVID-19 pandemic.

What are the animal welfare issues with ventilation shutdown?

Ventilation shutdown causes prolonged distress and suffering of animals before death. The effectiveness and time to death is variable depending on a number a factors, including the shed type, age and size of animals, the number of animals, the type of ventilation system, the ability to seal shed air inlets and environmental conditions like outside temperatures.

Ventilation shutdown may also have supplemental heat and/or humidity added during the process to speed up the time to death. Time to death in poultry using the various forms of ventilation shutdown can vary from 1.5 to nearly 4 hours [2]. Similarly, time to death in pigs using ventilation shutdown with high temperatures has been shown to take multiple hours [3]. Some forms of ventilation shutdown have also been shown to not always be effective at killing all the animals inside a shed [4].

During ventilation shutdown animals are subjected to excessive heat and toxic gases for a prolonged and often unpredictable period before losing consciousness. The prolonged time to loss of consciousness and unpredictability is unacceptable when compared to other depopulation methods, such as carbon dioxide gas or high expansion foam (see below), in which unconsciousness and death can be achieved in minutes.

The current Australian Veterinary Emergency Plan for destruction of animals (AUSVETPLAN Edition 3.2) states that ventilation shutdown is an unacceptable method to depopulate birds given the animal welfare concerns and lack of scientific evidence around its effectiveness [5].

What are the alternatives of ventilation shutdown?

There are a number of more humane methods of mass killing for pigs and poultry available that have also been used during various outbreaks of emergency animal diseases. When mass killing is required, there are numerous factors that must be taken into consideration to determine the most appropriate method given the specific situation.

For poultry, the alternative mass killing methods include carbon dioxide gas and/or inert gases, foam, low atmospheric pressure, or captive bolt devices. For pigs the alternative mass killing methods include carbon dioxide gas and/or inert gases, captive bolt devices, or firearms. To read more about animal welfare considerations during mass killing, click here.

The RSPCA is of the view that more research and funding is needed to develop and commercialise more humane, effective, and practical methods of mass killing to ensure that Australia is prepared in the event of an emergency animal disease outbreak.

What is the RSPCA’s view on ventilation shutdown?

The RSPCA defines humane killing as when an animal is either killed instantly or rendered insensible until death ensues, without pain, suffering or distress. The RSPCA is opposed to the use of any form of ventilation shutdown for mass killing because it results in animals experiencing prolonged periods of pain, suffering, and distress before death.