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Seeking the Best Method for Mass Depopulation of Broilers

18 February 2009

With the continual threat of avian flu worldwide, there is a clear need to identify the most practical method for the depopulation of poultry houses that results in the minimum suffering of the birds. ThePoultrySite editor, Jackie Linden, reports how scientists from Delaware have discovered that foam is more effective than gassing and that a carbon dioxide foam was more efficient than one based on water.

A confirmed outbreak of H5N1 highly pathogenic avian influenza must be high on every poultry farmer and veterinarian's list of fears. Among the worst aspects is the need to depopulate the farm as quickly and efficiently as possible, taking into account the welfare of the birds, human health, safety and management of the infection outside the house.

Current control strategies for avian influenza and other highly contagious poultry diseases often include quarantine, depopulation and disposal of infected birds. For biosecurity reasons, on-farm depopulation and disposal methods are preferred.

The options for mass depopulation are limited, particularly taking into account labour requirements, applicability for all house types, and suitability for large-scale emergency implementation. A procedure has been developed that uses foam to rapidly form a blanket over the birds. The procedure requires relatively few people, can be performed in a variety of house types, and is compatible with in-house composting.

The USDA's animal health group, Animal and Plant Health Inspection Service (APHIS) recommends the use of gassing rather than a foam as a means of mass suffocating as individual methods of culling are impractical on a farm scale. However, gassing presents some practical difficulties as it requires that the gas is contained within the house. Even with a new and airtight building, this may require the use of a plastic sheet to cover the birds and contain the gas.

New Research from Delaware

A group of researchers from the University of Delaware reported their recent work into the best options for mass depopulation of broiler houses in two papers presented at the International Poultry Scientific Forum in Atlanta, Georgia, USA, last month.

In his introduction, Dr Keith Johnson explained that the preferred method for mass depopulation currently is gassing - either a full house, partial house or in a container. As an alternative, foam may be used, using with carbon dioxide or ambient air. Carbon dioxide gassing is the currently used method in the US and internationally for mass depopulation. It works by inducing chemical hypoxia (suffocation). It has the advantages that supplied and equipment are easily available. However, it has the disadvantages that it is difficult to establish the proper kill concentration, it has a freezing effect, can be hazardous to humans and is labour-intensive.

Dr Johnson explained that a mixture of carbon dioxide and argon is thought to be more humane. Argon displaces oxygen. The disadvantages, he said, are that it requires a high concentration to be effective, it poses some human health hazards and it requires rigid control of the gas concentration.

The use of water-based foam was conditionally approved by APHIS is 2006. The foam form a blanket to block air, causing a physical hypoxia (suffocation). It requires less labour but is requires specialist equipment and uses large amounts of water.

Foam versus Gassing

In the first paper from the University of Delaware, Dr Johnson compared the responses of broilers during depopulation using a water-based foam or gassing with carbon dioxide alone, or as a mixture with argon (70 per cent argon to 30 per cent carbon dioxide).

He explained that the research was conducted to measure the differences in physiological responses of broiler chickens using three methods of emergency mass population.

Physiological responses to each of the three methods were quantified using an electrocardiogram (ECG; to measure heart rate), electroencephalogram (EEG; to measure brain activity) and motion-sensing equipment bound to one of the bird's legs.

Each broiler was place individually into a treatment chamber and exposed to a single depopulation method. Physiological responses and motion of the birds were monitored and recorded for up to 15 minutes.

The average times to motion cessation were 122, 189 and 120 seconds, for carbon dioxide, argon-carbon dioxide and foam, respectively. The foam gave by far the most consistent response. By 180 seconds (three minutes), all of the birds depopulated using the foam had ceased motion, whereas the gases took seven minutes to kill all the birds.

The mean times to EEG silence were 128, 204 and 140 seconds, respectively and again, the responses to foam were the most consistent. All the birds in the foam had died within four minutes. It took seven minutes for the birds n carbon dioxide to die, and eight minutes for those in the argon-carbon dioxide mixture.

Dr Johnson summarised his results by saying that argon-carbon dioxide mixture offered no advantages, and took the longest time to be effective and was the least consistent. The results for carbon dioxide were similar to foam but less consistent. As the scale is increased, consistency issues are likely to be magnified, he warned.

Comparing Different Types of Foam

Mary Rankin reported in her paper the group's work to compare water-based and carbon dioxide foam during depopulation of a broiler house.

She used the same methods as before to compare the birds responses, and found that both materials gave similar results based on the data from the EEG and motion sensors.

EEG silence using the water-based foam occurred within 140 seconds and in 190 seconds for the carbon dioxide foam. Average times for motion to cease were 120 seconds and 100 seconds, respectively.

Dr Rankin concluded that the two methods produced very similar results in her trials. Using carbon dioxide is more expensive in terms of time, labour and equipment required to achieve the required level of carbon dioxide (above 5000 ppm).

So from this work at the University of Delaware on a relatively small sample of broilers, it appears that using a carbon dioxide foam induces unconsciousness and death more quickly than the officially preferred method of gassing.

Foam also offer a number of additional practical advantages in that it rapidly forms a blanket over the birds, requires relatively few people, can be performed in a variety of house types, and is compatible with in-house composting.

Further Reading

- You can view Use of Water-Based Foam for Depopulation of Poultry from the American Veterinary Medical Association by clicking here.



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