Spread of infectious disease to a broiler farm ranks right up there with destruction of poultry houses by wind, fire or flood on the list of a grower’s worst nightmares.

The possible spread of the Asian strain of highly pathogenic avian influenza (HPAI) to the U.S. has ratcheted up the concern over the damage that disease can cause to the poultry industry. One of the tools used to contain an outbreak of infectious disease is depopulation of the affected farms, and, in many cases, depopulation of farms within a certain proximity, or quarantine zone, of the affected farms. The standard means of euthanizing broilers, turkeys and layers in the U.S. has been with carbon dioxide, but water-based foam may replace carbon dioxide in the future.

Carbon dioxide is heavier than air and is toxic to animals and humans in high concentrations, but it has some disadvantages as a euthanizing agent. Using carbon dioxide to euthanize birds requires a crew of people to use rolls of plastic to form a “tent” over the birds to confine the carbon dioxide and keep it from diffusing throughout the air space in the house.

Making the tent reduces both the amount of carbon dioxide needed and the time required to euthanize a house of birds. However, the crew required to euthanize a flock with carbon dioxide risks exposure to both the carbon dioxide in high concentrations and to the infectious agent on the farm. The more people brought on to a farm the greater the risk that the disease agent will be tracked back off the farm.

Last fall, the American Veterinary Medical Association and the USDA’s Animal and Plant Health Inspection Service both gave approval to the use of water-based foam as a method of mass depopulation for poultry. The foam used is similar to fire fighting foam which is used to smother a fire. When used for euthanasia, the bubbles in the foam block the trachea of the bird and rapidly cause hypoxia, which is a reduction of oxygen in the body that leads to death. A high carbon dioxide level in the air also causes death by hypoxia.

Research at the University of Delaware has shown that medium-expansion foam with small bubbles works best for inducing hypoxia in birds. A single individual, using a commercially available foamer, developed specifically for this purpose, can fill a typical broiler house to a depth of three to four feet of foam in around a half hour. In a disease outbreak, it may be necessary to put down flocks on several farms in a period of 24 to 48 hours.

Foam depopulation offers the poultry industry a tool which may make rapid depopulation possible, and it may help stop the spread of a disease like avian influenza, whether it is HPAI or low-path AI.