What do I need to know about drug withholding periods for my chickens?

The Australian Pesticides and Veterinary Medicine Authority (APVMA) has defined food-producing animal species as any animal used to produce food for human consumption, or which is used as food for human beings, and includes any buffalo, cattle, deer, fish (other than ornamental fish), goat, kangaroo, pig, poultry, rabbit, sheep, bee, crustacean or mollusc.

There are restrictions placed on the use of medications in all food-producing species, including backyard poultry, to prevent residues of drugs appearing in our food. These residues could trigger allergic reactions or other problems in some people, but the biggest concern is that bacteria exposed to low levels of antibiotics in food will develop resistance against that antibiotic. This could lead to a world where antibiotics are no longer effective in treating infections.

A withholding period is the length of time needed after treatment is finished to ensure that meat or eggs produced by the birds do not contain illegal residues; i.e., the minimum period that must elapse between the last use of a product in relation to an animal and the slaughter of the animal, or the collection of eggs from the animal for human consumption to ensure that the product’s residues fall to, or below, the Australian-defined minimum residue levels. (Note that this does NOT mean “store the eggs in the fridge and consume after expiration of the withholding period.”)

Ideally, only drugs registered for chickens (with a known withholding period) should be used. Technically, however, this means that there are few drugs that can be used in backyard poultry. A commonsense approach to this problem has been adopted by many avian vets, using the following guidelines:

1. Medications for poultry must be prescribed by a registered veterinarian for a bona fide client, having established a therapeutic need based on current knowledge of the health of the animals to be treated. This means that, just like our own medicines must be prescribed by our doctor, the drug for your chickens must be prescribed by a vet that has seen your chickens and determined the drugs are needed. You cannot just buy drugs over the counter after getting advice from someone else.
2. Drugs that are banned in all food-producing species cannot be used in poultry of any type at any time. Several antibiotics come into this category.
3. Drugs that are registered in poultry can be used with the withholding period provided by the manufacturer.
4. There are drugs that are registered in other food-producing species but not in chickens. These drugs can be used, with a withholding period as used in other species.
5. Those drugs that are not registered in poultry, but are similar to those that are registered, can be used with the withholding period the registered drug.
6. Those drugs that are not registered in any food-producing species, but not banned can be used with a withholding period of 4-6 weeks.