http://www.soilassociation.org/whatisorganic/organicanimals/poultry
Soil Association : Poultry

Poultry

Organic chickens and turkeys are able to behave naturally - grazing, pecking the ground, scratching and dust-bathing. Organic poultry must have continuous and easy daytime access to pasture or range covered with suitable vegetation, except in adverse weather conditions. Organic poultry cannot be permanently housed, though shelter and protection from predators must be provided at all times.

Pasture must be regularly rested from poultry to allow vegetation to recover and prevent the build up of parasites. Chickens being raised for meat (broilers) must be housed with room for a maximum of 10 birds per square metre. A flock must not contain more than 1,000 birds. (Intensively-reared broiler chickens are normally housed in groups of up to 40,000 in large shed.) For chickens raised to lay eggs, Soil Association organic rules do not allow more than six birds per square metre indoors, with a maximum flock size of 2,000 - layers spend at least a year in their accommodation and so need more space.

While intensively reared chickens live for around 42 days in cramped and stressful conditions, chickens raised to our standards cannot be slaughtered until they are at least 81 days old, unless they are defined as being a slow growing or traditional strain, when they can be slaughtered earlier.