Hundreds of chicken farmers are moving to free-range or the RSPCA Freedom Food production schemes to meet the increased demand from supermarkets.

From a commercial point of view, it makes sense to please customers, especially when many are willing to pay more for free-range birds. But switching production methods can be difficult and expensive.

Building larger sheds for the birds requires planning permission and a typical one of 30,000 square feet (2,800 sq m) can cost £500,000. but the farmer must also have sufficient land on which the birds can roam during the day. A shed of this size will house 30,000 free-range birds, 39,000 Freedom Food birds and 54,000 chickens for standard production.

Although large commercial free-range producers will rear 50,000 birds, the average producer keeps between 2,000 and 10,000 birds, and many family farms keep only 1,000. Free-range birds spend most of the day outdoors and are locked up at night. They tend to be more frisky and energetic and like to perch and roost, and even listen to music. They are also vaccinated against the common Gumborough disease, but average mortality rates are 3.5 to 4 per cent. Being outside can leave them prone to predators and bugs and diseases such as salmonella and avian flu.

Free-range birds are usually reared for 56 days, weigh about 2.4 kilograms (5.3lb) at slaughter and are sold for 98p per kilogram.

It is cheaper for chicken farmers to move to Freedom Food production, a scheme approved by the RSPCA, because they can install windows into existing sheds easily to give the birds access to daylight and six hours of darkness each night.

Freedom Food birds are put in sheds at one day old and are reared for 49 days. For four weeks they are fed on a ration of wheat, barley, soya and vitamins, but for the last 21 days they are put on a lower-protein diet. They will weigh 2.1 kilograms at slaughter and are sold at 86.3p per kilogram.

Standard chickens are crowded into sheds up to a maximum of 1.8 birds per square foot. They are reared for 42 days, weigh about 2.6 kilograms at slaughter and are sold for 73p per kilogram. They are fed on wheat, soya, barley and vitamin rations.

Many shoppers can still only afford to buy birds reared in standard conditions, and farmers who switch to free-range or Freedom Food birds are gambling on whether shoppers will be willing to pay more for kinder production methods in harder-pressed times.

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