An animal welfare group is calling for better living conditions for factory-farmed chickens after lame birds chose to eat food containing painkillers.

Compassion in World Farming (CIWF) wants new welfare laws after scientists carried out studies on factory-farmed animals crippled through being forced to grow abnormally quickly in overcrowded conditions.

The new study, published in the Veterinary Record, showed the birds actively seek pain relief. It found that when given a choice of two feeds, one containing the pain-relieving drug carprofen, and one without, more lame birds than fit birds chose to eat the drugged feed.

And the more lame the chicken, the more its intake of drugged feed increased.

Eating the painkiller-added feed also significantly improved the walking ability of otherwise lame chickens. Researchers concluded that: "Lame broiler chickens are in pain and this pain causes them distress from which they seek relief."

Code of practice

CIWF now wants laws to improve the welfare of the 800 million broiler chickens reared for meat every year in the UK.

It is urging Farm Animal Welfare Minister, Elliot Morley, to back Labour MP Ann Clwyd's private members Bill when it is debated in the Commons on Friday, 7 April.

In a letter to Mr Morley, CIWF's political and legal director, Peter Stevenson, says: "This latest scientific evidence suggests that the serious lameness problems suffered by many chickens factory reared for the table are indeed painful.

"Compassion in World Farming believes that tough legislation is needed to tackle an enormous animal welfare problem.

"Mere government guidelines in the form of a revised code of practice, as currently proposed, will do little to alleviate this widespread animal suffering."