The study was started in March 2002 and completed in 2005 and the full Project Report was published on the Defra website in February 2006. This is the first time it is published in a scientific journal.

The study was conducted by Bristol University with the full involvement of the main chicken producing companies in the UK, demonstrating their commitment to good bird welfare.

The study was intended to identify risk factors associated with leg health problems and to provide recommendations that may be used to improve leg health under commercial conditions.

Following on from the study, chicken producers have continued to work with Bristol and have changed flock management practices in line with the study's findings, according to the BPC.

These changes, such as longer dark periods to give the birds more rest, meal-time feeding in the earlier weeks, and the addition of whole wheat to chickens' feed have significantly improved overall leg health. Since the study was undertaken, new genetic stock has been introduced into the UK chicken sector which has improved the leg health of the breed highlighted in the study.

Some of the results of the Bristol study are at odds with the major Defra-funded project carried out by Professor Marian Dawkins of Oxford University at around the same time.

This study examined the effects of different stocking densities on chicken welfare. It used a different gait scoring system form Bristol and found little difference in leg health between 30kg/m2 and the Assured Chicken Production maximum stocking density of 38kg/m2. In the Oxford University study chickens whose walk was scored at a level considered to be a welfare problem were on average less than 1% of examined birds, and the score was not affected by stocking density.

All gait scoring techniques currently used to indicate chicken leg health are subjective which reduces their accuracy in scientific comparisons. The poultry sector is keen that objective gait measuring equipment be developed that will remove these subjective aspects and allow meaningful measurements between flocks and across years. Work is progressing on such a device, the BPC said.

"British chicken producers take welfare very seriously as the companies' full participation in these welfare studies demonstrates," a statement from the BPC said.

"Chicken producers heed the practical findings of these studies and implement them to improve the overall health and welfare of their flocks."