Referee 1's review (Marian Dawkins):

This is an important paper that deserves to be widely read in view of the scale of the work and the seriousness of the welfare problem involved. There are, however, two issues that the authors need to clarify before publication can be wholeheartedly recommended:
1) The authors seem to make the assumption that poor gait scores are entirely due to leg disorders. However, one of the major welfare problems with fast-growing broilers is cardiovascular disease, which could make even birds with good legs unwilling or unable to walk far without becoming exhausted. As this article is for a general audience, it would be important to explain whether and how the gait-scoring system distinguishes between birds that cannot walk through having leg disorders and those that cannot walk through exhaustion through cardiovascular disease. If the distinction cannot be made then the term 'Leg disorders' is inappropriate in the title. If the distinction can be made, it would be helpful to have this explained more explicitly.
2) Since broiler house managers walk round the houses regularly and cull birds with the poorest gaits, the numbers of birds scored as having poor gaits in a given house will inevitably be a function of the severity of the manager's culling policy. What I couldn't understand was exactly how this was factored into the results. Explaining this is quite important because otherwise the 'best practice' could simply be in line with the severest culling policy.

I regard these points as sufficiently important (particularly for a general audience) that they need to be explained before a final decision is made on whether or not to accept the paper.

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N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication the manuscript has been revised in light of these comments and to address other editorial requirements.