Relationships in broiler chickens between lameness, liveweight, growth rate and age.

Thirteen genotypes of poultry were selected to represent a wide range of growth profiles and were fed either a non-limiting or Label Rouge diet. The birds' degree of lameness and liveweight were measured after 54 and 81 days. The birds reared on the Label Rouge diets were less lame than birds of the same genotype reared on the non-limiting diet. More traditional and slower growing genotypes tended to be less lame than the modern genotypes reared on the same feeding regimen. All the birds, irrespective of their genotype or diet, were less lame after 54 days than after 81 days. However, when liveweight was included in the analysis as a covariable, many of the differences disappeared. Only age at assessment significantly affected the walking ability of the birds, with the birds being approximately 0.6 units of gait score worse at 54 days of age than at 81 days. The regression coefficient between gait score and liveweight was 1.262 at 54 days and 1.128 at 84 days. The results indicated that liveweight was an important determinant of lameness in the diverse range of genotypes examined, that growth rate was also an important determinant of lameness and that younger birds may be more sensitive to differences in liveweight than older birds.