Twenty-five years of selection for improved leg health in purebred broiler lines and underlying genetic parameters

Leg health is an important component of broiler welfare and the economics of broiler production. This study presents the development of leg health in 3 purebred commercial broiler lines during 25 yr of selection and investigates the genetic background of leg health traits in current populations of these lines. The leg health traits were deformities of the long bones (LD) and crooked toes (CT), recorded since 1985, and tibial dyschondroplasia (TD) and hock burn (HB), recorded since 1990. The prevalence of CT and HB decreased mainly in the first decade (range among lines -1.2 to -2.3% and -1.3 to -1.5% per year, respectively), after which it stabilized at low levels. The prevalence of LD and TD decreased by -0.6 to -0.9% and -0.4 to -1.2% per year, respectively. Genetic parameters were estimated using data from 4 recent generations. The BW ranged from 2.0 to 2.4 kg at 5 wk of age; the prevalences of LD, CT, TD, and HB from 8.6 to 12.9%, 0.6 to 2.6%, 4.6 to 8.0%, and 4.0 to 12.2%, respectively. Estimates of heritability were 0.04 to 0.07 for LD, 0.01 to 0.10 for CT, 0.10 to 0.27 for TD, and 0.06 to 0.09 for HB (all SE ≤0.01). Estimates of the genetic correlations between LD and CT were 0.11 to 0.43 (all SE ≤0.09), between these traits and HB were negligible, and of TD with LD, CT, and HB were -0.26 to 0.16 (all SE ≤0.11). Estimates of genetic correlations between the leg health traits and BW were lowly to moderately unfavorable, ranging from 0.09 to 0.37 (all SE ≤0.06). The differences between the lines suggest that strategies for simultaneous improvement of all traits tailored for each line individually have been effective. This research demonstrates the long-term effectiveness of selection for improving leg health in broilers and highlights that, despite somewhat unfavorable genetic correlations with BW, these traits can be improved simultaneously in a balanced breeding program.