Bone mineralization in male commercial broilers and its relationship to gait score

Broilers selected for increased body size and breast muscle have imposed stress on the skeletal system, resulting in poorer walking ability. Our objectives were to determine the relationship between bone mineralization and gait score in 4 crosses of commercial broilers and to ascertain if mineralization of the toe is correlated to the tibia. Three chickens per pen each with good (gait score of 0 or 1) or poorer (gait score of 3) walking ability were killed and weighed. The left humerus, the left middle toe, and both drumsticks were collected for determination of bone mineral density (BMD), bone mineral content, and bone size traits using dual-energy x-ray absorptiometry. The BMD and bone size traits were similar among the 4 crosses of commercial broilers at 6 wk of age. However, gait scores differed among genotypes, with cross C having better gait scores than crosses A and B, but did not differ from cross D. The bone mineral content and bone size traits did not differ between birds with good walking ability as compared with those broilers of poorer walking ability. However, birds with poorer walking ability had higher BMD (P<0.05) and BW (P<0.001) than males with good walking ability. Within a cross, the correlation between gait score and BMD was not significant except for cross D birds. Broilers of cross D with better walking ability had decreased bone mineralization (r=0.19, P=0.03). The stronger correlation between gait score and BW for all crosses of commercial broilers (r=0.38, P<0.0001) suggests that the low association between gait score and bone mineralization for cross D was mainly due to BW. The BMD of the left toe was correlated to the BMD of the left tibia (r=0.91, P<0.0001) and right tibia (r=0.87, P<0.0001). In conclusion, bone mineralization was similar among crosses of meat-type chickens, and it had little influence on the gait score of male broilers.