Comparative development of the antitrochanter in three strains of domestic fowl

Lameness and musculoskeletal disease were more frequent in two strains of broilers (selected [S] and relaxed [R]) than in an unselected layer (J). Defective fibrocartilage accounted for 0.15 of the total area of antitrochanteric cartilage at 29 weeks of age in the S-strain birds. There was more retained hyaline cartilage in the R- and S-strain birds at 15 weeks, and at 22 and 29 weeks there was delayed ossification. Occluded blood vessels, death of chondrocytes and degenerate areas of fibrocartilage occurred only in the broiler strains; they were worse in the S-strain and degenerate fibrocartilage occurred more frequently and in larger amounts. The area, length and depth of cartilage were larger in the heavier strains but the differences were considerably smaller than the difference in their relative bodyweights. The degeneration of the antitrochanter appeared to be associated with a reduction in the blood supply to the underlying hyaline cartilage and with the death of chondrocytes and the degeneration of matrix within the fibrocartilage of the antirochanter.