Effect of unilateral weight-bearing on pelvic limb development in broiler fowls: vascular studies

Fifteen broiler fowls which habitually adopted a unilateral weight bearing stance were studied. In the majority of fowls the left pelvic limb was weight bearing and the right limb showed severe angular deformity. Dyschondroplasia occurred most frequently in the load-bearing limb. In the load-bearing limb the majority of lesions were in the femur and proximal tibiotarsus. In the non-load-bearing limb lesions most frequently occurred in the bone extremities of the distal tibiotarsus and proximal tarsometatarsus. Occluded epiphyseal vascular canals occurred in conjunction with physeal thickening at some dyschondroplastic sites. The majority of dyschondroplastic lesions contained elongated penetrating epiphyseal vessels and vessels derived from the perichondrial ring. These vessels were associated with chondrocyte hypertrophy and matrix calcification, which was considered to lead to the repair of the lesions. There was minimal calcification of cartilage at the base of the dyschondroplastic lesions and the underlying metaphyseal vessels were blunt ending. This suggested that a band of abnormal physeal cartilage was acting as a barrier to penetration by the metaphyseal vessels and so preventing subsequent endochondral ossification.