The development of lameness and bone deformity in the broiler following experimental infection withMycoplasma gallisepticumorMycoplasma synoviae

Abstract

Groups of eight 7‐day‐old Mycoplasma‐free broiler chicks were inoculated with one of two strains of M. gallisepticum (MG/S6, MG/B31/85) or one of two strains of M. synoviae (MS/B31/88 and MS/B94/91) into the left hock joint. Controls were similarly inoculated with sterile mycoplasma broth. The birds were assessed at 2, 3, 4 and 5 weeks of age (1, 2, 3 and 4 weeks post‐injection) for lameness and joint and limb lesions. At 5 weeks of age they were killed and examined for gross skeletal abnormalities and microscopic lesions of both hock joints. The in‐contact controls showed no joint swelling or lameness. The mycoplasma did not apparently spread to cause gross pathology in the joints of in‐contact control birds, or to other joints in a bird injected with mycoplasma. Each mycoplasma strain caused specific pathologies manifest as varying degrees of lameness, left hock joint swelling, bone deformity and differences in the severity of articular cartilage and chondrodystrophic growth plate pathology. Shortening and bowing of the right tibiotarsus in the birds injected with mycoplasma indicated unilateral increased limb loading contributing to bone deformity. Chondrodystrophy seen with three mycoplasmal strains may have contributed to bone deformity in these birds. Lameness appeared to be a consequence of either joint swelling and/or bone deformity resulting in mechanical dysfunction. The role of joint pain in the lameness was not determined.