Comparative clinical and morphological studies on the incidence of tibial dyschondroplasia as a cause of lameness in three commercial lines of broiler chickens

Tibial dyschondroplasia (TD) is the most common skeletal anomaly associated with fast growth in broiler and turkey lines and often results in the occurrence of bone deformation and lameness. It is a fairly common cartilage defect associated with the prehypertrophic cartilage of the growth plate being retained in the metaphysis. The objective of this investigation was to determine, through the use of pathomorphological methods, the prevalence of TD lesions that lead to lameness in 3 commercial broiler lines grown in Bulgaria. The study involved 20 broiler flocks with approximately 17,000 birds per flock and included flocks of Ross 308, Cobb 500, and Pureline broiler chickens. The initial age-related occurrence of TD-associated lesions averaged 23.7 d for Ross 308 flocks from 18 to 34 d of age, 19.6 d for Cobb 500 flocks from 16 to 23 d of age, and 28.8 d for Pureline flocks from 22 to 34 d of age. The number of observed macroscopic TD lesions in the Ross 308 broilers was 355 (24.22%), of which 203 (13.74%) were found in males and 152 (10.28%) were found in females; the number of lesions for Cobb 500 broilers was 185 (24.22%), of which 73 (10.48%) were found in males and 112 (16.09%) were found in females; and the number for Pureline was 313 (27.7%), of which 187 (16.54%) were found in males and 126 (11.16%) were found in females. A comparatively high prevalence of TD lesion-associated deformities was found in the proximal tibial metaphysis. There was a relatively low prevalence of TD lesion-associated proximal tibiotarsal fractures. We suggest, based on the results of our field investigation, that macroscopic TD lesions are developing at younger ages than reported previously. In the commercial broilers involved in the study, the prevalence of TD lesion-associated proximal tibiotarsal deformities was relatively high, and this condition involving TD lesion development potentially has severe consequences leading to lameness in broiler chickens.