Bacterial chondronecrosis with osteomyelitis and lameness in broilers: a review

This review focuses on a specific cause of lameness known as bacterial chondronecrosis with osteomyelitis (BCO) in broilers. Rapid increases in body weight impose excessive torque and shear stress on structurally immature epiphyseal and physeal cartilage, primarily in the proximal femora, proximal tibiae, and flexible thoracic vertebrae. Excessive mechanical stress creates osteochondrotic clefts among the chondrocytes of susceptible growth plates. These wound sites are colonized by hematogenously distributed opportunistic bacteria, culminating in the gross abscesses and necrotic voids that are pathognomonic for terminal BCO. Lameness attributable to characteristic BCO lesions can be reproduced by rearing broilers on wire flooring to create persistent footing instability and physiological stress, without the need to inoculate the birds with pathogenic bacteria that presumably are present but quiescent within the bird's microbial communities or in the environment. Experiments using the wire-flooring model revealed innate differences in the susceptibility of broiler lines to BCO, and demonstrated that BCO incidences can be reduced by prophylactically providing probiotics in the feed, by prophylactically adding 25-hydroxy vitamin D3 to the drinking water, or by therapeutically adding the antibiotic enrofloxacin to the drinking water. Hatchery and chick quality issues clearly influence the susceptibility of broilers to BCO. When broilers remain in a sitting posture for prolonged periods, the major arteries supplying their legs may be compressed. These episodes of inadequate blood flow may prevent chondrocyte maturation and trigger focal necrosis, thereby making the epiphyseal and physeal cartilage highly susceptible to osteochondrosis and BCO. Much remains to be revealed regarding the pathogenesis of BCO. Further revelations will be facilitated by the availability of the now-validated wire-flooring models that consistently trigger high incidences of BCO in experimental flocks.