STUDY OF LEG WEAKNESS IN 2 COMMERCIAL BROILER FLOCKS

The major causes of leg weakness/lameness were investigated in two mal e commercial broiler flocks. The numbers of dead and lame birds culled from the flocks each day were recorded by the flock managers. Forty-f our lame birds and 22 sound birds were examined postmortem during a pe riod of six weeks and the proximal and distal end of each femur, tibio tarsus and tarsometatarsus were examined histologically, Attempts were made to isolate bacteria and viruses from the proximal end of each fe mur, Blood samples were examined for antibodies to chicken anaemia vir us (CAV), infectious bursal disease virus (IBDV) and Mycoplasma specie s. Bacterial chondronecrosis with osteomyelitis was identified in the proximal end of the femur of eight of the 44 lame birds, and in the pr oximal end of the tibiotarsus of a further bird (20.4 per cent). Gram- positive bacteria were present in all the lesions, Staphylococcus aure us was recovered from 62.5 per cent of the lesions confirmed by histol ogy, Bacterial chondronecrosis associated with S aureus has thus been identified as an important cause of leg weakness in these commercial b roilers. Lesions suggestive of the condition were visible macroscopica lly in only 11.1 per cent of the cases subsequently diagnosed by histo logy and bone histology is therefore required before a diagnosis can b e excluded. Angular limb deformities (13.6 per cent) and spondylolisth esis (11.4 per cent) were the most common macroscopic lesions identifi ed as causes of lameness. The overall incidence of tibial dyschondropl asia was similar in both the lame and sound broilers, but severe lesio ns were found only in lame birds (4.5 per cent).