Relationships between leg disorders and changes in the behaviour of broiler chickens.

The relationships between the severity of lameness, the presence of tibial dyschondroplasia, and the frequency of dustbathing behaviour and duration of tonic immobility were studied in 96 broiler chicks kept from day-old in groups of four in wire-floored cages. Dustbathing was observed when the birds were given access for one hour to a tray containing sand or straw. The duration of tonic immobility and the severity of lameness were scored during weeks 3, 4, 5 and 6. After slaughter at 41 or 45 days of age the birds were examined for tibial dyschondroplasia; 34 birds were classified as having tibial dyschondroplasia and 54 had detectable lameness problems. Birds with tibial dyschondroplasia had a higher lameness score (P < 0.001), dustbathed on fewer days (P < 0.0001), and had longer periods of tonic immobility (P < 0.03) at six weeks than birds which did not have the condition. However, almost all the chicks, including those with tibial dyschondroplasia dustbathed on day 27 after they had not been given access to the tray for three days, significantly more than on days when they had not been deprived of the tray (P < 0.0001). Furthermore, lame birds and birds with tibial dyschondroplasia also dustbathed less with age. Studies of the vertical wing-shaking element of dustbathing confirmed that tibial dyschondroplasia reduced dustbathing (P < 0.05) and also showed that during the one-hour tests, sand resulted in more dustbathing than straw (P < 0.01).