ECONOMIC losses due to carcass defects which cause downgrading of broilers are of great magnitude, having been estimated at about twice that due to condemnations (Crothers and Helbacka, 1960). In a study of causes of such defects of broilers, Crothers and Helbacka (1960) found that bruises accounted for the largest number of downgrades. The second largest number of downgrade birds was listed as those caused by breast blisters; while the fourth highest group was caused by misbleeding or general discolorations.Although about 90% of bruises on commercial broilers are inflicted less than 13 hours prior to slaughter (Hamdy et al., 1961a), there are indications that flock management conditions might influence susceptibility of birds to bruising (Ringrose, 1953; Kaiser and Smith, 1958; Hamdy et al., 1961b).Breast blisters apparently are caused by physical irritation of the keel, since incidence and severity of the condition can be increased by simple increase in…