Preening behaviour in laying hens has not been studied in detail, despite its association with dustbathing and possible role in feather pecking. After defining the components of the behaviour and determining the bout analysis criterion, this project examined preening behaviour and preen gland function, and how they were affected by bird age, beak treatment, and other external influences. In layer pullets studied to 19 weeks of age, preening was evident within the first few days of life, and maintained an (albeit small) part of their daily behavioural repertoire. Times spent in preening, and in all other behaviours observed except dustbathing, were affected by bird age. The only effects of beak trimming (at 8 days of age) on preening were on times spent directed at the back (in sit posture) and preen gland (in stand and sit postures), with trimmed birds showing more than non-trimmed birds. Beak trimmed birds spent less time in litter directed activity than non-trimmed birds. External influences such as frustration of feeding, feather pecking, presence of others (synchronisation), and type of floor substrate had little effect on preening, but variation in time spent preening between individuals was high. Preening observed during frustration of feeding could not be distinguished from normal preening, and so there was no evidence for classifying some preening as displacement behaviour. There were some differences in time spent preening between feather pecker and feather pecked status birds, but feather pecked birds did not preen more than non-feather pecked birds, as predicted. Groups of pen-housed layer pullets showed synchrony of preening at all ages observed, particularly when the proportion of time spent preening was high. Despite the association with dustbathing and the removal of stale feather lipids, times spent preening or dustbathing did not vary between birds housed on wire or litter floors. Peaks in preening and dustbathing were closely related in time, suggesting an association between them. Preen gland morphology and histology were affected by bird age and size, but not by floor substrate. Older birds may be experiencing preen gland congestion, as Judged by the solid consistency of preen gland contents. Feather lipid concentration was strongly affected by floor substrate when petroleum ether was used as the extractant, with some differences with bird age. Preen oil composition was affected by bird age and source of lipid (preen gland or feathers) but only 3 differences were detected with feather pecking and feather pecked status. These findings suggest that time spent preening is variable between individuals and changes with age, but is not greatly affected by the external factors tested here. Preen gland development is closely related to bird age, but the only great effect of external influences appears to be that of floor substrate on feather lipid concentration. Presumed sebaceous secretions from the skin may also influence feather lipid level, feather lipid composition, and plumage odour
