Is straw enough to prevent behavioural disturbances in caged pigs

With a view to the evaluation of different kinds of cage stalls, 32 pregnant pigs were kept in different housing systems (cage stalls were 65 and 85 cm wide, and there were two kinds of group housing) and under different treatments (increasing amounts of straw given after feeding). Ethological parameters were based upon the concept of behaviour as a Natural System, and recorded by a combination of scan sampling and continuous recording. Adrenal function was assessed by subjecting the sows to anaesthesia. The sows were examined weekly with respect to skin and claw lesions. As expected, the cage stalls prevented the sows from nearly all kinds of exploratory and appetitive behaviour, social interactions and retreat. Hindered locomotion occurred mainly before feeding, defecation, lying down and/ or in association with agonistic interactions. The caged sows frequently interrupted their lying down movements, indicating conditioned aversive states over which the animals have no operating control. Depending on the measures of the stalls in relation to body size, the sows' lying positions were more or less abnormal. Four out of 16 caged pigs performed abnormal oral activities, such as bar biting, bar 'wiping', trough biting, trough 'wiping' and sham chewing. In these individuals, plasma cortisol concentrations were not elevated after anaesthesia. However, the frequency, duration and stereotypy of disturbed behaviours increased, in spite of increasing amounts of straw given to the animals after feeding.