Comparison of the behaviour of piglets raised in an artificial rearing system or reared by the sow

Over the last 15 years, rising sow fertility has led to a considerable increase in litter size. As a consequence, the number of live born piglets may outnumber the number of functional teats, and surplus piglets are removed from the sow at the age of 3-6 days and fed with artificial milk. The objective of this study was to compare the behaviour of piglets raised in a commercially available artificial rearing system (group size: seven piglets) with that of piglets reared by the sow in a loose farrowing pen (seven focal piglets observed per litter). The behaviour of 98 piglets raised artificially (7 batches) and 82 piglets reared by the sow (6 batches) was videotaped on days 4, 11 (artificially raised piglets only) and 18 after introduction of the piglets to the artificial rearing system. Belly nosing, manipulation of a pen mate, play-fighting, aggressive behaviour and resting were assessed by continuous focal observation twice a day in the periods from 05:00 to 10:15 and from 13:00 to 18:15. Data were analysed by using linear mixed-effects models. Belly nosing was hardly ever observed in piglets reared by the sow, whereas the duration as well as the frequency of this behaviour increased between days 4 and 18 in piglets raised artificially. Moreover, artificially raised piglets spent more time manipulating a pen mate, showed less play-fighting, exhibited more aggressive behaviour and had shorter resting bouts compared with piglets reared by the sow. Finally, total duration of resting decreased from day 4 to day 18 in artificially raised piglets and increased in piglets reared by the sow. It is concluded that piglets removed from the sow at an early age and raised artificially redirect massaging behaviour to their pen mates, resulting in high levels of belly nosing and indicating impaired animal welfare. Moreover, the small space allowance in the tested artificial rearing system may additionally account for behavioural differences observed between artificially raised piglets and piglets reared by the sow in a loose farrowing pen. (C) 2015 Elsevier B.V. All rights reserved.