The effects of prior experience of straw and the level of straw provision on the behaviour of growing pigs

Straw improves the welfare of pigs housed in barren environments as it can act as a recreational and/or nutritional substrate and provide for physical and thermal comfort. However, it is unknown how much straw must be provided to be behaviourally rewarding and whether pigs' prior experience of straw can effect their behavioural development. Therefore, the aim of the current experiment was to investigate these issues by exposing pigs which had, or had no prior experience of straw to four levels of straw provision (none, minimal, substantial or deep). Groups of pigs with prior experience of straw bit other pigs more when straw was not provided than groups of pigs with no such prior experience (P < 0.01). When pigs had no prior experience of straw, the expression of tail biting (P < 0.05) of other pigs was elevated for 3 weeks after being moved into growing/finishing accommodation. The quantity of straw-directed behaviour was found to be proportional to the amount of straw provided and an increasing amount of straw was found to result in an increase (P < 0.001) of rooting and ploughing and a concomitant decrease (P < 0.001) in nosing other pigs, aggression, ear chewing, licking other pigs, biting other pigs, belly nosing and tail biting and also play fighting (P < 0.05). These results suggest that moving pigs from previously strawed accommodation to unstrawed accommodation increases the occurrence of adverse pen-mate-directed behaviour and that when pigs have had prior experience of straw, even a small quantity of straw in the growing/finishing accommodation may serve to ameliorate the negative effects of the change in housing environment. Increasing the quantity of straw provided, reduces the occurrence of potentially damaging behaviours, but may not affect the diversity of straw-directed behaviour. (C) 2002 Elsevier Science B.V. All rights reserved.