The effect of long or chopped straw on pig behaviour.

In the EU, pigs must have permanent access to manipulable material such as straw, rope, wood etc. Long straw can fulfil this function, but can increase labour requirements for cleaning pens, and result in problems with blocked slatted floors and slurry systems. Chopped straw might be more practical but what is the effect on pigs' behaviour of using chopped instead of long straw? Commercial pigs in 1/3 slatted, 2/3 solid pens of 15 pigs were provided with either 100g/pig/day of long straw (20 pens) or of chopped straw (19 pens). Behavioural observations were made of 3 focal pigs per pen (one from each of small, medium and large weight tertiles) for one full day between 0600 and 2300h at each of ~40kg and ~80kg. The time spent rooting/investigating overall (709s/pig/h at 40kg to 533s/pig/h at 80kg), or directed to the straw/solid floor (497s/pig/h at 40kg to 343 s/pig/h at 80kg) were not affected by straw length but reduced with age. Time spent investigating other pigs (83 s/pig/h at 40kg), the slatted floor (57 s/pig/h), or pen fixtures (21 s/pig/h) were not affected by age or straw length. Aggressive behaviour was infrequent, but lasted about twice as long in pens with chopped straw (2.3 s/pig/h at 40kg) as in pens with long straw (1.0 s/pig/h at 40kg, p = 0.060). There were no significant effects of straw length on tail or ear lesions, but shoulders were significantly more likely to have minor scratches with chopped straw (p = 0.031), which may reflect the higher levels of aggression. Smaller pigs showed more rooting/investigatory behaviour, and in particular directed towards the straw/solid floor and the slatted floor than their larger pen-mates. Females performed more straw and pen-fixture directed behaviour than males. There were no effects of pig size or sex on behaviour directed towards other pigs. In summary, pigs spent similar amounts of time interacting with straw/solid floor when long and chopped straw were provided, and most aspects of pig-directed behaviour and injuries were not affected by straw length. There was an increase in pigs with minor shoulder lesions with chopped straw, perhaps because of increased aggression. The use of chopped straw as an enrichment material for pigs warrants further investigation in larger and more detailed studies.