The objective of the present study was to investigate the relationship between rooting behaviour and foraging in growing pigs. In study 1, forty-eight 11-week-old pigs were housed in eight groups of six with access to a rooting substrate in the form of spent mushroom compost. In half of the groups the rooting substrate contained food rewards, and in the other half of the groups it did not. All pigs had ad libitum access to feed. In study 2, one hundred and ninety-two 11-week-old pigs were housed in thirty-two groups of six, all with access to spent mushroom compost, and eight groups were each fed to 70, 80, 90 or 100% appetite. Treatments were applied over a two-week period in both studies. The number of pigs involved in active rooting (rooting in substrate while standing), inactive rooting (rooting in substrate while sitting or lying) or non-rooting activity (standing in substrate area and involved in any activity except rooting) was recorded by scan sampling. These behaviours tended to reach a peak in the morning and again in the afternoon. Inactive rooting was not significantly affected by treatments in study 1 or study 2. Food rewards in the rooting substrate led to a significant reduction in active rooting behaviour and in non-rooting activity during peak periods of the day (P < 0.05). It is suggested that learned associations between rooting behaviour and acquisition of food caused the pigs to stop rooting when all the food rewards had been consumed. The fact that rooting was performed in the absence of nutritive feedback suggests that this behaviour is performed independently of its appetitive foraging function. Restricting feed levels to 70 or 80% of appetite led to a significant increase in active rooting and in non-rooting activity during peak periods (P < 0.05). The relationship between feed restriction and active rooting behaviour tended to be linear (P < 0.08). This suggests that levels of rooting behaviour are flexible in response to nutritional needs.

The nose-ringing of outdoor pigs (Sus scrofa), although commonly practiced as a means to inhibit rooting behaviour and therefore reduce pasture damage and soil erosion, has been questioned on ethical grounds and alternatives are being sought. In this experiment, the effect of overground environmental enrichment was assessed as a possible alternative. 12 multiparous sows were housed in groups of four and randomly allocated to one of three treatments in a 3 × 3 Latin square design. Treatments were: 1) no environmental enrichment, 2) edible overground enrichment in the form of grass silage, and 3) inedible overground enrichment in the form of branches and tyres. Sows that received silage as overground enrichment spent significantly less time rooting the paddock (P < 0.01) than did sows on the other two treatments. The absence of a significant difference between treatments in overall foraging time budgets suggests that the manipulation of edible substrates may substitute for rooting behaviour in outdoor sows.

In the EU, pigs must have permanent access to manipulable materials 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 straw instead of long straw? Commercial pigs in 1/3 slatted, 2/3 solid pens of 15 pigs were provided with either 100 g/pig per day of long straw (20 pens) or of chopped straw (19 pens). Behavioural observations were made of three focal pigs per pen (one from each of small, medium and large weight tertiles) for one full day between 0600 and 2300 h at each of ~40 and ~80 kg. The time spent rooting/investigating overall (709 s/pig per hour at 40 kg to 533 s/pig per hour at 80 kg), or directed to the straw/solid floor (497 s/pig per hour at 40 kg to 343 s/pig per hour at 80 kg), was not affected by straw length but reduced with age. Time spent investigating other pigs (83 s/pig per hour at 40 kg), the slatted floor (57 s/pig per hour) or pen fixtures (21 s/pig per hour) was 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 per hour at 40 kg) compared with pens with long straw (1.0 s/pig per hour at 40 kg, 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 exhibited 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.

Nose-rings are often fitted to outdoor commercial pigs to inhibit rooting and reduce consequent pasture damage. During ethological observations of the behaviour of ringed pigs at pasture, subjective impressions suggested that pigs with nose-rings picked up their normal feed, in the form of large nuts (‘roll nuts’), more tentatively than unringed pigs. The observed pigs were gestating sows under one of three treatments: unringed controls (UR), multiple wire ‘clip-rings’ through the upper rim of the snout (CR), or rigid ‘bull-rings’ through the nasal septum (BR). For formal assessment of feeding efficiency eight randomly selected pigs from each condition were timed and video-recorded, in individual feeder stalls, as they ate 20 3-cm long roll-nuts laid out in a standard rectilinear array in a steel-sided tray under each of five conditions: on a hard surface, on the surface of soil, on the surface of turf, embedded in soil, or embedded in turf. All groups took longer to eat up their test meal from the plain surface than from the surfaces of either soil or turf and longer still when the nuts were embedded. In all conditions, ringed pigs took longer to eat their 20 nuts than did controls, with BR > CR > UR (overall mean times, pooling data from the different feeding conditions: 118·6, 69·9 and 56·7 s respectively: P < 0·001). The difference between groups was greatest when nuts were embedded. Also, when nuts were embedded, ringed pigs were more reluctant to root: the latency to their first rooting action was delayed (mean latency across both embedded’ conditions: 29·6, 87·9 and 106·8 s for UR, CR and BR pigs, respectively: P < 0·01 with soil and turf conditions combined) and, even after starting, a smaller proportion of the residual trial time was spent rooting (0·11, 0·27 and 0·62 of the total time by BR, CR and UR pigs respectively; P < 0·001). It is concluded that nose-ringing depresses the efficiency with which pigs feed on solid food, especially if they have to root for it. The threat to welfare inherent in this will be greatest when ringed pigs are in direct competition with unringed pigs.