Sucker and weaner pigs prefer brick shaped enrichment blocks over cube or wedge shaped enrichment blocks

Environmental enrichment is provided to captive zoo animals to improve welfare by increasing the frequency and diversity of (natural) behaviours (Newberry 1995). According to De Jong et al. (2000), pigs require manipulable objects or bedding for stimulation. Most often this is provided in the form of straw. Under commercial conditions in Australia, providing such enrichments can be problematic since the conventional indoor, pig-pen environment is not compatible with straw or other bedding, in particular during the sucker and weaner phases. An enrichment block originally developed for sows during gestation, was reformulated to reduce hardness, and reduced in size and weight, to suit sucker and weaner pigs (Ridleys Corporation Ltd, Toowong, Qld, Australia). We investigated the effect of enrichment block shape on oro-nasal contact by sucker and weaner pigs with the block, and whether pigs habituated to the blocks over time. We hypothesised that the brick-shaped block would induce more contact than the cube or wedge as it would stimulate facilitative (co-operative) group behaviour and that interest in the blocks would be maintained for at least 24 h.

The experiment was conducted at the May Farm pig unit, Camden, NSW, with 19 Large White × Landrace litters containing 197 piglets from 10 days to 9 weeks old. Litters remained together throughout the experiment, with weaning occurring at about d 26. Litters were allocated at random to one of three block-shape treatments: (1) Cube; (2) Brick; or (3) Wedge. Pigs and enrichment blocks (one block per pen, fixed on 10 mm thick steel rod) were weighed weekly, and blocks were replaced weekly with the same treatment shape. Within litters, the number of pigs observed to interact oro-nasally with the enrichment block was recorded from video (AHDI Mega Pixel Cameras and AHD 1080P Digital Recorder, CCTV Central, Mount Waverley, Vic., Australia) using a point sample technique. Four focal pigs per litter were also marked enabling quantification from the video of bout duration of interactions with the blocks. Interactions were recorded on each minute over the first 30 min after block replacement, on each minute over the first 5 min/h for the next 23 h after block replacement, and on each minute over the first 5 min/h on the fourth day after block replacement. Behaviour data were analysed using Generalised Linear Mixed Models while weight data were analysed with Linear Mixed Models in REML (Genstat 17, VSN International, Hemel Hempstead, UK).

Brick-shaped blocks attracted more oro-nasal contact (17.0% probability during observations) than cube and wedge shapes (13.2% and 12.7%, respectively; P = 0.002). While oro-nasal contact with the blocks was relatively infrequent before pigs were ~25 days old, thereafter there was a steady increase in interactions (P < 0.05). Further, the frequency of oro-nasal contact was greater (P < 0.001) if blocks were ‘fresh’ (i.e. during the first 24 h) compared to 4 days old, suggesting habituation to blocks occurred. From 25 to 60 days of age, the duration of oro-nasal bouts by focal pigs with the blocks was always longer (P = 0.014) during the first 30 min of exposure to a fresh block, than for the remainder of the first 24 h or on the fourth day after block replacement. The findings thus suggest habituation may have occurred as quickly as 24 h after the block introduction. The decrease in block weight within weeks was not affected by block shape (P > 0.05), nor was the decrease in block weight associated with pig weight change (P > 0.05).

Our data suggest sucker and weaner pigs preferred brick- to cube- or wedge-shaped blocks, and that habituation may have occurred after 24 h. Oro-nasal contact by sucker pigs with the blocks predominately commenced in the fourth week of lactation, suggesting that enrichment blocks may not be needed in the sucker stage until the fourth week of lactation. The brick-shape preference may be due to the wider surface available for oro-nasal contact, where multiple pigs could simultaneously interact with the block, stimulating facilitation of rooting/nosing behaviour. We speculate that simultaneous interaction with the brick-shaped block may be similar to a litter co-operatively massaging the sow’s udder before suckling bouts.