Efficiency to complete the maze test is decreased in young pigs enriched during the sucker phase

Numerous studies have explored whether pigs housed in barren versus enriched environments differ in the ability to learn and hold short-term memory (Kornum and Knudsen 2011). Most of the environmental enrichments provided in recent studies are not easily applied in a production setting, e.g. alternative penning systems and straw bedding (de Jong et al. 2000). In this study the authors used pig enrichment blocks that were specifically formulated for use with sucker and weaner pigs (Ridleys Corporation Ltd, Toowong, Qld, Australia). The enrichment blocks were malleable, edible, and degradable, at different stages of the sucker and weaner phase. It was hypothesised that providing enrichment in the sucker and weaner phases would improve pig cognitive ability, assessed via the pigs’ ability to learn and navigate a maze.

At 1 week old, four focal piglets (Large White x Landrace) from 72 litters over three replicates (n = 288) were selected and allocated to either the enriched or barren treatment group. Enriched litters were given one enrichment block per four piglets in the litter, placed unfixed in the farrowing crate. Barren litters received no enrichment blocks. At weaning (18.7 ± 0.1 days), the litters and the four focal piglets from the litters were split into treatment groups, two into enriched and two into barren treatment pens. Thus there were four treatment groups per replicate consisting of: enriched during weaner and sucker phase, enriched during sucker phase only, enriched during weaner phase only and no enrichment provided during both phases. During weaner phase, pigs were housed in groups of 24 and enriched pens were given one block per four pigs, unfixed, replaced weekly. Pigs were handled consistently across replicates and treatments. At 7 weeks of age, 18 pigs from each treatment group were exposed to a maze test. The maze arena measured 4.7 m × 2.0 m and consisted of an internal pathway constructed from metal mesh panels. This included two ‘traps’ (1.4 m × 0.75 m), designed to hinder pigs movement through the maze arena. Pigs could see two companion pigs through the maze, which incentivized their movement through the maze and a reward of whipped cream was provided at completion of the maze. Each pig was individually tested four times in the maze in 1 day. The time pigs took to emerge from the starting box, number of times traps were entered, the total time spent in the traps, and time to reach the end were recorded. Data were analysed using a general linear model in ASReml (ASReml v4, VSN International, Hemel Hempstead, UK), with treatment/test number as fixed effects and pig as the repeated-measure.

All pigs completed the maze except one. Pigs that were enriched as weaners, regardless of treatment grouping, emerged quicker from the starting box (P < 0.05). There were no effects of enrichment on the number of traps entered or total time spent in traps. However, there were trends for pigs that were enriched during the sucker phase taking longer to complete the maze than pigs housed in barren conditions during the sucker phase (Predicted Means 41.7 ± 1.1 s and 34.7 ± 1.1 s respectively, P = 0.053), and for females finishing quicker than males (Predicted Means 34.4 ± 1.1 s and 41.5 ± 1.1 s respectively, P = 0.056).

Enrichment had only minor effects on behavioural responses of the pigs in the maze test. However, an interesting trend was noted that pigs provided with enrichment in the sucker phase move slower through the maze. These pigs may have been less fearful when placed in the novel maze environment, and the decreased fear response may have allowed more explorative behaviour, hence the slower movement through the maze. Similarly, the gender difference in time taken to navigate the maze could indicate a superior learning ability of females or simply a greater motivation to reach the reward provided. The impact of enrichment on cognitive function and the use of the maze as a cognitive test to determine the effects of enrichment on pigs requires further study.