Pig Enrichment Science
The science of enrichment for pigs has advanced significantly, moving beyond simple observation of "pigs use this" to understand why certain enrichment works, how preferences develop, the role of novelty, and what practical provision best meets pigs' complex behavioural needs. This evidence base should guide on-farm enrichment decisions.
What Makes Enrichment Effective
Research identifies substrate characteristics that predict enrichment effectiveness: manipulable (can be moved, torn, rooted through); destructible (can be broken down over time); investigable (offers varied sensory stimulation through texture, smell, taste); and edible (provides some nutritional component). Straw consistently outperforms non-organic materials because it combines all these properties.
Enrichment that only provides one or two of these properties — a metal chain, a hard rubber toy — provides some benefit but does not fully satisfy the rooting motivation. Chains show rapid habituation and limited long-term impact on welfare indicators compared to organic materials.
The Novelty Effect and Habituation
Pigs show strong novel object responses — initial investigation of new enrichment items is intense but declines with familiarity. Habituation to enrichment reduces its effectiveness over time. This novelty effect means: rotating enrichment types maintains engagement; introducing new items alongside familiar ones combines novelty benefit with continued access; and different presentation of familiar materials (hanging vs. floor-scattered straw) can refresh engagement.
Long-term provision of substrate enrichment (straw bedding) shows more sustained welfare benefit than object-based enrichment because the substrate is continuously renewing (eaten, scattered, soiled material replaced) rather than a fixed object.
Preference Hierarchies
Pig preference testing shows consistent hierarchies: loose, destructible organic materials (straw, peat, compost, hay) are strongly preferred over non-destructible objects (chains, rubber toys). Among organic materials, straw (especially long straw) and peat rank highest in most studies. Novelty interacts with preference — novel items receive more investigation regardless of their position in the preference hierarchy.
EU Enrichment Requirements and Evidence
EU legislation requires provision of "permanent access to a sufficient quantity of material to enable proper investigation and manipulation activities" — interpreted as requiring organic manipulable material for pigs. The scientific evidence underlying this requirement is strong, and farms implementing adequate organic enrichment consistently show lower tail-biting rates, reduced aggression, and improved welfare scores.