Introduction
Environmental enrichment provides an opportunity to improve the living conditions of farm animals. Current farming systems offer little stimulation, other than food and water and animals are often closely confined in groups (with relatively little space per animal). Such environments may be inadequate to fulfil all the needs of an animal, or an animal may be unable to cope effectively. Enrichment can be used to encourage more of the natural behaviors of animals, thereby enhancing their welfare.
Objectives
- To present a brief overview of what is environmental enrichment
- To explain the main behavioral motivations of pigs at different life stages
- To create an understanding on how effective enrichment can be constructed and provided to meet those motivations and stimulate desired – and prevent undesirable – behaviors
What is enrichment?
Environmental enrichment describes modifications to the living environments of captive animals with the aim of improving their biological functioning and subjective experiences, thereby benefitting their welfare (Newberry, 1995; Mellor and Webster, 2014). In practice, this means offering animals more complexity in their environments so that they can perform a broader range of behaviors that are important and more natural to them, for example, foraging for market hogs or nest building for sows. When they can perform such behaviors, it has a positive effect on the animal’s wellbeing.
The term environmental enrichment (or ‘enrichments’) is used widely and is often applied to anything that is added to a captive environment. However, from a scientific point of view, modifications should only be viewed as environmental enrichment when they actually improve welfare (van de Weerd and Ison, 2019). Well-managed enrichment strategies should not only focus on the immediate or short-term effects on the behavior of the animals, but also on long-term beneficial outcomes, such as on growth, health and farm economics.
What are the benefits of enrichment?
Complex environments offer animals more choice over how they would like to spend their time, adding to a sense of control, which can reduce stress. In addition, enrichment can also be used to prevent or manage undesirable stereotypic behavior (such as sham-chewing or bar-biting in sows). Stereotypic behavior develops in environments with few stimuli, physical restraint, fear, or frustration and is considered an indicator of welfare (Mason, 1991). Whilst the expression of sham-chewing is helping sows to cope with this type of stress, it can also affect their offspring through fetal reprogramming (Tatemoto et al., 2019).
The most well-known benefit of enrichment is to use it as a tool to prevent (or manage) damaging behavior such as tail-biting in market hogs, thereby reducing medical care costs and slaughterhouse condemnations. In addition, when pigs are not tail-docked at all, enrichment is essential and can provide a better profit margin over the whole production period, compared to docked hogs in impoverished environments (Chou et al., 2020).
Other beneficial outcomes from enrichment strategies are, for example, that enriched environments can create more robust animals that have an improved immune/health status (Backus and McGlone, 2018) with the potential to reduce health costs or they are able to better cope with weaning, reducing the growth dip after weaning and improving overall growth (van Nieuwamerongen et al., 2015).
Enrichment strategies for pigs at different life stages
Different types of enrichment strategies can be used to meet the needs of pigs. These needs will be dependent on the different life stages (such as sows and boars used for reproduction, young piglets, or market hogs), closely linked to the individual types of housing systems and management requirements for each stage.
This section highlights the main behavioral motivations that are important for different stages of swine production and how these can be addressed by environmental enrichment, and how welfare can be affected if these needs are not met. This will ultimately dictate the success of enrichment strategies. The information also includes some considerations on the provision of enrichment in practice.
Enrichment strategies for market hogs
Market hogs (growing pigs) are strongly motivated to perform behaviors that include exploration and foraging, i.e. to search for food (involving behaviors such as nosing, rooting and chewing) in their environment. With food readily available, there is less of a need to perform these behaviors. Pigs can get bored and frustrated and this can be expressed as undesirable pig-pig manipulation behaviors, such as tail- and ear biting (also called: harmful social behaviors), affecting their welfare (e.g. Fraser et al., 1991). Enrichment can reduce these types of undesirable behaviours, although the underlying mechanisms are still not completely clear (Buijs and Muns, 2019).
When selecting enrichment, there are some general principles that apply. The enrichment needs to meet specific characteristics to be effective. For growing swine, these characteristics are: manipulable, chewable (deformable, destructible), edible/ingestible (with an interesting texture, flavor or smell) (Van De Weerd et al., 2003). Particulate substrates with an organic origin (e.g. straw) and presented as floor covering (bedding) meet all these characteristics. However, bedding is not compatible with slatted floors, costs may be prohibitive and there may be biosecurity concerns, presenting barriers to uptake in current commercial practice.
The provision of easier and cheaper point-source enrichment is more common (i.e. discrete objects, such as wooden beams or chewable toys, presented in one location), but many of these materials are suboptimal in terms of their effectiveness (European Commission, 2016), as they do not incorporate a sufficient number of the previously mentioned characteristics to sustain the interest of the pigs. If point-source objects are presented, they are most interesting when they are deformable and suspended (Averós et al., 2010), another solution is to provide combinations of objects meeting as many of the characteristics as possible (Chou et al., 2019).
Enrichment can also be used as a tool to manage undesirable and damaging behaviours, such as tail biting. When the early signs of tail biting are seen (for example, a downward posture of the tail Zonderland et al., 2009), additional enrichment can be used in a corrective way to prevent escalation of the behavior.
Table 1 shows examples of enrichment for market hogs and some practical considerations.
[Insert Table 1 here].
Enrichment strategies for dry sows (in groups or stalls)
Gestating sows are strongly motivated to forage for food (nosing, rooting and chewing), as they are normally fed a restricted quantity of food. As a consequence, there is a risk that these animals show stereotypic behaviours (sham chewing, jaw stretching) (Verdon et al., 2015) and undesirable manipulation (vulva biting, aggression) which affects their welfare (Spoolder et al., 2009).
The nutritional status of sows combined with their strong social dominance relationships, will affect their motivation to interact with enrichment, requiring different types of enrichment compared to market hogs. For example, limited access to valued enrichment can result in greater aggression towards subordinate sows and higher stress levels in those animals (Stewart et al., 2008; Roy et al., 2019). However, this will be dependent on the type of enrichment provided and where it is offered (Greenwood et al., 2019).
Stereotypic behavior, such as sham chewing, remains challenging to address with enrichment and requires special attention, as hunger is such a strong internal driver (Stewart et al., 2008).
Table 2 shows examples of enrichment for dry sows (in groups or stalls) and some practical considerations.
[Insert Table 2 here].
Enrichment strategies for sows before farrowing and when nursing a litter
When close to giving birth, pregnant sows are strongly motivated to perform nest-building behavior and under natural conditions they would use organic nesting materials to do so
(Wischner et al., 2009). After giving birth, sows want to show maternal behavior, to nurse and interact with their piglets (Algers, 1993; Algers and Uvnäs-Moberg, 2007). The ability to build a nest is very limited when sows are kept in farrowing crates, and this is often expressed as restlessness, redirected nesting activity against the equipment or as oral/nasal stereotypies putting their welfare at risk (Damm et al., 2003).
Providing sows with nesting materials before farrowing so that they can perform nest-building behavior can reduce the duration of farrowing and it can also reduce the risk of crushed piglets because the sow does fewer postural changes (is calmer) during farrowing itself (Thodberg et al., 1999; Plush et al., 2021). Overall, this improves the maternal responses and social interactions with piglets and the welfare of sows (Vanheukelom et al., 2012).
Table 3 shows examples of enrichment for sows (with litter) and some practical considerations.
[Insert Table 3 here].
Enrichment strategies or piglets (before and after weaning)
Young piglets are strongly motivated to suckle, explore novel aspects of their environment, to learn (social) skills through play and to sometimes hide from others. These behavioral needs can be addressed through the provision of enrichment thereby enhancing their welfare
(Vanheukelom et al., 2012). Some studies have found positive effects of early life enrichment (e.g. straw, sisal ropes, chewing toys, wood shavings) on reducing tail biting when the pigs are older, although not all studies found these effects. After reviewing these studies, Prunier et al., 2020 suggested that the potential effects are determined by the nature of the enrichment materials provided pre-weaning, as well as the housing conditions after weaning. It is clear however that when enrichment such as chewable ropes and paper are provided, the piglets use these for nosing and mouth manipulation, with lower levels of manipulation of pen mates (Telkänranta et al., 2014), and potentially less (negative) manipulation of the sow as a consequence (Swan et al., 2021). Table 4 shows examples of enrichment for piglets (before and after weaning) and some practical considerations.
[Insert Table 4 here].
Enrichment strategies for breeding or teaser boars
Mature breeding and teaser boars are often overlooked as animals who also need enrichment for their wellbeing. Their specific housing and welfare requirements are poorly understood (Petak et al., 2010) and they are mostly housed individually with limited social contact, and sometimes (outside Europe), kept in stalls with very limited movement and distraction opportunities. The easiest form of enrichment is to provide a substrate bedding or other type of effective enrichment (see market hog section), bearing in mind that boars are strong and can destroy materials quickly.
In conclusion, environmental enrichment can be used to enhance living conditions thereby encouraging more of the natural behavior of pigs. It is recommended that animal welfare standards in farming systems include the provision of enrichment as a core part of best farming practices.
Summary
Environmental enrichment describes modifications to the environments of captive animals by adding more complexity, so that they can perform more (natural) behaviors that are important to them. Enrichment has the potential to improve welfare and create robust animals with improved health status and growth and should be considered. It is important to understand the main behavioral motivations of pigs at different life stages, so that effective enrichment can be provided. Enrichment for market hogs should address strong behavioral motivations such as exploration and foraging (searching for food) and preventing harmful social behaviors such as tail biting. Characteristics of effective enrichment are: manipulable, chewable (deformable, destructible), edible/ingestible. Gestating sows have an even stronger motivation to forage for food due to their restricted diets. Combined with their strong social dominance relationships, means that enrichment strategies need to pay attention to location, quantity and dominance aggression. Providing sows with nesting materials before farrowing addresses their nest-building needs and this can reduce the duration of farrowing, reduce sow posture changes and improve piglet survival. For young piglets, enrichment should allow exploration of novel aspects of their environment, learning of skills through play and hiding from others. Boars also need enrichment, similar to that for market hogs, but allowing for their size and strength.
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