Do pigs play with chains? Science versus society


Scientists object to the suggestion that pigs may be playing with toys like metal chains in their pen. In ordinary language, however, it is perfectly fine to use the word play for such animal-material interaction. Apparently, the word ‘play’ has a more restricted meaning in science than in normal language. More words are used differently in science. In particular, words like stress and pain have been operationalised in science to allow scientific measurements without at the same time implying negative emotions or feelings. By contrast, play is often associated with positive emotions. This blog questions the scientific use of the word play and argues that pigs may play with chains much in the way humans can play with a pencil in their hands or can chew gum. However, when pigs are said to play with ‘enrichment’ materials like ‘toys’ it is not automatically implied that these materials are sufficiently enriching to induce positive emotions.


Many producers, suppliers and consumers tend to use the term ‘play’ to refer to object manipulation in pigs. Correspondingly, the word ‘toy’ is frequently used for point-source pig enrichment materials like chains, pipes and ropes in the popular press. I (MB) have used the word play, in particular referring to growing pigs interacting with a metal chain.
However, several applied ethologists have objected to this use of the word play, arguing that it is not in accordance with the conventional use of the term in science.
In applied ethology it is not generally accepted to say that pigs are playing with a chain. This is because play typically requires variability of behavioural elements and certain locomotor elements like being boisterous.
Play may roughly be divided in locomotor play and object play. This blog concerns the more static object play. Here, I will present a ‘dispute’ between science and society regarding the use of the term play to refer to object play like chain manipulation in pigs. I will try to clarify and specify the use of the word ‘play’ in science and ordinary language so as to inform interested readers, e.g.scientists pig farmers and the public, about the distinction, challenge the scientific convention a bit, and perhaps widen the scientific use of the word ‘play’. The central question then is: Is it proper to say that animals like pigs play with objects like metal chains? Do pigs ‘play’ with chains?

Neutral terms

To refer to object play scientists tend to prefer more neutral terms like ‘use’, ‘animal-material interaction’ (AMI), ‘oral/manipulative behaviour’ and ‘object-directed behaviour’.
This preference may derive both from a need to be able to measure/operationalise the term and from a reluctance to imply the presence of emotions. The latter has a long history in science in which behaviourism determined scientific thought. In this respect it is certainly more accurate, more neutral, more ‘objective’, more safe to say that a pig is engaging in AMI or showing object-directed behaviour, than to say that the pig is playing with the chain.
Linguistically, of course, it is more convenient and appropriate to use the word play than to ‘engage in object-directed behaviour’. However, in science accuracy takes precedence. But in the case of chain manipulation there hardly seems to be any ambiguity as regards descriptive accuracy, as it is very clear what is implied in terms of behaviour if it were referred to as chain play. Furthermore, when in science play typically requires variable behavioural elements, and if that is not what pigs do when they interact with chains, should we then avoid using the word ‘play’ (and perhaps even deny that pigs show much object play) or may we also question variability as a defining characteristic of play? The same goes to some extent for the requirement that play must be associated with positive emotions. I will come back to these points below.

Different meanings of words used in science and common language

For now it is sufficient to point out that the word ‘play’ seems to be used differently in science and in common language. Notable differences in word use between ordinary language and science are also found in the case of words like ‘pain’ and ‘stress’. These words are heavily loaded with a connotation of (negative) feelings, namely pain and stress respectively. However, this is not what scientists want or can imply when they record nociceptive responses or stress hormones. Since empirical science is focusing on observable phenomena and since emotions cannot be measured, scientists have previously preferred to avoid implying emotions altogether. Hence, the scientists’ preference for operational definitions may have resulted divergences from common language. The divergence, however, is not necessarily restricted to (a denial of) emotions as it also applies to words like ‘fit’ (as in ‘survival of the fittest’) and ‘flu’ (which in science, but not in every-day life, requires the presence of influenza virus). In these cases the divergence originates in the scientists’ need to use clearly defined operationalised concepts that allow uniform measurements. But in the case of object play, there doesn’t seem to be much of a need for an operational divergence between science and ordinary language, if we could agree to use the word to refer unambiguously to the object-directed behaviour that is being observed.

Feeding and drinking

In relation to this it also seems relevant to point out that science does not always seem to be consistent in applying its own principles either. For if it were absolutely necessary to stick to directly observable phenomena, then it would be unscientific to use terms like ‘feeding’ and ‘drinking’ in behavioural science. However, ethologists have no problem using these terms when they in fact only record ‘head-in-feeder behaviour’ or ‘head-towards-drinker behaviour’. As, while these behaviours will mostly indicate feeding or drinking activity, we cannot be absolutely sure. Perhaps, in fact, some feeding or drinking may actually be playing with food or water!

Technical definition

A related point here is that it is commonly accepted in science to use technical definitions. So, as it is allowed to use the term ‘feeding’ for ‘head-in-feeder behaviour’, so it should be allowed in science to state in the methods section of a paper that the authors will use the term ‘play’ to refer to ‘object-directed behaviour’. A more general adoption of such a convention would in the end sanction the use of the term ‘play’ to refer to object interaction/manipulation. Note: I’m not arguing that we should use the word play, but I’m pointing out that we could, if we so preferred, and as it so happens I do if only because it sounds better linguistically (and I don’t see major reasons not to).

Exploration as underlying motivation

Scientists tend to classify object play as a form of exploratory behaviour. But is this correct?
Exploration implies there is something to learn (goal-directed information gathering). But what would a pig learn from manipulating a metal chain? A rope is attractive to pigs because it can be destroyed. But what kind of exploration is involved in manipulating the same chain over and over again, or even in destroying a similar kind of rope over and over again? The object-directed behaviour that starts as exploration, may at some point stop being (primarily) motivated as such.
Related forms of pig enrichment raise similar concerns. For example, floor feeding or providing a handful of straw or maize silage. Is that exploration? Or is that just feeding behaviour? These materials are typically called enrichment materials, however, thereby slightly implying they result in exploration and a related motivational state, despite the fact that this is certainly questionable.
There is actually a very fine line between one form of object play and another. Take a chain. Pigs mostly interact with the end of the chain, i.e. the last links/shackles. Does it matter, if the shackles are attached to a chain, or loose, in order to call it exploration or play? Suppose the shackle is a small pebble, on which pigs, esp. outdoor sows, may root, bite and orally manipulate for prolonged periods of time. Is it exploration? Should we just call it ‘use’, or perhaps even classify it is ‘abnormal behaviour’? I don’t seem much harm in calling it ‘play’.
In fact, it may be questioned whether scientists really need to be able to establish the underlying motivation before they can label a behaviour properly. For example, mounting is commonly listed as a behavioural element, even though, especially in younger pigs, it is often not clear whether such behaviour is indeed sexually motivated. For walking it is even more evident that scientists do not require knowing what is the underlying motivation before the behaviour can be labelled as walking. Behavioural elements may simply have different underlying motivations. So it may not be a problem to label chain manipulation as play and at the same time allowing for the possibility that the animal may be exploring the chain to some extent at the very same time. In fact, it may also be acknowledged that it is not even certain that chain play is not at the same time stereotypic and perhaps indicative of stress and negative welfare. However, when frustration clearly has the upper hand, as seems to be the case in pigs trying but failing to grab and bite a hanging ball or wood, then I would personally prefer to avoid using the word ‘play’ as a label, even though the causal motivation initiating the behaviour may well be/have been a motivation to play.

Variability and locomotion

Classic, scientific definitions of play (e.g. Burghardt 2005) suggest that if the interaction with the chain has characteristics of play and is accompanied by other behaviours typically classified as play (e.g. running; twisting; flopping; play fighting) then perhaps yes it can be defined as play – but it might equally have a different underling causation (esp. exploration or foraging). Scientists would want to see that unpicked before deciding what behaviour class it falls into, even though they recognise that these functions may overlap to some extent.
It may be questioned, however, if it is necessary for object play in particular to be variable, developmental and involve locomotor elements like running, twisting and play fighting.

Human play

In ordinary life the term ‘play’ is notoriously difficult to define (Wittgenstein 1953) and often used for a variety of human behaviours. Some of these can be very much focussed (hence lacking variability) and involve very little locomotion. Playing a game of chess would be a typical example. By contrast, other types of play may involve a lot of locomotion, but still be extremely serious, even quite emotionally negative at times, and following fixed rules, like playing a game of soccer.
Some of these play behaviours are very difficult to distinguish from serious adult behaviour as indicated by the level of seriousness of being engaged in the activity. A child playing with Lego, for example, may be extremely serious about it (and not show much locomotor activity). An adult human playing a game of soccer may be extremely frustrated e.g. about being unable to perform properly or win. Nevertheless, it would be very strange if a scientist would come along telling people that such children playing with Lego and adults playing soccer are in fact not playing but ‘showing human-Lego/ball interaction behaviour’.
In this regard it may be relevant to note that most, if not all, of the leisure activities performed by young human children are considered play. In the case of growing and fattening pigs we may be tempted to believe that these animals are more or less adult because of their size. However, a finishing pig weighing 100 kg is, in fact, a very young animal, that has hardly reached its natural weaning age. So fattening pigs interacting with chains are very young animals too.
My most favourite comparisons are to compare chain play in pigs with human behaviour playing with a pencil or some other small object, and chewing gum. Adults may show these behaviours too. They may be repetitive, without being stereotypic (at least not in the sense of being indicative of substantially reduced welfare), and typically occur without any locomotor elements such as running, frolicking, gambolling or jumping about. Nevertheless, I my view such behaviours can properly be labelled as play, and similar behaviour in animals may be labelled similarly.

Voluntary or coerced, pleasure or frustration

Play is typically associated with positive welfare, with having fun and/or pleasurable emotions. Chain manipulation may be stereotyped, especially in tethered sows. This may or may not directly indicate negative affect (e.g. hunger or fixation stress). However, this does not imply that chain manipulation in younger pigs is similarly ‘abnormal’ or stereotyped. In fact, the manipulation of straw, the ‘ideal’ type of enrichment, may be at least as abnormal, as pigs would rarely be observed interacting with straw under natural conditions for long periods of time. Extensive straw manipulation under natural conditions would not be beneficial for pig survival. Furthermore, chain play in young pigs is rather voluntary as these pigs are typically fed ad libitum and kept in groups where the chain is hanging at a pen wall. Young pigs, therefore, can, it seems, easily ignore the chain if they would want to. Hence, it is likely that most of the interaction with the chain is motivated by the pigs wanting to interact with it, even though this, in my view, does not necessarily imply that their welfare is positive overall.


In this short communication I have tried to clarify the differences between the conventional use of the term ‘play’ in science and its use in ordinary language. I have argued that the classical scientific use, requiring behavioural variability, positive emotions and locomotor elements, may be too rigid and that there are good reasons to allow the word ‘play’ to be used for object-directed behaviour in the case of pigs playing with point-source objects like a metal chain, rope or plastic pipe. Pig farmers, suppliers and the public should be aware of the concerns scientists have in using the term play, as it may not always be associated with positive emotions and further research would be needed to establish more clearly if pig chain play classifies as play in the classical sense currently used in applied ethology.


Burghardt, G.M., 2005. The genesis of animal play: Testing the limits. MIT Press.
Wittgenstein, Ludwig (2001) [1953]. Philosophical Investigations. Blackwell Publishing.

Pig tail

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6 Responses to Do pigs play with chains? Science versus society

  1. Reviewer 1 says:

    I have made a few comments – as you can see I don’t really agree but then I am not sure I have the data to completely refute your case either.
    Ad Abstract:
    From Held and Spinka (2011): Burghardt’s (2005) five essential criteria work well for our purposes here. For him, play (1) is a behaviour that is not ‘fully functional’ (by this is meant it includes elements ‘that do not contribute to current survival’); (2) is ‘autotelic’, that is self-rewarding …; (3) differs in structure and/or timing from the adult, ‘serious’ form of the behaviour; (4) is performed ‘repeatedly’, but not stereotypically; and (5) is initiated when the animal is in a ‘relaxed field’ (by this is meant there are no immediate threats to the animal’s fitness). The main types of play are social play directed at a conspecifc (as in Burghardt 2005), locomotor-rotational (alone or in company, see Wilson & Kleiman 1974) and object play (see Fagen 1981); examples are given in Table 1 (cited from Held and Spinka, 2011).
    So the question is I think scientifically does interacting with a chain meet these specifications – in truth I suspect that we don’t exactly know because we have never ‘tested’ how pigs interact with chains against these 5 criteria – accepting that they are quite loose and difficult to test against – also you have to take account of the clear link to positive emotional state in these criteria (see below).
    Ad Introduction: Hence, besides locomotor and object play, there is also social play and in pigs these are often intermingled.
    Ad Neutral terms: “This preference may derive both from a need to be able to measure/operationalise the term and from a reluctance to imply the presence of emotions”.
    See above which refers to play being rewarding and animals playing when they are relaxed – there is a lot of data to support that play is inhibited by negative factors.
    Ad Different meanings of words used in science and common language:
    “But in the case of object play, there doesn’t seem to be a need for a divergence between science and ordinary language, if we could agree to use the word to refer unambiguously to the object-directed behaviour that is being observed.”
    Well I think I might disagree – the Burghardt criteria do encompass positive emotional state.
    Ad Exploration as underlying motivation:
    I found this paragraph a bit confusing.
    “Scientists tend to classify object play as a form of exploratory behaviour. But is this correct?”
    Actually I think it is seen as something a bit different to exploration which does not have the characteristics outlined by Burghardt.
    Ad Variability and locomotion:
    “It may be questioned, however, if it is necessary for object play in particular to be variable, developmental and involve locomotor elements like running, twisting and play fighting.”
    You could say that but I think you are running against a tide of thinking and evidence that makes play a distinct developmental phenomenon.
    Ad Human play:
    “Playing a game of chess would be a typical example.”
    Chess rarely meets Burgdorfs criteria (only when young children play it! – which sort of makes the point that developmental play is distinct from the wider use of the term.
    “Nevertheless, it would be very strange if a scientist would come along telling people that children playing with Lego are in fact not playing but ‘showing human-Lego interaction behaviour’.”
    Human juvenile play does have ‘mental fantasy’ aspects which are distinct probably to animal play.
    Ad Conclusions:
    It is not possible to wholly refute what you say because we have probably not tested chain behaviour against the play criteria – however I suspect it would fall short – also I feel that some of what you have written here does not take account of the wider literature – e.g. on human play – see above (Pellegrini and Smith, 1998).
    Cf also: “Exploration is goaldirected information gathering, whereas in play children are not concerned with an end product (Wohlwill,1984).” (cited from Pellegrini and Smith, 1998)).

    Held S.D.E. and Spinka, M. 2011. Animal play and animal welfare. Animal Behaviour 81: 891-899.
    Pellegrini, A.D and Smith, P.K. 1998. Physical Activity Play: Consensus and Debate. Child Development, 69: 609-610.

    • Marc says:

      As to social play and overlap: In my, nonclassical, perception there is locomotor play which often involves locomotion in a social context, but which may also be object directed, e.g. running around a tree or up some kind of elevation. Locomotor play may also occur with an object (as in the case of animal-‘soccer’), but by contrast there is also more static object play that typically does not involved running or jumping about. It is that kind of static object play that this blog is about.
      As to the Burghardt (2005) criteria I see no hard conflict with labelling chain manipulation as play. The same goes for human pencil manipulation/play and chewing gum.
      As to Pellegrini and Smith “in play children are not concerned with an end product”. I think that is extremely divergent from common usage of the term. Children playing with Lego or playing soccer are very much concerned with an end state (as perceived by them), in my view.

  2. Reviewer 2 says:

    I have to say that when it comes to terms I prefer being strict (even though I am surely not very good at always being so myself), especially if there is a risk that ‘incorrect’ use of a word might lead to things being wrongly interpretated or simplified …. Thus, I have to say I agree … that the term ‘play’ should be restricted to behaviours we know are linked to positive emotions, and other previously defined aspects, and if we can not be sure, it is better to use a more objective term. And I actually do not really understand why you think it is necessary to use the word play for chain manipulation, when the latter is very easy to understand too, independent on who the focus group is?

    • Marc says:

      I don not think it is necessary to use the word play for chain manipulation. I’m arguing it should be allowed, following normal rules and conventions in common language as well as in science. In my view the current restrictive use in science is unnecessarily restrictive, and could be relaxed, without eliminating the desire to investigate the various components and functions of play (like association with positive emotions and developmental function).

  3. Reviewer 3 says:

    I also strongly support that a scientist should use terminology correct.
    You state ‘This blog challenges the scientific use of the word play’.
    But throughout the text you use the term object play to refer to chain manipulation, even before you present your argument.
    You insist that chain manipulation is object play, but I do not see the challenge.
    I think you are leaving out a lot and I do not find the text very informative.
    You do not consider the 5 criteria defining animal play behaviour.
    You draw parallels to children play without considering the special types of play in humans.
    You do not consider exploratory behaviour.
    If you wish to challenge the scientific terminology, should the reader not know what you are challenging?
    Reading your text I was wondering whether the aim of your text might be: to provide a scientific ‘challenge’, or to challenge science?

    • Marc says:

      I changed ‘chain play’ a number of times to ‘chain manipulation’.
      I’m reluctant to attribute special mental cognitive functions to human play. I wouldn’t deny there may be differences, but I’m most reluctant to presuppose such differences because of our historical inclination to reserve a special place for our own species without it necessarily being justified (cf Frans de Waal, 2016. Are We Smart Enough to Know How Smart Animals Are? Norton.
      I’ve been challenging the restrictive use of the term play in applied ethology, and I agree that this challenge would benefit from stimulating challenging scientific research as well (so that is what I have added in the text).

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