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Pigs as Laboratory Animals
Jeremy N. Marchant-Forde and Mette S. Herskin
Abbreviations used:
3 Rs: the guiding principles for more ethical use of animals in testing which include replacement
(methods which replace the use of animals), reduction (methods which reduce the number of
animals used) and refinement (methods which refine animal welfare and reduce suffering)
NCE (new chemical entity): is a molecule developed in the early drug discovery stage, which after
undergoing clinical trials could translate into a drug that could be a treatment for some disease
NSAID (non steroidal anti-inflammatory drug): a class of drugs that provide analgesic (pain-killing)
and antipyretic (fever-reducing) effects, and, in higher doses, anti-inflammatory effects. Used in
human (Aspirin, Ibuprofen, Paracetamol) as well as veterinary medicine.
Abstract
The pig is increasingly popular as a laboratory animal either as the target species in its own right or as
a model for humans in biomedical science. As an intelligent, social animal it has a complex behavioral
repertoire reminiscent of its ancestor, the wild boar. Within a laboratory setting, the pig may be the
subject to a variety of invasive and non-invasive experimental procedures which may have short-
and/or long-term impacts on its welfare. Ordinarily, pigs kept as laboratory animals will come under
regulations or legislation governing use as lab animals rather than farm animals and be subject to
increased individual monitoring as a result, even though there may be a lack of species-specific
protocols to assess the welfare of laboratory pigs. A major issue with laboratory animals is pain and
its management. Again, there is a lack of validated methodology to monitor and document pain in
the laboratory pig, although there are some recommendations available regarding the use of NSAIDs
as analgesics. Within a laboratory setting, pigs may be subject to housing that is sub-optimal in terms
of their needs, with the emphasis on hygiene and needs of the caretaker. Environments may be
barren and uncomfortable, and the pig may be socially isolated. However, the environment can be
modified to improve the pig’s welfare, without forfeiting human requirements. Feed can be supplied
in a way that reduces hunger, reduces excessive weight gain and reduces aggression where pigs are
group-housed. Laboratory pigs are subject to more frequent human interaction than farm pigs and
there is the opportunity for the human to improve the pig’s welfare by avoiding negative handling
and by implementing positive reinforcement techniques to train pigs to undergo aspects of
experimental procedures, thereby minimizing stress. At present, there is little scientific literature on
laboratory pig welfare and although there is relevant information that can be transferred from pigs
kept as farm animals, more research is needed to fill gaps in the knowledge and validate measures of
welfare for application in laboratory settings.
1. Introduction
The majority of this book has focused on the pig as a meat-producing animal. In this chapter, we
argue that the pig is indeed unique, because of a combined use for meat production as well as for
research, which is not normally seen in domestic animals. The pig, however, shares large anatomical
and physiological homologies with humans, which have driven the increasing use of this animal
species as an animal model (Swindle and Smith, 2015). Today, the pig is recognized as an
advantageous non-rodent animal model within a large number of biomedical research areas (as
reviewed by Roth and Tuggle (2015)). In addition, the pig is the leading animal species within studies
of xenotransplantation of animal organs into humans (Schook et al., 2005). Across these multiple
research areas, the size similarity between pigs and man is a clear advantage (Søndergaard and
Herskin, 2012), allowing the use of human devices combined with access to relatively large volumes
of body fluids and tissue (Nunoya et al., 2007).
Compared to the traditional laboratory rodents, the main biomedical purpose of which are to model
human conditions, the important role of the pig as meat-producing animal, means that pigs are also
subject of research in their own rights – for example in studies of porcine nutrition (Lærke et al.,
2015), diseases (Mustonen et al., 2012) or housing (as surveyed by Ganderup, 2015). Even though all
these research areas share the use of pigs, it is important to emphasize that a large number of pig
breeds are available and used for research, each with distinct characteristics, and highly variable
body sizes – from micro pigs to the traditional farmed breeds (as reviewed by McCrackin and Swindle
(2015) and Ganderup (2015)).
As discussed in the earlier chapters of this book, the welfare of the large breeds of pigs kept as meat-
producing animals, have received scientific as well as public attention for decades (Pedersen,
Chapter 4, this volume), and at present international as well as national legal requirements aim to
ensure pig welfare. More recently, a number of technical guidelines and health-care programs for the
management of swine in research have been published (Bollen et al., 2000; Laber et al., 2002).
However, as discussed by Søndergaard et al. (2011), the level of reporting on welfare of laboratory
pigs in biomedical studies have been strikingly low. In this chapter, we aim to combine knowledge
from studies of farmed as well as laboratory pigs in a discussion of central aspects of pig welfare
considered relevant for pigs kept for research purposes.
2. Monitoring of laboratory pig welfare
Using animals for experimental purposes, one has legal, ethical as well as scientific responsibilities to
ensure and document the welfare standard for the concerned individuals – for the sake of the pigs,
but inasmuch due to the potential effects of the animal welfare state on the scientific outcomes. In
many regions of the world, experimental animals maintain special legal protection (as compared to
animals kept for food or companion animals). One such example is the obligation for animal studies
to undergo ethical review including justification of the expected aims, documentation of the severity
of the planned procedures, and establishment of humane endpoints. The latter constitute pre-
determined clinical criteria for the exclusion of animals from studies (most often followed by
immediate euthanasia), in order to limit suffering. Additionally, in many regions of the world,
researchers have a legal requirement to comply with the 3Rs (as originally proposed by Russell and
Burch, 1959), aiming to replace the use of live animals as much as possible, reduce the number of
animals used, and – more relevant for this chapter – to refine the techniques and procedures
involving animals as much as possible, in order to minimize the welfare burden for the animals.
Without questioning the original intentions underlying the 3Rs, we would, however, like to draw the
attention to more recent publications discussing relations between the 3Rs and animal welfare (such
as Rusche (2003) or Olsson et al. (2012)).
In order to perform animal experiments in compliance with the mentioned requirements, the welfare
of the experimental animals must be monitored. Within the field of biomedicine, The Federation of
European Laboratory Animal Science Associations (FELASA) has issued guidelines on how to monitor
health of pigs (Rehbinder et al., 1998). However, less attention has been given to other aspects of
porcine welfare. In fact, as discussed by Søndergaard et al. (2011), at present no validated welfare
monitoring tools have been published for laboratory pigs, and in the majority of the recent papers
presenting results from in vivo porcine studies, no such monitoring have been described. Taking the
large focus on welfare of pigs kept as meat-producing animals, and the availability of welfare scoring
systems for pigs kept for these purposes (e.g., Welfare Quality (2009) which involves animal- as well
as resource-based measures), into account, such lack of validated protocols for monitoring of the
welfare of laboratory pigs is surprising.
For legislative purposes, there is often a focus on “input” resource-based measures – i.e.
measurement of physical resources that should be provided to the animal in order to safeguard its
welfare, rather than “output” animal-based measures – i.e. direct measures of the animal’s behavior
or health, etc. (Main et al., 2007). Although more recently there has been the development of
assessment protocols that focus more on animal-based measures, such as the Welfare Quality ones,
they still have some limitations in on-farm settings, due to the sheer number of animals on a given
farm and the time required to carry them out. In the laboratory setting, where numbers of animals
and caretakers are shifted much more towards the individual animal, the monitoring of the welfare
of individuals should be more simple to achieve. There are examples of studies reporting the
development of porcine perioperative care based on series of cases (Murison et al., 2009), as well as
recommendations for postoperative monitoring during the anesthetic phase and in the hours after
anesthesia (Swindle and Sitino, 2015). For longer-term studies, Swindle and Sitino (2015) recommend
development of study specific monitoring tools involving clinical and behavioural indicators in order
to determine the welfare state of the animals throughout a study period. As health and welfare are
entangled concepts (Broom, 2006), it is important to state, that a systematic assessment of animal
welfare necessitates knowledge about, and ability to interpret, the biology of the involved animal
species, its species-specific behaviour and clinical symptoms.
One suggested basis for such development of a welfare monitoring tool, could be a combination of,
and re-development of, the welfare indicators validated for farmed pigs (where focus is often put at
pen level (e.g. Welfare Quality, 2009)) and clinical health indicators used in studies of toxicology
(Helke, 2015) or clinical studies of pigs after experimental infection (Mustonen et al., 2012). It is
important to emphasize that even though, traditionally and legally, it is accepted that healthy pigs
kept for meat production are checked by the farmer once per day, laboratory pigs may need scoring
of their conditions at considerably higher frequencies. As discussed by Murison et al. (2009) for
airway research, an appropriate welfare monitoring tool must be adapted to the specific
experimental conditions bearing in mind that the range of research areas involving pigs, covers
different potential challenges to animal welfare such as tissue damage or type of housing, each of
which can be graded from mild to severe. As an example, tissue damage may be graded from mild
(such as being exposed to UVB-light (Di Giminiani et al., 2014)) to moderate (such a tail docking as
part of research into husbandry procedures (Marchant-Forde et al., 2009)) or even severe (such as
spinal cord injury (Navarro et al., 2012)). Recently, Olsen et al. (2016) used the pre-formulated
humane endpoints to conclude that they could not justify further use of a conscious porcine model
of severe sepsis. The fact that the pig is often considered robust to welfare challenges (as proposed
by Navarro et al., 2012) means that welfare indicators such a death or decreased growth should not
stand alone, but must be supported by more sensitive clinical, behavioural and resource-based
indicators in order to achieve a tool of appropriate sensitivity. The literature covering the welfare of
pigs as meat-producing animals carries many examples of potential welfare indicator candidates,
which are also relevant for pigs kept as laboratory animals, including animal-, management- and
ressource-based indicators. Hence, a future scientific development and validation of a welfare
monitoring tool for pigs used in research, should take the available knowledge from farmed pigs into
account.
3. Welfare and Housing
Housing for the laboratory pig often meets the concept of traditional laboratory animal housing, i.e.
housing that is sterile, isolated, easy to manage, environmentally-controlled and built for the specific
needs of the caretaker and for the procedures which the pig will undergo (see Figure 1).
Figure 1: Example of raised floor housing pens for laboratory pigs. (Sources: www.altdesign.com,
www.lenderking.com)
There is also the long-running belief that for laboratory animal studies to be reproducible there
should be environmental standardization and that this is best achieved by having homogenous
housing conditions. As we now know, such standardization can actually be detrimental to
reproducibility (Richter et al., 2009) and that systematic variation of environmental conditions such
as enrichment, enclosure size, sound and lighting, can actually be beneficial (Richter et al., 2010).
Handbooks on the care of laboratory pigs vary in the amount of detail given about housing
requirements dependent on whether they are written by industry bodies or NGOs concerned with
the welfare of laboratory animals. For example, the National Research Council of the National
Academies’ Guide for the Care and Use of Laboratory Animals (ILAR, 2011) contains much use of the
terms ‘adequate’ and ‘appropriate’ in its descriptions of the animal’s microenvironment being only
specific for pigs in documenting minimum space requirements and that they should be provided with
manipulable toys.
Other handbooks or guides (e.g., Holtz, 2010; RSPCA, 2011; Skoumbourdis, 2015) contain more detail,
giving an outline of the pig’s nature and how it applies to the design of housing and management
systems that will safeguard its welfare, such as social living, thermal and physical comfort and
stimulating enrichment. This section will cover how the environment of the laboratory pig may
impact its welfare.
a. Comfort, sterility and hygiene
The thermal and physical comfort of the laboratory pig can be greatly influenced by elements of the
environment, such as flooring, bedding substrates and social housing. The Guide for the Care and
Use of Laboratory Animals (ILAR, 2011) describes an enclosure that “should be made of durable,
nontoxic materials” and that “flooring should be solid, perforated, or slatted with a slip-resistant
surface.” Many of the purpose-built laboratory pig housing pens (see Figure 1) combine fully-slatted
flooring with solid metal sides, clearly designed to meet the care-takers needs rather than the pigs.
If housed individually in such pens, it is crucially important that the thermal environment of the room
falls within the thermoneutral zone of the pig, given its age and size, as there is little ability for the
pig to regulate its own thermal comfort, by wallowing or huddling. Both heat stress (Muns et al.,
2016a) and cold stress (Muns et al., 2016b) can, due to the fact that pigs lack sweat glands and
consequently need to thermoregulate behaviourally (Ingram, 1965) - have large welfare implications
for pigs, resulting in physiological and behavioral changes and increased morbidity and mortality.
Building in design elements that allow the pig a choice in thermal environment will improve welfare.
This could be achieved by either providing zones with differing temperatures – pigs will choose
temperatures that are more comfortable (Vasdal et al., 2010) - or by maintaining temperature and
offering choice in floor substrate. Day-old piglets kept at a constant 34°C preferred sawdust on a
solid floor over either foam or water-filled mattress (Vasdal et al., 2010), whereas older pigs (3-4
months old) kept at 18°C preferred sawdust on a solid floor over solid or slatted concrete, but when
the temperature was raised to 27°C, the preference reversed and the non-bedded floor was
preferred (Ducreux et al., 2002). The importance for the pig to have a degree of ability to control its
thermal environment can be illustrated by the classic experiments detailed by Baldwin (1979). When
trained to operate radiant heaters by pressing a panel switch, pigs will activate the heater, with the
amount of use influenced by such things as environmental temperature and metabolic heat
production as a result of feed intake.
Bedding or flooring type may not only confer advantages in terms of thermal comfort, but can also
offer physical comfort and be a source of environmental enrichment (see below). Hard flooring is
known as a risk factor for physical injuries such as decubital shoulder ulcers (Herskin et al., 2011), claw
lesions (Jensen & Toft, 2009) and fore-limb skin abrasions (Mouttotou et al., 1999). Adding a bedding
substrate such as straw, shavings or sawdust can improve the comfort of the pig. Although there are
hygiene concerns when using organic material such as straw for bedding leading to an increase in
some illnesses (see discussion in Tuyttens, 2005), there is also strong evidence that straw especially
can decrease prevalence of other conditions, such as leg and hoof injuries (Andersen and Bøe, 1999),
influenza (Ewald et al., 1994), tail-biting (Van de Weerd et al.( 2005); see also Valros, Chapter 7, this
volume) and gastro-intestinal disorders, including stomach ulcers (Herskin et al., 2016).
However, the addition of organic bedding increases cost and labor requirements and requires the
regular introduction of external material into what may be a bio-secure environment. An alternative
could be the use of rubber or plastic-coated foam matting. Within commercial pig production, mats
have been shown to improve the comfort of gestating sows (Tuyttens et al., 2008, Elmore et al.,
2010), farrowing sows (Boyle et al., 2000), finishing pigs (Savary et al., 2011) and pre-weaned piglets
(Gu et al., 2010), with the added advantage over fully-slatted steel flooring of demonstrated reduced
diarrhea morbidity in the piglet study (Gu et al., 2010). Within a laboratory pig setting, mats have
been shown to be preferred compared to slatted flooring (DeBoer et al., 2013) and when combined
with a mirror, to reduce plasma cortisol concentrations and other measures of stress or poor welfare
when compared with pigs housed with neither mat nor mirror (DeBoer et al., 2015).
b. Barren environments and environmental enrichment
Ideally, the laboratory pig will be housed in a complex environment with access to space,
companions, bedding, rooting material, unrestricted food and water, vegetation, a wallow, etc.
However, the reality is that the traditional laboratory pig environment is a barren environment,
meeting the needs of the caretaker, rather than the needs of the pig, as illustrated in Figure 1. As
such, much of the focus within a laboratory setting will be on point-source enrichment – that is
enrichment objects or racks/dispensers that are generally size-limited and presented in a given
location within the pen, although all effort should be made to incorporate bedding.
Keeping animals in barren environments can lead to behavioral problems, boredom and poor
welfare, but these issues can be ameliorated by the use of environmental enrichment. Environmental
enrichment can be defined as “an improvement in the biological functioning of captive animals
resulting from modifications to their environment” (Newberry, 1995). The key part of this definition
is the improvement in biological functioning. The addition of any complexity into a barren
environment does not necessarily improve it, and complexity must be reviewed in terms of biological
relevance to the animal and its ability to improve the animal’s quality of life.
Würbel and Garner (2007) classify enrichments into 3 classes: pseudo-enrichments (“never
biologically relevant, and either neutral or even detrimental to animal welfare”), conditionally-
beneficial enrichments (“biologically relevant, but may induce welfare problems if not properly
managed”), and beneficial enrichments (“biologically relevant, beneficial to animal welfare, and
rarely if ever associated with welfare problems”). Although the paper is focused on laboratory
rodents, the principles hold true for laboratory pigs. As an example of pseudo-enrichment, adding
marbles to a rodent’s cage, rather than improving welfare, actually induces stress (De Boer and
Koolhaas, 2003) and the rodents will bury the marbles to remove the stressor (defensive burying). As
an example of conditionally-beneficial enrichment, adding shelters to cages for male mice may result
in the introduction of a defendable resource that can increase aggression (Nevison et al., 1999).
Nesting material is a beneficial enrichment.
So for the pig, what constitutes a beneficial enrichment? What is biologically relevant to the pig,
beneficial to the pig’s welfare and rarely, if ever, associated with welfare problems? The natural
behaviour of the pig has been covered in detail elsewhere (D’Eath and Turner, 2009), but in
summary, we have a woodland-dwelling, social animal that spends a large amount of its time
foraging, using its snout and mouth to investigate. The pig has an extensive behavioral repertoire,
and its primary sense is olfaction. It establishes stable family groups, which are hierarchical, avoiding
unfamiliar pigs and accessing resources based on social status, which is reinforced without overt
aggression. For an enrichment to be relevant, it needs to have properties that allows a pig to
“express key elements of its behavioural repertoire” (van de Weerd et al., 2003), and much of the
focus with pigs has been on items that address its foraging and exploratory nature.
Within the European Union, the issue of environmental enrichment in commercial pig production has
received a large amount of attention due to its relationship with tail-biting and the desired intent to
eradicate the painful procedure of tail docking (Valros, Chapter 7, this volume). A full scientific report
on these interacting issues is available (EFSA AHAW Panel, 2014) and the contents of a Commission
Staff Working Document (EU, 2016a) has been formulated into a Commission Recommendation (EU
2016/336) which gives detail on what constitutes good environmental enrichment for pigs (EU
2016b):
“4. Enrichment materials should enable pigs to fulfil their essential needs without compromising
their health. For that purpose, enrichment materials should be safe and have the following
characteristics:
(a) Edible — so that pigs can eat or smell them, preferably with some nutritional benefits;
(b) Chewable — so that pigs can bite them;
(c) Investigable — so that pigs can investigate them;
(d) Manipulable — so that pigs can change their location, appearance or structure.
5. In addition to the characteristics listed in paragraph 4, enrichment materials should be provided in
such a way that they are:
(a) of sustainable interest, that is to say, they should encourage the exploratory behaviour of
pigs and be regularly replaced and replenished;
(b) accessible for oral manipulation;
(c) given in sufficient quantity;
(d) clean and hygienic.
6. In order to fulfil pigs' essential needs enrichments material should meet all the characteristics
listed in paragraphs 4 and 5. To that end, enrichments materials should be categorised as:
(a) optimal materials — materials possessing all the characteristics listed in paragraphs 4 and
5 and therefore such materials can be used alone;
(b) suboptimal materials — materials possessing most of the characteristics listed in
paragraphs 4 and 5 and therefore such materials should be used in combination with other
materials;
(c) materials of marginal interest — materials providing distraction for pigs which should not
be considered as fulfilling their essential needs and therefore optimal or suboptimal
materials should also be provided.”
Many of the ‘enrichment’ items sold by laboratory animal equipment retailers often address only one
or two of the key characteristics in that they are chewable and/or investigable (Figure 2). They will
get some interest from pigs when added to a barren environment but that interest will decrease
over time as the novelty wears off (e.g. see Smith et al., 2009) and as such would qualify only as
marginal enrichments, as set out in Table 1 taken from the Commission Staff Working Document (EU,
2016a).
Figure 2: Examples of traditional enrichment items sold by laboratory animal equipment
manufacturers.
(Sources: www.labsupplytx.com, www.ottoenvironmental.com, www.animalspecialties.biz )
Table 1: Possible enrichment materials used for pigs and their interest as enrichment material
Materials
Provided as
Level of
interest as
enrichment
materials
May be complemented by…
Straw, hay, silage,
miscanthus, root vegetables
Bedding
Optimal
Can be used alone
Soil
Bedding
Suboptimal
Edible and chewable materials
Wood shaving
Bedding
Suboptimal
Edible and manipulable materials
Sawdust
Bedding
Suboptimal
Edible, chewable materials
Mushroom compost, peat
Bedding
Suboptimal
Edible materials
Sand and stones
Bedding
Suboptimal
Edible and chewable materials
Shredded paper
Partial bedding
Suboptimal
Edible materials
Pellet dispenser
Dispenser
Suboptimal
Depending on the amount of
pellets provided
Straw, hay or silage
Rack feed or in
dispenser
Suboptimal
Investigable and manipulable
materials
Soft, untreated wood, card-
board, natural rope, hessian
sack
Object
Suboptimal
Edible and investigable materials
Compressed straw in
cylinder
Object
Suboptimal
Investigable and manipulable
materials
Sawdust briquette
(suspended or fixed)
Object
Suboptimal
Edible, investigable and
manipulable materials
Chain, rubber, soft plastic
pipes, hard plastic, hard
wood, ball, salt lick
Object
Marginal
Should be completed by optimal
or suboptimal materials
This list is not exhaustive and the materials are not ranked. Other materials may be used provided
they meet legal requirements
The fact that laboratory pigs are usually housed in much smaller numbers than commercial pigs does
have advantages. The number of options that are practical to employ is greater and as pigs may be
housed individually or in very small groups, the risk of the enrichment becoming a defendable
resource is decreased. Some examples of enrichment objects known to have value in commercial
settings include wood and straw racks (Telkanranta et al., 2014 – Figure 3a) and the EasyFix™ toy
(O’Driscoll 2015 - Figure 3b). Another option may be the placement of a snout-operated pellet
dispenser (Figure 3c), which can be made by cutting a 30 to 60 cm section of PVC pipe, adding cap
ends and drilling 2cm holes throughout PVC. The pipe is then filled with treats and can be left on the
floor or mounted on the wall in a way to enable the pipe to rotate. Pigs will have to root and turn the
pipe to allow the treats to fall out.
Figure 3: Examples of enrichment items used in commercial husbandry or small-scale/companion pig
rearing.
(Sources: www.telkanranta.com, www.farewelldock.eu, www.minipiginfo.com)
In general, there is little research available on enrichment for pigs specifically housed as laboratory
animals. There are good guidelines for enrichment for pigs housed in commercial settings, and much
of this is directly applicable and transferable. However, the enrichment of perhaps tens of thousands
of pigs on a single commercial farm poses very different challenges to the enrichment of a few pigs
a)
b)
c)
in a laboratory setting and there are opportunities for further development of enrichment which may
only be practical in the laboratory setting. An example of this is the use of separate pens to become
a designated ‘playroom’ through which pigs can be rotated for specific periods of time (Casey et al.,
2007).
c. Social housing and social isolation
Naturally, the pig is a social animal (D’Eath and Turner, 2009), living its life in a related, usually multi-
aged, stable group, with the exception of mature boars which make only short-term associations
with other individuals independent of kin (Podgórski et al., 2014). Given the pig’s natural history,
keeping pigs in commercial farming and laboratory settings poses some challenges. Within the
laboratory setting, pigs may be relatively long-term residents and during this time may undergo
repeated disruption of stable groups and also periods of isolation. Both of these social stressors can
result in physiological and behavioural indicators of stress, impacting the animal’s welfare and,
potentially, health (see review by Proudfoot and Habing, 2015).
The formation of groups of pigs, and especially sows, has attracted a great deal of research in the
commercial sector, given that the establishment of the social hierarchy results in aggression, which
can be sustained if the environment is suboptimal. Detailed reviews of methods to ameliorate
aggression at mixing are available elsewhere (Marchant-Forde and Marchant-Forde, 2005; Marchant-
Forde, 2009; Spoolder et al., 2009; Verdon et al., 2015). Factors that can minimize aggression include:
1) pen designs that incorporate lots of space and, if possible, get-away areas or barriers behind which
pigs can retreat, and 2) management techniques such as provision of food ad libitum around mixing,
mixing in the presence of a super-dominant animal, pre-exposing pigs to each other by penning in
adjacent pens which allow communication, and allowing litters to mix as piglets to build social skills.
Aggression at mixing cannot be eradicated, but once the hierarchy is established, and this takes a
matter of hours only, overt aggression should be seen only occasionally. Aggression does impact
welfare, especially in those individuals subject to high levels of social defeat, and may result in, for
example, injury, activated HPA axis, decreased immunity and increased morbidity (see also Verdon
and Rault, Chapter 9, this volume).
Recommendations for laboratory pigs are, wherever possible, to house pigs in groups or pairs (Holtz,
2010; ILAR, 2011; RSPCA, 2011; Skoumbourdis, 2015) and the importance of social support cannot be
understated (Rault 2012). In his review, Rault (2012) notes that the presence of a companion can
increase the incidence of behavioral indicators that demonstrate the attenuation of fear and distress,
and that animals exposed to stressors will actively seek company if it is available. When housed in
pairs or groups, less distress vocalizations are emitted and the HPA axis shows reduced activation
following exposure to stressor. Additionally, social support may result in reduced blood pressure and
there is some evidence of modulated immune system function (reviewed in Rault, 2012).
Although social housing is preferred, there will be studies and procedures in the laboratory setting
that requires the pig to be housed individually. For example, pigs that have undergone implantation
of catheters or access ports will need to be housed alone to prevent pen-mates from damaging both
the implant and the host pig (see Figure 4). When housed individually, the extent to which this may
impact the welfare of the pig can be influenced by the design of the pen.
Figure 4: A laboratory pig fitted with a permanent T-shaped cannula in the ileum. (Source: Helle
Nygaard Lærke, Aarhus University)
Complete isolation for even a short period of time in young pigs can result in neuroendocrine and
behavioral changes that indicate increased arousal and distress (Kanitz et al., 2009). Furthermore,
social isolation can impact the expression of genes involved in regulation of neuronal function,
development and protection (Poletto et al., 2006) and lead to long-term changes in HPA activity
(Kanitz et al., 2004). The impacts of isolation on laboratory pigs have not been well-studied, but
there are some studies which indicate that different degrees of isolation result in different stress
states. A study that compared behaviour of either fully- or partially-isolated pigs with group housed
pigs, found that both isolation treatments showed an initial increase is behavioural indicators of
stress, such as pawing and escape attempts and reduced play (Herskin and Jensen, 2000). After 2
weeks, those in partial isolation – separated from other pigs by wire mesh only – were still showing
reduced play, but other indicators had waned, whereas those that were fully isolated – housed
across the room and but able to see the other pigs – were showing further increased pawing and
further reduced play. Both isolation treatments resulted in lower reactivity in a novel environment
test, with reduced locomotion and reduced vocalization, compared with group-housed pigs. Using a
similar experimental set-up minus the group housing treatment, and combining isolation
with/without surgical catheterization, Herskin and Hedemann (2001) found that partial isolation
resulted in increased activity and increased play compared with full isolation, indicating that the
provision of limited social contact may help reduce the negative effects of individual housing.
Experiments carried out by DeBoer et al. (2013; 2015) also highlight the degree to which physical
isolation impacts behavior and welfare. In the first study (DeBoer et al., 2013), individually-housed
pigs were able to move between four connected, woven-wire-floored pens, each of which were
slightly different. One was a control pen with four solid sides. One had a mirror and three solid sides
(Figure 5a). One had four solid sides and a rubber mat. One had an open side which allowed the pig
to see a companion pig across the corridor. Undisturbed, the pigs chose to spend more time in the
pen opposite the companion and less time in the control pen, with the other two treatments
intermediate. However, when a human entered the room, the amount of time spent in a pen with a
social enrichment (i.e. across from the companion or with the mirror) was far greater than time
spent in the other two pens, and there was no preference for companion over mirror. These results
suggest that a mirror may be used by the animal for social support during periods of perceived
threat. In a follow-up study, the mirror and mat were combined as an enrichment for a specialized
housing system (The PigTurn® - Figure 5b) which was examined in combination with isolation
treatments – either visually isolated (but within the same room) or still physically isolated but able to
see other pigs. The results showed that enrichment given to pigs housed in visual isolation had no
effect on plasma cortisol concentrations, but greatly reduced it in the pigs able to see other pigs.
Other measures suggested that in the absence of enrichment, being able to see other pigs but not
physically interact was frustrating. Appropriate enrichment and proximity of another pig improved
welfare. Wherever possible, tactile communication, even through mesh walls, should be practiced
and mirrors used where this is not available.
Figure 5: a) A laboratory pig undergoing choice testing including a pen with a mirror, and b) within a
PigTurn® pen enriched using a mirror and a rubber mat. (Source: Shelly Pfeffer DeBoer)
4. Welfare and Feeding
a. Dietary content
The nutritional requirements of all pigs are covered in detail within the NRC (2012) guidelines, which
sets out the best estimates for minimum requirements for such constituents as proteins, minerals
and vitamins and recommended energy levels and quantity of feed to be given to pigs of different
age groups. Some of the summarized data are shown in Table 2. These data relate to growing farm
pigs being fed to maximize growth, and gestating sows in the 220-250kg bodyweight range being fed
to support pregnancy and maintain bodyweight and body condition.
Table 2: Dietary Requirements of Growing Pigs Allowed Feed Ad Libitum (90% dry matter) and
restricted fed gestating sows.
Weight range of pig
(kg)
ME content of diet
(kcal/kg)
Estimated feed intake
(g/day)
Crude protein (%)
5-7
3400
280
24-26
7-11
3400
500
22-24
11-25
3350
950
21-25
25-50
3300
1600
19.3
50-75
3300
2230
17.1
a)
b)
75-100
3300
2640
15.2
100-135
3300
2950
13.4
Gestating sows
3265
2000
12.2
Data adapted from NRC 2012
From a laboratory pig viewpoint, the aim is not to maximize growth rates and therefore, there must
be some dietary adjustment in either content or quantity in order to maintain pigs at the size and
body condition required over the projected time period that they are needed. From a content aspect,
the most common changes in lab pig diets compared to farm pig diets are reductions in energy and
protein content and an increase in crude fibre content. For example, a typical farm pig starter diet
might be expected to have 3500 kcal/kg ME, 24% crude protein and 2.5-3% crude fibre, whereas a
laboratory pig starter diet might be 3200 kcal/kg ME, 21% CP and 4% fibre. Increasing fibre content is
an often-used mechanism to restrict energy intake yet maintain satiety, thereby facilitating normal
behaviour (e.g. Sapkota et al., 2016). However, it must also be noted that high fiber content (15%
plus) in diets may lengthen gastric emptying and intestinal transit time (Bollen et al., 2000) with
subsequent impact on digestion and, potentially, digestive physiology.
b. Diet availability – restriction/ad lib feeding
As ad libitum feeding of conventional and energy-reduced diets can lead to obesity in pigs kept for
laboratory purposes, quantitative reduction is achieved by restricted feeding, that is giving the pig
access to a limited amount of food, once or twice a day. Without ad libitum access, the pig will be
hungry for at least part of each day, which is a welfare issue. The implications of food restriction and
hunger are well covered elsewhere (D’Eath et al., 2009; D’Eath et al., Chapter 10, this volume), but
for the pig, which is a natural forager, having limited access to food can affect its daily time budget
both in terms of amounts and types of behaviors performed. If food is not going to be available all
the time, then as discussed in Section 3.b, the environment needs sufficient complexity to enable the
pig to fill its time with foraging-like behaviour that will encompass substrate-directed manipulation.
Without this, there is a risk of increased pen-mate-directed manipulation or development of
stereotypic behaviours, both of which are indicators of poor welfare.
c. Feeding system
For pigs kept in groups, a major housing factor that impacts their welfare is that of feeding system
design. If food is available ad libitum, pigs can choose when to eat and avoid conflict. Ad lib delivery
of a high fibre/low energy diet is a good method to reduce food-related aggression and hunger in
slow-growing lab pigs or minipigs, but for commercial pigs used for laboratory purposes, growth
may need to be controlled by restricted feeding. Where food is limited, its importance as a resource
is heightened and it becomes a source of competition, which can be influenced by the way the food
is delivered. Floor feeding is the simplest system but can result in high levels of aggression and it is
possible for the dominant pig to monopolize the food, resulting in variable individual feed intake.
Trough feeding can help spread out the food source allowing all pigs to access the food
simultaneously if there is sufficient trough space per pig. Barriers along the trough can help to give
separate feeding places and liquid feeding can equalize eating speed, and reduce the chance of a
quick eater displacing slower eaters. Other systems used with farm pigs include feeding stalls into
which individuals can be shut and electronic feeder systems, in which pigs feed sequentially. Both
these types of systems have the advantage for the carer of being able to deliver different amounts
to individuals based on body condition or individual needs. The relative advantages and
disadvantages of feeding systems are discussed in more detail elsewhere (Marchant-Forde, 2009;
Verdon & Rault – Chapter 9, this volume). For laboratory pigs housed individually, the issues with
competition do not apply, and a simple, single-space feeder is appropriate. For studies on obesity,
metabolic processes and others where monitoring of appetite and feed intake may be important,
there is also the option to have feeding systems that can record meal durations and amount of food
consumed. Various options are available commercially (e.g. the MP Feed Intake Monitoring system,
MBRose, Faaborg, DK – see Figure 6) for either individually- or group-housed pigs.
Figure 6: The Feed Intake Monitor by MBRose, with a) group-housed or b) individually-housed
configurations. (Source: www.mbrose.dk)
5. Welfare and Human/animal interaction
The laboratory pig is in a position to receive far greater human contact than its commercial farm
counterpart. A recent estimate for Dutch commercial pig production is that the caretaker has so
many animals under their care that they can only spend about 1 second a day on each individual pig
during the course of their daily duties (H Hogeveen, personal communication). In a laboratory pig
environment, there is clearly much more opportunity for the caretaker to spend time with individual
pigs and forge a positive human-pig relationship . Indeed, depending on the purpose for which the
pig is being kept, it may be essential that the caretaker spend many hours with each individual, not
only for daily care and maintenance, but also training for specific procedures, such as dosing, blood
draws, behavioral training, etc.
a. General concepts – positive/negative/minimal, individual recognition
The quality of human-animal interaction has significant impact on the animal’s welfare (Tallet et al,
Chapter 11, this volume). There is a large amount of research evidence to show that pigs subjected to
negative handling show increased fear of humans and that this is reflected in the pigs behavior,
a)
b)
physiology and production performance (see review by Spoolder and Waiblinger, 2009). Negatively
handled pigs grow slower, have poorer reproductive performance, are more reluctant to approach
humans and have increased plasma cortisol concentrations. In a laboratory setting, such responses
would greatly impact the quality of the data being collected.
The amount of human-pig interaction needed to induce these effects is very small. For example, 30
seconds of negative handling a day can result in strong behavioral aversion towards humans
(Hemsworth and Barnett, 1991). Also, being a pig within a group subject to negative handling is
sufficient to induce the response in all individuals within the group (Hemsworth and Barnett, 1991).
However, the converse is also the case – small amounts of positive handling can result in a reduction
in fearfulness (Hemsworth et al., 1987), though inconsistency can be as adverse as negative handling
alone (Hemsworth et al., 1987).
Many pigs used for laboratory studies may undergo repeated procedures that are painful or aversive,
and thus, it could be argued that they will encounter inconsistency, in terms of the pig’s perception
of whether the interaction with the human is positive or negative. It may then be useful to know if
the pig can compartmentalize the negative experiences and associate them with specific people or
situations, leaving its more general interactions with its caretakers uninfluenced by the negative
events. On farm, Hemsworth et al. (1994) found that pigs handled using either predominantly
positive or negative interactions showed stimulus generalization and were unable to distinguish
between the handlers. However, where the amount of handling increased above that likely on
commercial units, they did find that pigs could discriminate and would choose to interact more with
a familiar handler over an unfamiliar handler (Hemsworth et al. 1996). Other studies have shown that
pigs cannot only discriminate between individuals based on clothing color (Koba and Tanida, 1999)
but also use olfactory and visual cues (Koba and Tanida, 2001). Brajon et al. (2015a,b) have
demonstrated that positive and negative handling can be remembered by the pig and will influence
subsequent behavior towards humans. However, importantly, experience of negative handling does
not result in lasting aversion of humans: for example, pigs experiencing negative handling from
handler B after a period of positive handling carried out by handler A, maintain a high motivation to
explore and spend time with handler A (Brajon et al. 2015a). There may still be generalization though,
and the direction of this may be dependent on the behavior of the handler. Those pigs which
experienced both positive and negative handling generalized their positive experience when the
handler was motionless (i.e. passive) but generalized their negative experience when the handler
approached them (i.e. active).
Taken together, these results indicate that pigs can certainly discriminate between individual
handlers and that negative interactions with one handler need not damage the relationship with
other handlers. Aversive procedures can perhaps be assigned to a person other than the regular
care-taker but it might also be that the presence of the regular care-taker during an aversive
procedure may act as social support and reduce the pig’s response to the procedure – i.e. that a
strong positive human-pig relationship can improve the welfare of the pig. We do know that
oxytocin is implicated in social bonding and we know that positive human contact results in a
sustained increase in oxytocin measured in the cerebral spinal fluid of pigs (Rault, 2016). In other
species, positive interactions with a human are sought by the animal (Bertenshaw and Rowlinson,
2008) and appear to elicit indicators of pleasure (Schulze Westerath et al., 2014). Thus, the possibility
exists for a predictable, positive human-animal relationship to tangibly enhance the animal’s welfare
and perhaps provide a form of environmental enrichment (Claxton, 2011). This area could benefit
from further study.
b. Training for procedures – weighing/blood sampling/dosing, etc.
Anyone who has worked with pigs is quickly aware that they are intelligent. The scientific literature
shows that pigs are capable of learning and remembering complex tasks and anecdotal evidence of
the pig’s ability to assimilate information and use it to its own advantage is widespread, especially in
the acquisition of food. Quantification of an animal’s intelligence relative to other species is never
simple, but judgment places the pig at the upper end of the scale, either just below companion
animals like the dog and cat (Davis and Cheeke, 1998) in the case of a survey of university faculty and
students or, following a review of the literature, with similar “complex ethological traits” to dogs
and chimpanzees (Marion and Colvin, 2015). This intelligence not only confirms that their
environments should contain complexity (see above), but also means that they can be trained in
order to make procedures within the laboratory setting less stressful for the pig and less stressful for
the handler or carer. This intelligence and trainability applies equally to both the farm pig and the
laboratory breeds (Murphy et al., 2013).
Within a laboratory setting, there may be several procedures that will become routine such as
weighing, and restraint for dosing, either orally or via IM, IV or SC routes, and for blood sampling.
Much of the aversive elements of these procedures can be reduced by subjecting the pig to operant
conditioning using rewards and/or punishments. The most often-used and recommended technique
is that of positive reinforcement, whereby the pig is given a reward, usually a food reward, when the
desired behavior is carried out (e.g. Sørensen, 2010 – see Table 3).
Table 3: Representation of the four quadrants depicting options for methods of operant
conditioning
Reinforcement
Punishment
Positive
(Stimulus added)
Positive Reinforcement
Pleasant stimulus added to
desired behavior
Positive Punishment
Aversive stimulus added to
undesired behavior
Negative
(Simulus removed)
Negative Reinforcement
Aversive stimulus removed to
desired behavior
Negative Punishment
Pleasant stimulus removed to
undesired behavior
The reward can be paired with a conditioned reinforcer, such as a clicker, to aid communication
between pig and handler and act as a simple, unemotional cue (Arblaster, 2010). For a detailed
description of training methods to help handling, dosing and sampling of laboratory pigs, an
excellent resource is the Ellegaard Göttingen Minipigs educational package (Zeltner, 2013), which
gives detailed coverage of training methods in relation to various common procedures. With
sufficient time and consistency of interaction, pigs can be trained to be at ease during certain
procedures (see Figure 7).
Figure 7: Pig sitting and having blood sampled via multiple splanchnic vascular access ports. (Source:
Helle Nygaard Lærke, Aarhus University)
In reality, positive reinforcement is often paired with negative punishment, in that an unwanted
behavior results in the removal of a pleasant stimulus. In this way, desired behavior is rewarded and
increased, while undesired behavior is unrewarded and decreased, with the relationship between
the animal and the handler largely maintained as positive. Use of negative reinforcement and
positive punishment involves the handler applying aversive stimuli. Even though such techniques
may result in the looked-for changes in behavior, associating the handler with negative experiences
can induce fear and distress. There is little scientific literature on the relative effectiveness of the
different training methods with pigs, but work on other species - primarily dogs – indicates that
positive punishment in particular can result in anxiety and increased probability of problem behaviors
(Hiby et al., 2004). However, Zeltner (2013) describes two situations in which positive
punishment/negative reinforcement can be used to train minipigs to tolerate handling and being in a
sling.
6. Management and alleviation of pain and discomfort
Even though the welfare of the large breeds of pigs kept as meat-producing animals has been
subject of study for decades, the pig is among the least examined of the mammalian species held by
man in terms of knowledge about pain (as reviewed by Herskin and Di Giminiani in chapter 3, this
volume). Considering that a large proportion of experimental pig studies involve tissue damage and
potentially pain, this is a major challenge for the documentation of the animal welfare standard,
which is needed in order to comply with the legal, ethical and scientific responsibilities of in vivo
animal research.
As reviewed by Viñuela-Fernández et al. (2007), unmitigated pain is a major animal welfare concern,
and unacceptable from a 3R perspective. Recently, Bradbury et al. (2015) reviewed biomedical
literature and found that only remarkably few of the model studies involving porcine surgery
reported whether and how the pain level of the animals were assessed. As no “golden standard” for
the presence of pain exists (Rutherford, 2002), what can be quantified and reported is indicators –
measurements which give indication of the nature and severity of the pain experienced. The current
knowledge about porcine indicators of pain have been reviewed by Herskin and Di Giminiani in
chapter 3 of this volume. Below, we discuss examples considered especially relevant for pigs used
for research purposes.
For the large proportion of laboratory pigs which undergo surgery or other types of tissue damage,
the procedures (or the concurrent anaesthesia) may influence traditional physiological pain
indicators. Hence, Flecknell (1994) recommended that documentation of pain states in laboratory
animals focus on behavioural indicators, especially in cases involving post-surgical pain.
Across studies, feasibility of pain management benefits from assessment techniques characterized
by high through-put. One such option, which can be done relatively quickly in pigs, might be the use
of evoked behavioural responses, such as the quantification of avoidance responses to a
standardized mechanical challenge (as for example described by Di Giminiani et al., 2013).
Comparable methodology have been used in piglets (Fosse et al., 2011) or sows (Pairis-Garcia et al.,
2015b) after experimentally induced inflammatory states mimicking conditions known from
commercial pig production, as well as in studies modelling human pain (Castel et al., 2014; 2016).
Swindle and Sistino (2015) described how responses to palpation as part of a clinical examination can
be graded and used as part of the assessment of painful conditions in laboratory pigs. However,
recently the clinical relevance of evoked behavioural responses has been debated in rodents (e.g.,
Mogil, 2009), including a call for more ecologically relevant measures, for instance obtained by
manipulation of the motivational states of the animals (e.g., Andrews et al., 2012). In pigs, Fosse et al.
(2011) examined the motivation of piglets to pass a wooden ramp in order to get access to
mother/siblings as a measure of the consequences of experimentally induced lameness.
In contrast to evoked behavioural responses (be it after standardized challenge or motivational
tasks), quantification of the non-evoked animal behavior is highly time consuming, but may provide
important information about potential ongoing pain, which is critical as part of the required
monitoring of laboratory animal welfare and may otherwise be missed. However, spontaneously-
occurring behaviour has received almost no attention in porcine model studies relevant for pain. One
suggested non-evoked behavioural indicator of pain in laboratory pigs is the latency to onset of
feeding after surgery or another experimental procedure (Andersen et al., 1998; Malavesi et al.,
2006). Future studies, preferably taking advantage of the knowledge from pigs kept for meat
production, should focus on the validation of behavioural indicators of pain in pigs used for research
in order to incorporate these measures into a welfare monitoring tool.
Despite the distinct lack of validated methodology to monitor and document pain in laboratory pigs,
as well as lack of reporting of pain management (Bradbury et al., 2015), there are studies presenting
effects of analgesic drugs, and their use is also recommended in textbooks on laboratory pigs
(Swindle, 2015; Duedal Rölfing and Swindle 2015). Among examples of the studies are Pairis-Garcia et
al. (2015a,b), documenting effects of an NSAID administered to sows in a transient lameness model.
Reyes et al. (2002) examined post-operative pain relief in mini pigs following implantation of a
central artery catheter via a inguinal incision, and used a multifactorial numerical rating scale inspired
by rodent scales to show that the use of NSAIDs was able to normalize the pain scores. There are,
however, also reports questioning the use of NSAIDs due to the possible insufficient analgesia when
provided to animals in moderate to severe pain (Fish et al., 2008) as well as unwanted side-effects
which may alter research outcomes. In reference to such possible contraindication of NSAIDs in
animal research, Royal et al. (2013) reviewed different alternatives for the alleviation of porcine pain
relief. As part of a refinement study, the use of ultra-sound guided regional anesthesia in pigs in a
femoral fracture model was tested and recommended.
Based on the current knowledge, pain monitoring of laboratory pigs should be done regularly,
especially in the hours after surgery or other tissue damage. At present, no validated pain scales exit
for pigs. Royal et al. (2013) presented a postoperative pain assessment method consisting of
frequent observation of non-evoked behaviour (such as latency to eat and activity level),
physiological indicators such as heart rate, combined with observations of evoked responses to
palpation as well as actions by the caretaker to stimulate physical activity. Murison et al. (2009)
reported another pain assessment procedure in laboratory pigs, which also included locomotion
scoring and interaction with handlers. These authors specified that especially persistent sitting and
reluctance to lie down were suggested as potential indicators of pain. Hence, even though no
porcine pain scales have been formally validated, several suggested scales exist, including measures
of evoked behavioural responses, non-evoked behavior, clinical measures and to some extent
physiological measures, and these may form the basis for future validation and adjustment of pain
scales covering tissue damaging procedures common in studies involving pigs.
Beside pain, there are other negative affective states that may be experienced by pigs kept for
research purposes. In this last part of the chapter, we will discuss two examples – consequences of
the pre-surgical fasting and of the restraint needed to obtain tissue samples from laboratory pigs.
According to Swindle & Smith (2015) presurgical fasting of 8-12h will empty the stomach and small
intestine, whereas colonic emptying usually requires fasting for 48-72h. During this period the
welfare of the pigs is not only challenged by hunger (Lawrence and Illius, 1989; see also D’Eath et al,
this volume) but also by the lack of chewable objects, as pigs will attempt to eat any environmental
enrichment (Swindle et al., 1994). In pigs kept for meat production, several studies have examined
the welfare consequences of the fasting required before slaughter (e.g., Dalla Costa et al., 2016).
However, effects of the required fasting on the welfare of laboratory pigs have not been examined
systematically and warrants further study in order to refine the procedures as much as possible and
to be able to offer substitute environmental enrichment, which may limit the effects of the
withdrawal of food and eatable materials.
Interestingly, Swindle and Smith (2015) mention that agricultural methods of restraining pigs (e.g. by
nose snare, which has been shown to lead to marked and sustained avoidance and stress responses
(Janssens et al., 1995)) are inappropriate for laboratory pigs and provide examples of other
restraining devices such as slings, the use of which are less severe for the welfare of the animals. In
her paper “Never wrestle with a pig….”, Sørensen (2010) discussed how positive reinforcement
training may be efficient in order to facilitate sampling of tissue from laboratory pigs and may
improve animal welfare as well as the quality of research, thus emphasizing the potential advantages
from training and habituation of laboratory pigs before exposing them to experimental procedures.
7. Future trends and Conclusions
Although numbers are difficult to quantify, it is likely that the popularity of the pig as a laboratory
animal will continue to increase, and the potential applications of the pig will expand. At present,
there is a paucity of scientific literature available on the laboratory pig with respect to welfare,
though the rate of citations of those publications has increased greatly over the last few years
(Figure 8). This demonstrates a need for information that is not currently being met by papers
specifically on laboratory pigs.
Figure 8: Number of publications and citations of studies that include search terms “welfare” and
“laboratory pig”, “laboratory swine”, “miniature pig”, “miniature swine” or “minipig” over the time
period 1985-2016 (Web of Science).
However, work done in order to improve/secure welfare of laboratory pigs should keep in mind the
existing knowledge about the pig as a meat producing animal including models involving tissue
damage but aimed at, for instance, age-detection in forensic cases (e.g. Barington and Jensen, 2016).
It is important to remember that a pig is a pig and that there is a great deal of useful information
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available on pigs as farm animals that can be directly applied to pigs as laboratory animals, be they
farm pigs being kept for laboratory purposes or smaller purposebred pigs for laboratory use.
As the uses for pigs as laboratory animals increase, new welfare challenges may arise for which there
is little current information. For example, the population of pigs kept for meat production may host
many candidates for spontaneous animal models yet to be determined (Duncan et al., 2015) such as
canine osteoarthritis models (Lascelles et al., 2009), and for which the welfare implications are
unknown. The presence of such possibilities may also raise ethical debate in terms of whether it is
more ethically acceptable to “use” farm animal species for such experimentation rather than
companion animal species, or less acceptable relative to rodents (e.g. Webster et al., 2010).
However, this will also need to be balanced against the fact that the spontaneous models may be
more biologically relevant compared to induced models and that the use of naturally spontaneous
models better serves the 3 Rs (Russell and Burch, 1959).
Another major area which may see expansion of pigs kept for laboratory purposes is drug
development for human medication. More and more suggest that the pig may be part of the solution
to some of the current translational problems. In drug development, it is estimated that only 1 in
10,000 potential drug molecules or new chemical entities (NCEs) make it to market. The vast majority
of the drop-out is in the pre-clinical phase, which includes animal testing. However, even among
compounds reaching clinical testing, only 10-20% reach market, which means that the translation
from ‘successful’ animal studies to human application is poor. Reasons for failure in the process may
be multiple, but there does need to be greater scrutiny of the animal testing phase. The animal
model needs to be applicable and relevant and there needs to be greater emphasis on both internal
and external validity. The animal species used needs to be closely examined and the pig may well
prove to be a good candidate species (Swindle et al., 2012). If so – even more research is needed in
order to be able to monitor welfare and pain in these animals.
To conclude, It is important to keep in mind that “the laboratory pig” covers several areas of
research – from classical animal models for humans to porcine models for porcine conditions.
Notwithstanding the purpose for which it is kept, the pig is an intelligent, social animal which is
biologically programmed to perform a complex behavioural repertoire reminiscent of its ancestor,
the wild boar. In order to maximize animal welfare, anyone taking care of the laboratory pig has the
duty to acquaint themselves with the biology of the pig and best serve the needs of the pig within
the constraints of the experimental protocol under which it is being kept.
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