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The welfare implications of large litter size in the domestic pig I: Biologica factors



Increasing litter size has long been a goal of pig breeders and producers, and may have implications for pig (Sus scrofa domesticus) welfare. This paper reviews the scientific evidence on biological factors affecting sow and piglet welfare in relation to large litter size. It is concluded that, in a number of ways, large litter size is a risk factor for decreased animal welfare in pig production. Increased litter size is associated with increased piglet mortality, which is likely to be associated with significant negative animal welfare impacts. In surviving piglets, many of the causes of mortality can also occur in non-lethal forms that cause suffering. Intense teat competition may increase the likelihood that some piglets do not gain adequate access to milk, causing starvation in the short term and possibly long-term detriments to health. Also, increased litter size leads to more piglets with low birth weight which is associated with a variety of negative long-term effects. Finally, increased production pressure placed on sows bearing large litters may produce health and welfare concerns for the sow. However, possible biological approaches to mitigating health and welfare issues associated with large litters are being implemented. An important mitigation strategy is genetic selection encompassing traits that promote piglet survival, vitality and growth. Sow nutrition and the minimisation of stress during gestation could also contribute to improving outcomes in terms of piglet welfare. Awareness of the possible negative welfare consequences of large litter size in pigs should lead to further active measures being taken to mitigate the mentioned effects.
© 2013 Universities Federation for Animal Welfare
The Old School, Brewhouse Hill, Wheathampstead,
Hertfordshire AL4 8AN, UK
Animal Welfare 2013, 22: 199-218
ISSN 0962-7286
doi: 10.7120/09627286.22.2.199
The welfare implications of large litter size in the domestic pig I: biological
KMD Rutherford*, EM Baxter, RB D’Eath, SP Turner, G Arnott, R Roehe, B Ask§,
P Sandøe, VA Moustsen§, F Thorup§, SA Edwards#, P Berg¶¥ and AB Lawrence
Animal Behaviour and Welfare, Animal and Veterinary Science Research Group, SRUC, West Mains Rd, Edinburgh EH9 3JG, UK
Department of Large Animal Sciences & Institute of Food and Resource Economics, University of Copenhagen, Groennegaardsvej 8,
DK-1870 Frederiksberg, Denmark
§Danish Agriculture and Food Council, Pig Research Centre, Axelborg, Axeltorv 3, DK-1609 Kbh V, Denmark
#School of Agriculture, Food and Rural Development, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, UK
NordGen, Nordic Genetic Resource Center, Norway
¥Department of Genetics and Biotechnology, University of Aarhus, DK-8830 Tjele, Denmark
* Contact for correspondence and requests for reprints:
Increasing litter size has long been a goal of pig breeders and producers, and may have implications for pig (Sus scrofa domesticus)
welfare. This paper reviews the scientific evidence on biological factors affecting sow and piglet welfare in relation to large litter size.
It is concluded that, in a number of ways, large litter size is a risk factor for decreased animal welfare in pig production. Increased
litter size is associated with increased piglet mortality, which is likely to be associated with significant negative animal welfare impacts.
In surviving piglets, many of the causes of mortality can also occur in non-lethal forms that cause suffering. Intense teat competition
may increase the likelihood that some piglets do not gain adequate access to milk, causing starvation in the short term and possibly
long-term detriments to health. Also, increased litter size leads to more piglets with low birth weight which is associated with a variety
of negative long-term effects. Finally, increased production pressure placed on sows bearing large litters may produce health and
welfare concerns for the sow. However, possible biological approaches to mitigating health and welfare issues associated with large
litters are being implemented. An important mitigation strategy is genetic selection encompassing traits that promote piglet survival,
vitality and growth. Sow nutrition and the minimisation of stress during gestation could also contribute to improving outcomes in terms
of piglet welfare. Awareness of the possible negative welfare consequences of large litter size in pigs should lead to further active
measures being taken to mitigate the mentioned effects.
Keywords:animal welfare, birth weight, litter size, mortality, piglet, sow
Following the initial domestication of the wild boar about
10,000 years ago (Larson et al 2011), humans began
selecting for particular traits in pigs (Sus scrofa domesticus)
creating a range of domestic breeds with different physical,
behavioural, physiological and reproductive characteristics.
In the last century, as knowledge about the principles of
inheritance increased, the process of selection in pigs has
been conducted in a more systematic fashion. Selection was
initially focused on physical appearance but, from the 1950s
onwards, production traits were increasingly used (Dekkers
et al 2011). Initially, major progress was seen in carcase
traits and growth rate while reproductive output showed
little gain. As a consequence, over most of the history of pig
production, litter size changed relatively little. However, as
pig production further increased in intensity, improvements
in litter size were achieved through better management and
nutrition and, more recently, through effective implementa-
tion of genetic selection for litter size.
The pig industry is subject to numerous drivers, but ulti-
mately its aim is to produce a quality product at a compet-
itive price and in a socially acceptable way (Webb 1998;
Spötter & Distl 2006). The drive for increased litter size
is a consequence of the desire to improve production effi-
ciency by increasing the number of slaughter animals
produced per sow. This maximises financial gains and
also reduces the environmental impact (per kg of product)
of pork production. However, concern has been expressed
that increasing litter size may be detrimental to animal
welfare (Prunier et al 2010).
This paper aims to provide an overview of the main welfare
concerns for piglets and sows resulting from biological
factors associated with large litter size. The welfare
concerns discussed include the association between large
Universities Federation for Animal Welfare Science in the Service of Animal Welfare
200 Rutherford et al
litter size and increased piglet mortality and morbidity,
behavioural implications of large litters, and long-term
outcomes of birth condition (including low birth weight;
[LBW]) and early life experience. Sow welfare impacts are
more uncertain, but are discussed in relation to the process
of carrying, delivering and raising a large litter. In addition,
the contributions of genetics and other sow factors to the
issue of litter size are discussed. A companion paper (Baxter
et al 2013; this issue) details how management factors asso-
ciated with handling large litter sizes affect pig welfare.
Litter size is defined in this paper as all piglets born alive
plus all piglets born dead (regardless of birth weight) that
appear normally developed and coloured. This excludes
fully or partly mummified piglets that did not survive to
term (type 1 stillbirths), but includes any normally
developed piglets, (classified as type 2 stillbirths: Alonso-
Spilsbury et al 2005) that may have died either just before
expulsion was initiated, during expulsion or just after being
expelled, as well as piglets that possess any malformation
that meant they were not viable. This definition is relevant
as any piglet so defined has participated in any intrauterine
crowding and in the birth process. The exclusion of type 1
stillbirth piglets is necessary, particularly when reporting
litter size data, as these animals are recorded in some
countries but not in others, making international compar-
isons of stillbirth prevalence difficult. However, it is
realised that mummified piglets may have participated in
intra-uterine crowding at earlier stages in development and
thus will be discussed in relevant sections where necessary.
Since the pig industry often focuses on viable piglets, our
definition may include more individuals than are recorded
under practical conditions. In addition, this definition may
differ from that used in other publications.
Welfare impacts on the piglet
For piglets, the biological consequences of large litter size
can be divided into outcomes that are causally related to a
crowded gestation environment and outcomes that are related
to experiencing post-natal life in a large litter. These two do
not perfectly co-vary since, either through early piglet
mortality or active management responses, such as cross
fostering, litter size during neonatal life will be less variable
than litter size during foetal life. Litter size at birth may not
reflect litter size in early pregnancy because of foetal loss.
Intra-uterine crowding
The first point at which litter size could be expected to
affect piglet biology is in the uterus. Pig species have a
natural propensity to conceive large numbers of offspring
and issues relating to foetal litter size have been reviewed
and discussed previously (Ashworth et al 2001; Foxcroft
et al 2006). Porcine ovulation rates are high, yet the uterine
space and/or uterine blood supply represents a limiting
resource. Of the released ova, 30–50% fail to survive
(Anderson 1978; Pope 1994; Geisert & Schmitt 2002) and
those that do survive must compete to acquire adequate
placental area for bloodflow and delivery of vital nutrients.
Embryos which implant later may be developmentally
disadvantaged due to hormonal secretions from more
developed embryos (Anderson 1978; Geisert et al 1991;
Pope 1994; Krackow 1997) and this might explain why
increased crowding in the uterine horns leads to the produc-
tion of extremely small piglets at birth (Perry & Rowell
1969; Dzuik 1985). Asynchronous development may be
part of the natural reproductive strategy of wild pigs; under
sub-optimal conditions piglet heterogeneity may mean that
larger siblings preferentially survive at the expense of
smaller piglets (Fraser 1990).
In most mammalian species it has been noted that a larger
litter size reduces average individual birth weight. This is
most obvious in species like humans, cows or the horse that
give birth to a small number of offspring, but has also been
described in polytocous species such as the pig. In non-
polytocous species the reduction of birth weight is partly
explained by a shorter gestation length, whilst polytocous
species will often go close to term even when carrying large
litters. In humans, the term ‘small for gestational age’
(SGA) has been used to indicate if the offspring is under-
weight even when compensating for reduced gestation
length. This correction is seldom relevant in polytocous
species. The consequences of reduced birth weight and
increased birth weight variation (as created by intra-uterine
conditions) for piglet welfare will be discussed later.
However, weight is not the only valid indicator of viability
and the consequences of the uterine environment. Measures
of body proportionality, such as the ponderal index, provide
a valuable indicator of mortality risk (Baxter et al 2008). As
a consequence, the distinction between a piglet being SGA
or having undergone intra-uterine growth retardation
(IUGR) is important. Although definitions vary, piglets
weighing less than the tenth percentile at birth, yet
displaying normal allometry, are often classified as SGA
whereas piglets that are disproportional (suggesting that
they have not reached their intra-uterine growth potential)
are classified as IUGR (Bauer et al 1998). The distinction
matters because SGA piglets may have more potential to
recover given proper management than IUGR piglets that
have other abnormalities meaning that they have low
viability. Some care does need to be taken when interpreting
findings in this area due to the differing methods and defi-
nitions used across different studies. Many of the identified
effects of LBW should be considered with an implicit
caveat that the effect may not be of LBW per se but could
relate to body proportionality or aspects of maturity.
Stillbirths, birth difficulties and asphyxia
Litter size is unfavourably associated (ie positively
correlated) with stillbirth prevalence (Svendsen et al
1991; Roehe & Kalm 2000; Van Dijk et al 2005; Canario
et al 2006a,b; Rosendo et al 2007; Kapell et al 2009) and
also with hypoxia and the production of low viability
piglets (Herpin et al 1996).
The extent of late foetal development and maturation plays
a major role in piglet survival (Randall 1972; van der Lende
et al 2001). In the last days preceding farrowing, the foetus
experiences an increase in growth rate (Biensen et al 1998)
and development, with final physiological preparations for
© 2013 Universities Federation for Animal Welfare
Welfare implications of large litters I 201
extra-uterine life. The risk of reduced gestation lengths
increases with increasing litter size (Leenhouwers et al
1999; Canario et al 2006b; Rydmer et al 2008;
Vanderhaeghe et al 2010a,b, 2011), possibly as a result of an
acceleration in the maturation of the foetal hypothalamic-
pituitary-adrenal (HPA) axis, resulting in higher foetal
cortisol levels reaching the uterus and the initiation of the
parturition process (Van Dijk et al 2005).
Prolonged farrowing duration and a large litter size increase
the risk of hypoxia (Herpin et al 1996). Hypoxia occurs
when the neonate experiences oxygen deprivation. This can
occur in utero as a result of poor oxygen supply via the
placenta or as a result of peri-natal asphyxia during parturi-
tion. Hypoxia can also occur post-natally if a piglet is born
inside the placenta or, in an immature piglet, if the lung
surfactant factor is not functional. Lung maturation is facil-
itated by production of lung surfactant, which is a heteroge-
neous mixture of lipids and proteins that spreads in the lung
tissue/air interface, preventing alveolar collapse during
expiration and allowing the alveoli to open easily during
inhalation (Winkler & Cheville 1985).
Meconium aspiration syndrome (MAS) may be more likely
to occur with large litter sizes, and is a risk factor for still-
birth or early post-natal death either by reduced vitality,
myocardial dysfunction or lung damage (Mota-Rojas et al
2002; Alonso-Spilsbury et al 2005). MAS occurs when the
foetal piglet experiences asphyxia and a surge in foetal
cortisol levels cause the sphincter muscle to relax and thus
a release of faecal matter (meconium) into the amniotic sac.
When the foetus experiences severe distress (eg a surge in
uterine pressure) it can aspirate this meconium and amniotic
fluid. Some piglets are born alive but swallow a lot of
amniotic fluid and/or meconium and then die; effectively
these piglets drown in their own placental fluids and are
often mistakenly classified as being stillborn.
Peri-natal mortality and morbidity
Overall, litter size has been found to be unfavourably associ-
ated with peri-natal mortality in many studies (van der Lende
& de Jager 1991; Blasco et al 1995; Johnson et al 1999;
Sorensen et al 2000; Lund et al 2002). However, recent work
(discussed later) has shown that despite this antagonistic
correlation, a positive genetic trend can be obtained in both
traits (in line with quantitative genetic theory) (Nielsen et al
2013). Mortality may also be high in very small litters
(Cecchinato et al 2008), often reflecting a pathology in
reproduction. The negative relationship between litter size
and birth weight is of critical importance to many aspects of
piglet welfare including risk of mortality (Gardner et al
1989; van der Lende & de Jager 1991; Kerr & Cameron
1995; Roehe 1999; Roehe & Kalm 2000; Sørensen et al
2000; Tuchscherer et al 2000; Knol et al 2002a,b; Quiniou
et al 2002; Wolf et al 2008; Fix et al 2010; Pedersen et al
2011a). As well as being associated with lower birth weight,
large litter size is associated, as a consequence of asynchro-
nous embryo development, with increased within-litter
weight variation (Roehe 1999; Milligan et al 2002; Quiniou
et al 2002; Quesnel et al 2008; Wolf et al 2008).
The main causes of neonatal piglet mortality are chilling,
starvation and crushing by the sow, and these three causes
interact (Edwards 2002; Andersen et al 2011). Large litter
size may be associated with increased risk of chilling (since
LBW piglets show poorer thermoregulatory abilities:
Hayashi et al 1987; Herpin et al 2002), starvation (since
small and/or chilled neonates are less vigorous when
competing at the udder) and crushing (since weakened
piglets may be less responsive to the movements of the
sow). For LBW piglets, the risk of crushing is increased
because they spend longer near the sow’s udder (Weary et al
1996). Thus, it is possible that a vulnerable neonate may
experience chilling, starvation and then crushing (Edwards
2002), which highlights the considerable welfare issues
surrounding piglet mortality. The majority of pre-weaning
mortality occurs in the first 72 h of life (Edwards 2002).
However, piglets are at additional long-term risk from
disease if they have failed to acquire sufficient immunity
from colostrum as a result of delayed or limited suckling in
the immediate post-natal period.
Large litter size was found to be a risk factor for piglet knee
abrasions (Norring et al 2006), which are both a direct
welfare problem and a risk factor for pathogen entry to the
body. LBW has also been found to have a negative impact
on bone development (Romano et al 2009). Moreover, large
litter size and LBW are associated with increased preva-
lence of splayleg (Sellier & Ollivier 1982; Vogt et al 1984;
Van Der Heyd et al 1989; Holl & Johnson 2005).
Teat competition and establishment of the ‘teat order’
Piglets find and take ownership of a particular teat, or pair
of teats, during the hours after birth (Scheel et al 1977;
Pedersen et al 2011b), and then consistently return to this
teat/pair at each suckling, displaying ‘teat fidelity’ (Gill &
Thomson 1956; Newberry & Wood Gush 1985; de Passillé
et al 1988). After approximately 12 h, milk is only let down
from the teats for a few seconds (8–10 s: Pedersen et al
2011b) once or twice an hour (Fraser 1980). Consequently,
there is competition to take possession of functional teats
and a stable ‘teat order’ emerges whereby piglets occupy the
same teats at each suckling bout (Fraser 1975; de Passillé &
Rushen 1989). The heaviest piglets are more likely to win in
fights for teats (Scheel et al 1977). In larger litters, since teat
number has not increased in step with litter size, there is
inevitably greater competition for teats (Milligan et al 2001;
Andersen et al 2011). Piglets which cannot access a func-
tional teat face a critical situation and typically starve to
death in the first one to three days (English & Smith 1975;
Hartsock & Graves 1976; Fraser et al 1995). Occasionally,
more than one piglet will share one teat and this usually also
causes problems for at least one of the sharing pair (de
Passillé et al 1988) as the competition to defend a teat can
be aggressive. Many of the effects of larger litter size
discussed in this paper are continuous (ie they change
gradually with increasing litter size), but in relation to teat
competition, there is clearly a threshold effect: once a litter
has more viable piglets than functional teats, fostering or
some other management intervention is needed, and once a
Animal Welfare 2013, 22: 199-218
doi: 10.7120/09627286.22.2.199
202 Rutherford et al
batch of sows farrowing at the same time have more piglets
than teats, a new level of intervention, such as nurse sows or
artificial rearing methods, are needed. Baxter et al (2013)
discuss in more detail management issues relating to large
litters, such as cross-fostering and teeth resection.
Long-term effects of litter size and birth weight
A large experimental and epidemiological literature, across
many species, shows that birth weight relates to many
aspects of an individual’s biology throughout life.
Stress physiology
Birth weight has been shown to impact upon pigs’ stress
reactivity later in life. LBW neonatal piglets had larger
adrenal glands, increased circulating levels of cortisol,
higher cortisol binding capacity and a greater cortisol output
from adrenocortical cells compared to larger piglets
(Klemcke et al 1993). Similar effects have been observed
beyond the immediate neonatal period. Kranendonk et al
(2006) found that LBW piglets had a higher cortisol
response to challenge at day 41 of age compared to larger
birth weight piglets. Poore and Fowden (2003) found that
HPA reactivity was increased in LBW piglets at 3 months of
age, along with overall adrenal size and an increased ratio
of adrenal cortex to medulla in comparison to heavier
piglets. In another study (Poore et al 2002), blood pressure
at three months of age was found to be inversely associated
with birth weight and, more significantly, with a measure of
body disproportion. Heavier birth weight has also been
associated with a stronger rhythmicity of cortisol release at
nine weeks of age (Munsterhjelm et al 2010). Overall, these
findings suggest that LBW piglets have a permanent alter-
ation to the functioning of their HPA axis, implying an
increased stress reactivity throughout their lifetime.
However, without reference to other variables (such as
behavioural indications of altered emotionality, or negative
effects on immune function), the link between particular
states of HPA function and animal welfare is often not clear
(eg Mormède et al 2011), so only tentative conclusions
about the impact of such changes on welfare can be drawn.
Behavioural outcomes
Litter size could impact on behavioural outcomes, with
relevance for welfare, in a number of ways. Severe protein
malnutrition may alter brain development and thus
behaviour (eg Morgane et al 1993). Given that some piglets
from large litters may starve to death without intervention,
there are likely to be others that undergo severe under-
nutrition in early life and this could have implications for
later behavioural strategies. However, this possibility has
not been addressed in piglets.
Aggressive experiences at the teat could affect future
aggressive behaviour, although the available experimental
data are equivocal. D’Eath and Lawrence (2004) found that
piglets from larger litters in which there was more competi-
tion, were more aggressive after weaning. This result was
not repeated in a larger study where pigs were mixed into
new social groups at around seven weeks post weaning
(Turner et al 2006). However, these two studies are not
directly comparable since D’Eath and Lawrence (2004)
kept piglets in their ‘natural’ birth litters and used a direct
measure of aggression whereas Turner et al (2006) studied
a commercial unit in which cross-fostering for large litter
size did occur and they used lesion number as a proxy
measure of aggression. Chaloupkova et al (2007) found
some evidence of a relationship between increasing litter
size and decreased likelihood of agonistic interactions,
following post-weaning mixing, ending with one pig
chasing and biting at another, and also with a decreased
number of wounds. This might indicate, as suggested by
D’Eath (2005), who observed the consequences of pre-
weaning mixing of piglets, that piglets from larger litters are
more socially skilled than those from smaller litters. A
similar behavioural profile (early aggression, but longer-
term social stability) is also seen in pigs with high social
breeding values (Rodenburg et al 2010).
Although litter size could impact upon emotionality, as
demonstrated in rodents (Janczak et al 2000; Dimitsantos
et al 2007), this possibility has not been explored in pigs.
LBW piglets have been found to show memory deficits in
a cognitive hole board test (Gieling et al 2011) and to have
a decreased willingness to play (Litten et al 2003). Play
represents a useful indicator of positive welfare and its
absence is often associated with situations of decreased
welfare (Held & Spinka 2011).
Health implications
The pig has been extensively studied as a model for the
health effects of LBW/IUGR in humans. Small piglets,
studied using either the natural variation in within-litter
birth weight in modern genotypes, or through artificially
induced growth retardation, show alterations in the trajecto-
ries of growth and development of major biological
systems. The accelerated maturation of some of these
systems may be seen as evidence of developmental adapta-
tion to a compromised uterine environment. For example,
rapid morphological development and enhanced contractile
ability of skeletal muscle and an increased cardiac output
have been described in LBW piglets (Bauer et al 2006).
However, many biological functions appear to be impaired
by LBW and thus large litter size, and its associated uterine
crowding and compromised placental efficiency, may be
expected to exacerbate these developmental abnormalities.
There is evidence of compromised growth of the gastroin-
testinal tract, liver, kidneys, thymus, ovaries, muscles and
skeleton in LBW piglets (Handel & Stickland 1987; Xu et al
1994; Bauer et al 2002; Da Silva-Buttkus et al 2003;
Mollard et al 2004; Wang et al 2005; Morise et al 2008;
Cromi et al 2009). The tissue-specific decrease in expres-
sion of proteins that regulate immune function, interme-
diary metabolism and tissue growth may explain the
abnormal growth and functioning of these systems (Wang
et al 2008). Studies of the human health impacts of LBW
have primarily focused on the incidence of chronic cardio-
vascular and metabolic diseases of adulthood. Of more
immediate relevance for pig production are observations in
humans of heightened risk for infectious diseases associated
© 2013 Universities Federation for Animal Welfare
Welfare implications of large litters I 203
with LBW (Moore et al 1999; McDade et al 2001; Amarilyo
et al 2011). Although these effects have been little studied
in pigs, there is evidence of increased adhesion of bacteria
to the poorly developed ileum and colon of piglets born
after IUGR (D’Inca et al 2011) and such piglets show a
reduced lymphocyte proliferation in response to a mitogen
challenge (Tuchscherer et al 2000). Renal functions are also
compromised by an LBW leading to a reduction in
glomerular filtration rate (Bauer et al 2002) which could
heighten the risk of urinary infection.
An important post-natal effect of the diffuse epitheliocho-
rial nature of the porcine placenta is that piglets are born
without immune protection, and have to acquire maternal
antibodies through the ingestion of colostrum (Gaskin &
Kelly 1995). The difficulty of acquiring colostrum, partic-
ularly in a large litter, has been described above. Some
have argued that the competence of the passive immune
response acquired in this way, in practice, differs little
between piglets (Fraser & Rushen 1992; Damm et al
2002). However, the sow’s colostrum yield appears to be
independent of litter size (Devillers et al 2007; Quesnel
2011). As a consequence, competition between large
numbers of littermates would, on average, be expected to
result in a smaller and more variable quantity of colostrum
intake per piglet (Le Dividich et al 2005), although it is
not clear whether this lesser quantity is still sufficient for
piglets. Colostrum intake below 200 g per piglet in the
first 24 h of life is a significant risk factor for piglet
mortality (Devillers et al 2011). Issues to do with piglet
colostrum intake have recently been thoroughly reviewed
by Quesnel and colleagues (2012).
In combination with physical and mental developmental
immaturity and the low vigour of small piglets from large
litters, teat competition may constitute a further risk factor
for disease. The pre-weaning mortality rate from infec-
tious disease is seen to be disproportionately high in LBW
piglets compared to heavier piglets (Tuchscherer et al
2000). There is some evidence in rats that litter size can
impact on later immune function. Prager et al (2010)
found evidence of negative correlations between litter size
and aspects of adaptive immunity, and positive correla-
tions with measures of innate immunity.
Welfare impacts of large litter size on the sow
Although numerous studies have addressed welfare issues in
gestating sows (eg Marchant-Forde 2009), these have not
focused on the specific fact that the animals concerned are
pregnant. Furthermore, they have not given any considera-
tion as to whether the foetal litter size being borne has any
impact on sow welfare. However, in late pregnancy, sows
face many challenges, including the energetic and nutrient
demands of growing foetuses, hormonal changes, general
discomfort and restriction of movement, and effects on sleep
and rest. Moreover, within commercial farming systems
there are additional challenges such as group dynamics,
access to resources and resting areas and issues related to
feed quantity and delivery. Increased metabolic loading on
sows during pregnancy could also increase the risk of heat
stress in countries where this is an issue. Though not inves-
tigated in pregnant farmed animals, there is evidence in mice
that litter size during pregnancy can affect behavioural char-
acteristics of the mother; both maternal aggressiveness and
anxiety increase with increasing litter size (D’Amato et al
2006), presumably an adaptive response reflecting the
greater reproductive value of the litter.
Although, from human experience, giving birth is reported
to be an extremely painful process (Melzack 1992), the pain
experienced by non-human animals during parturition has
received little scientific interest (although see Mainau &
Manteca 2011). Labour pain is initiated in the uterus due to
dilation of the cervix and contraction of the lower uterine
segment and there is a correlation between the degree of
dilation and the intensity of pain experienced by humans
(Bonica 1986). There is also a correlation between the onset
of uterine contractions and the onset of pain (Corli et al
1986). An endogenous opioid-mediated analgesic system
exists in parturient rats (Gintzler 1980), humans (Cogan &
Spinatto 1986) and in the pig (Jarvis et al 1997). Opioid-
mediated analgesia at parturition may act as a defence
against labour pain but increased release of opioids in
response to nociception may also interfere with parturition
and maternal behaviour by the inhibition of oxytocin
(Lawrence et al 1992). Thus, the prolonged farrowing
duration associated with large litter size could cause
increased release of opioids in response to nociception and
thus impact on maternal-offspring bonding.
As litter size increases, average piglet birth weight decreases
(Johnson et al 1999; Roehe 1999). This may reduce pain at
expulsion of each foetus but parturition may last longer and
the cumulative effects may be greater. It has been suggested
that longer farrowings and increased numbers of stillborn
piglets (both of which are associated with larger litters) are
risk factors for sows experiencing increased pain in the
parturient period (Mainau et al 2010; Mainau & Manteca
2011). Pain experienced by the sow during farrowing is of
obvious welfare concern in its own right, but may have
several additional consequences. It has been suggested that
pain may be involved in the aetiology of savaging (Mainau
& Manteca 2011) and could also have an impact on other
aspects of poor mothering, such as likelihood of crushing
(Haussmann et al 1999), as sow discomfort is associated
with increased postural changes (Mainau et al 2010).
Parturition is energetically demanding and increasing litter
size may increase those energy demands. In addition to
parturition pain, sows can experience uterine and maternal
fatigue, which can lead to dystocia (Lay et al 2002) or the
cessation of farrowing. Uterine fatigue or secondary uterine
inertia means the uterus ceases to perform meaningful
contractions and this can increase the risk of asphyxia and
stillbirth. Maternal exhaustion refers to the inability to suffi-
ciently increase intra-uterine pressure by contractions of the
abdominal muscles and diaphragm. Serious health compli-
Animal Welfare 2013, 22: 199-218
doi: 10.7120/09627286.22.2.199
204 Rutherford et al
cations may arise in the sow from exhaustion during labour
and such sows often require attention during parturition (to
pass the last piglets either manually and/or medically with
injections of a drug such as oxytocin to restart contractions)
or after parturition (eg to treat hypocalcaemia). However,
exogenous oxytocin has the potential to increase the risk of
stillbirth and may cause additional stress for the sow (Mota-
Rojas et al 2002, 2005, 2006).
Lactation and post weaning
During the immediate post-parturient phase, before any
management interventions such as fostering might relieve
the pressure of a large litter, the sow will be required to
nurse her newborns. As cyclical let down starts, competition
for teats becomes apparent. Disputes at the udder will
influence maternal behaviour (by causing discomfort:
Fraser 1975), but could also influence maternal health.
Damage to the udder, caused by piglets’ needle teeth, may
be painful to the sow and could lead to infection.
As lactation progresses, and the energy demands become
more intense, sows will further mobilise their body reserves
(Quesnel & Prunier 1995). During lactation, the sow often
enters a catabolic state, facilitating the mobilisation of body
fat into milk (Uvnäs-Moberg 1989). Demands for milk
synthesis increase with litter size and, if sows cannot
maintain a high feed and water intake, they will start to lose
body condition and may be at greater risk of developing
injuries such as shoulder sores. Shoulder sores may develop
during the first and second week of lactation in sows that are
too lean at farrowing and are presumed to be painful
(Zurbrigg 2006; Herskin et al 2011). In an epidemiological
study on Danish farms, weaning weight of the litter was
shown to be positively associated with the prevalence of
shoulder sores (Bonde 2008). This could be as a consequence
of better nursing by the sow, and therefore more lateral
recumbency, or a result of the energetic demands of raising a
larger litter and its subsequent effect on body condition score.
Biological mitigation approaches
Genetic contributions to litter size issues
Approximately two decades ago, the introduction of the best
linear unbiased prediction (BLUP), including large-scale
pedigree information, facilitated selection for traits of lower
heritability, making substantial genetic improvement in
litter size possible in dam lines. A simulation study (Roehe
1991) and a selection experiment (Sørensen et al 2000)
indicated that a selection response (increase) of about 0.4
piglets per generation could be achieved. Subsequently,
several pig-breeding companies have reported that selection
has resulted in increased litter sizes. For example, in
Denmark, selection for litter size (total born piglets) was
initiated in 1992 and from 1996, the litter size (total born
piglets per litter) increased by 0.3 piglets per year, on
average (Table 1, which also shows UK figures for compar-
ison). The National Pig Breeding Program of Australia
reported an increase of 0.5 piglets from 1999 to 2004
(Taylor et al 2005), and a Serbian selection experiment
reported an increase of ~0.25 piglets per year on average
from 2001 to 2011 (Vidović et al 2012). The Dutch TOPIGS
company increased litter size by ~0.16 piglets per year on
average from 2001 to 2009 (Merks et al 2010), as did the
Pacific Ocean Breeding Co Ltd in Japan from 2003 to 2008
(Tomiyama et al 2011).
Whilst genetic selection methods have played an important
role in increasing litter size in pigs, research also suggests that
piglet survival can be improved genetically either through
direct selection for survival or by selection for related traits.
There are several alternative genetic strategies that may
therefore play a role in mitigating some of the negative
welfare outcomes of litter size and these are discussed briefly
here, and in more detail by Rutherford et al (2011).
Selection for piglet survival
Piglet survival is affected by two genetic components,
firstly direct genetic effects on the potential of the piglet for
survival, and secondly maternal genetic effects on the
mother’s potential to provide optimal conditions for piglet
survival. The direct effect of piglet survival tends to be less
heritable than the maternal effect under indoor conditions
(Lund et al 2002; Arango et al 2006; Su et al 2008; Kapell
et al 2011). Moreover, there are negative genetic correla-
tions between direct genetic and maternal genetic effects
(Arango et al 2006; Su et al 2008; Roehe et al 2010; Kapell
et al 2011). Selection for overall survival in the pre-weaning
period has the advantage that the trait is easy to record and
has a relatively high prevalence. Heritabilities of overall
survival are low (Grandinson et al 2002; Arango et al 2006;
Strange 2011) and those for specific individual causes such
as stillbirth or crushing, tend to be even lower (Grandinson
et al 2002; Hellbrügge et al 2008; Strange 2011), suggesting
that selection for overall mortality will yield a higher
genetic response than selection for underlying mortality
traits. Higher heritabilities of piglet survival traits have been
found under outdoor conditions (Roehe et al 2010),
suggesting that the more challenging environment of
outdoor farrowing increases the amount of information
available for genetic evaluation.
Selection against peri-natal mortality (up to day 5) yields
slightly higher heritabilities (Grandinson et al 2002; Su et al
2008) than later pre-weaning mortality (Su et al 2008).
Genetic correlations between peri-natal and later survival are
reported to be low indicating that peri-natal and post-natal
piglet survival are under different genetic control (Arango
et al 2006; Su et al 2008; Roehe et al 2009, 2010), and
should be treated as different traits. This supports research
examining phenotypic traits of piglet survival under outdoor
conditions (Baxter et al 2009, 2011): peri-natal survival was
explained by piglet shape and size, whereas post-natal
survival relied heavily on piglet and maternal behaviour.
Similarly, in a recent Danish study, stillborn mortality was
found not to be genetically correlated with mortality after
birth until weaning (Strange 2011).
Selection on an indicator of survival was implemented in the
Danish breeding programme in 2004, where the selection
criterion was changed from litter size (total number born) to
LP5 (number of live piglets at day 5). Since then, survival
© 2013 Universities Federation for Animal Welfare
Welfare implications of large litters I 205
rate until day 5 has increased by 6 percentage points in these
breeding herds, resulting in ≥ 20% less mortality (Nielsen
et al 2013). Total number born and LP5 in Yorkshire sows
increased by 0.3 and 1.4 piglets per litter and 1.3 and 2.1
piglets per litter in Landrace (Nielsen et al 2013). This
response should become apparent at the production level as
dissemination of genes from the purebreds to the crossbred
sows increases over the coming years. LP5 has a high,
positive genetic correlation with number of weaned pigs as
well as moderate, positive genetic correlations with survival
rate at birth and survival rate until five days (Su et al 2007)
and should, therefore, include the majority of piglet
mortality until weaning (Edwards 2002). Also, the Dutch
TOPIGS company has shown that piglet mortality can be
reduced simultaneously with increasing litter size, as they
have obtained a reduction in mortality of ~1 percentage point
from 2006 to 2009 simultaneously with increasing litter size
by 0.4 piglets (Merks et al 2010).
Animal Welfare 2013, 22: 199-218
doi: 10.7120/09627286.22.2.199
Table 1 National litter size and piglet mortality statistics in Denmark and the UK between 1996 and 2011.
Data taken from British Pig Executive (BPEX) Pig yearbooks 1996–2012 (British Pig Executive, Kenilworth, UK) and from Danish Pig
Research Centre (PRC) annual reports 1999–2012 (PRC, Copenhagen, Denmark).
Stillborn figures do not include mummified piglets.
Pre-natal mortality is % of total born that are stillborn.
§Pre-weaning mortality includes pre-natal mortality.
1996 1997 1998 1999 2000 2001 2002 2003
Live born 11.2 11.3 11.5 11.7 11.9 12.1 12.3 12.6
Stillborn0.9 1.0 1.0 1.1 1.1 1.2 1.3 1.4
Weaned 9.9 10.0 10.2 10.3 10.4 10.5 10.7 10.9
Total born 12.1 12.3 12.5 12.8 13.0 13.3 13.6 14.0
Pre-natal mortality (%)7.4 8.1 8.0 8.6 8.5 9.0 9.6 10.0
Pre-weaning mortality (%)§18.2 18.7 18.4 19.5 20.0 21.1 21.3 22.1
Live born 10.8 10.9 11.0 11.0 11.0 10.8 10.9 10.7
Stillborn0.8 0.8 0.9 0.9 0.9 0.9 0.9 0.9
Weaned 9.6 9.7 9.8 9.8 9.9 9.6 9.7 9.6
Total born 11.7 11.7 11.9 11.9 11.9 11.8 11.8 11.6
Pre-natal mortality (%)7.1 7.2 7.2 7.5 7.7 8.0 7.5 7.4
Pre-weaning mortality (%)§17.9 17.1 17.6 17.6 16.8 18.6 17.8 17.2
2004 2005 2006 2007 2008 2009 2010 2011
Live born 12.9 13.2 13.5 13.6 14.0 14.2 14.5 14.8
Stillborn1.5 1.7 1.7 1.7 1.8 1.9 1.8 1.8
Weaned 11.1 11.3 11.6 11.7 12.1 12.2 12.4 12.7
Total born 14.4 14.9 15.2 15.3 15.8 16.1 16.3 16.6
Pre-natal mortality (%)10.4 11.4 11.2 11.1 11.4 11.8 11.0 10.8
Pre-weaning mortality (%)§22.9 24.2 23.7 23.5 23.4 24.2 23.9 23.5
Live born 10.7 10.9 10.8 11.1 11.2 11.2 11.2 11.4
Stillborn0.8 0.7 0.6 0.6 0.6 0.6 0.6 0.7
Weaned 9.6 9.7 9.4 9.7 9.8 9.8 9.8 10.0
Total born 11.5 11.6 11.4 11.7 11.9 11.9 11.8 12.0
Pre-natal mortality (%)6.9 6.1 5.3 5.1 5.3 5.3 5.3 5.4
Pre-weaning mortality (%)§16.5 16.4 17.5 17.1 17.6 17.6 16.9 16.7
206 Rutherford et al
Indirect selection for survival through birth weight traits
As noted earlier, phenotypically, individual birth weight is
closely associated with piglet survival. However, geneti-
cally, the relationship between individual birth weight and
survival seems to be complex. For example, Knol et al
(2002b) found no, or even unfavourable, genetic relation-
ships between birth weight and survival, whilst Grandinson
(2003) found a favourable correlation between crushing and
birth weight. Whilst it might be presumed that LBW piglets
are at the greatest risk from hypoxia and stillbirth, this is not
necessarily the case. At the phenotypic level, there is a
curvilinear relationship between birth weight and stillbirth
(Roehe & Kalm 2000) and very large piglets can be equally
at risk from hypoxia, most likely as a result of birthing diffi-
culties. Whilst birth weight is positively genetically corre-
lated to proportion of stillborn piglets (Grandison et al
2002; Damgaard et al 2003), these estimates may be biased,
because the genetic analysis assumes that there is a linear
association between traits. Researchers have therefore
concluded that breeding for increased birth weight will not
necessarily result in higher overall survival rate
(Grandinson et al 2002; Knol et al 2002b; Su et al 2008).
Alternatively, selection for an optimum birth weight may be
advantageous, considering that there is a non-linear associa-
tion between stillbirth and birth weight. Given the association
of high neonatal weight variation with lower survival and
more variable weaning weights (Roehe 1999; Milligan et al
2002; Quiniou et al 2002), there is an impetus to select for
more homogeneous litters (Damgaard et al 2003). Increased
litter size increases the heterogeneity or within-litter birth
weight variation (Roehe 1999; Milligan et al 2002; Quiniou
et al 2002) and increases the risk of mortality (Roehe & Kalm
2000). Reducing the heterogeneity of litters could potentially
be more important than the increase of individual birth
weight and this is not a new observation (English & Smith
1975), yet it has not been effectively addressed.
Selection for survival through sow mothering ability
Another possible strategy would be to breed for the sow’s
ability to nurse her piglets. Good mothering ability shows
genetic potential (Baxter et al 2011). Selection for sow
nursing ability could, for example, be done through
selection for more teats (Pumfrey et al 1980; Hirooka et al
2001). However, selection for greater teat number has
practical difficulties and may have undesirable side-effects,
ie if it is associated with a longer spine and associated
defects. It has also been suggested that genetic and pheno-
typic correlations between teat number and other genetic
traits are undesirable (Pumfrey et al 1980). Another option
would be to select for a more general ability of the sow to
nurse her piglets, integrating underlying traits such as milk
yield and composition, teat number and sow maternal
behaviour (Knol et al 2002a).
Selection for survival through general robustness
Selection for a generally more robust neonate (Knap 2005)
may allow for increased litter size with fewer complica-
tions. Such a strategy may also deal with some of the issues
beyond mortality in which litter size has a contributory role.
Given the possible negative impacts on stress responsive-
ness and increased disease risk, breeding for improvements
in these traits has been explored in experimental studies
with pigs. However, there is high uncertainty as to what is
the best trait to breed for (eg Knap & Bishop 2000;
Morméde et al 2011) and care has to be taken that such
changes do not have unintended side-effects (D’Eath et al
2010). The concept of breeding for robustness has been
suggested in a number of livestock species (eg Star et al
2008). Knap (2005) has defined robust animals as animals:
that combine high production potential with resilience
to external stressors, allowing for unproblematic expres-
sion of high production potential in a wide variety of
environmental conditions.
Although it is not immediately clear how to breed for general
robustness, one possibility is through phenotypic plasticity or
the environmental sensitivity of the expression of genetic
production potential (De Jong & Bijma 2002; Knap 2005).
In terms of the biological characteristics of robustness,
lessons could perhaps be learnt from the biological profile
of the Meishan breed, which achieves a high level of prolifi-
cacy (Haley et al 1995; Farmer & Robert 2003), yet has a
lower risk of stillbirth (Canario et al 2006a), and better post-
natal piglet survival (Lee & Haley 1995), compared to many
Western breeds. Early studies comparing Meishans to non-
hyperprolific breeds found that they were able to support a
greater litter size (of smaller, uniform, piglets) to term (Lee
& Haley 1995; Ashworth et al 1997; Finch et al 2002). The
biology underlying this is complex, but a few key differ-
ences have been identified. Over the course of gestation, the
Meishan sow provides a more uniform supply of nutrients.
Foetal Meishan piglets show a slower growth rate (Wilson
et al 1998) putatively limiting intra-uterine growth retarda-
tion and maintaining litter uniformity. Meishan pigs show
homogeneity in early embryo size and this could be one
reason why they have greater litter sizes and lower embryo
loss (Bazer et al 2001). In Meishans, the increased demands
of foetuses in late pregnancy are met by a more efficient
rather than larger placenta. Meishans show increased
placental vascularisation in the final third of gestation
(Biensen et al 1998; Wilson et al 1998), and maintain
(rather than increase) placental size when adjacent foetuses
die (Vonnahme et al 2002). As a consequence, within-litter
variation in placentae size is lower in Meishans (Finch et al
2002) and foetal Meishan piglets experience less intra-
uterine competition than European breeds at equivalent
litter sizes. Meishan piglets are more physically mature at
birth, have more body fat, higher oxygen-carrying capacity
of the blood, and have better thermoregulatory abilities
relative to European breeds (Le Dividich et al 1991; Herpin
et al 1993; Miles et al 2012). Meishan piglets are also more
active and achieve a higher colostrum intake (Miles et al
2012). Meishan sows also show better quality maternal
behaviour (Meunier-Salaun et al 1991; Sinclair et al 1998),
and differences in milk composition (higher levels of milk
fat: Zou et al 1992). However, most of the comparisons with
Meishan pigs were made when White breeds were less
prolific than today and, in recent years, the difference in
© 2013 Universities Federation for Animal Welfare
Welfare implications of large litters I 207
litter size between European pig breeds and the Meishan has
decreased (Canario et al 2006a) and direct comparisons
with modern lines are scarce.
Non-genetic contributions to litter size issues
Litter size is determined by three biological factors:
ovulation rate, conception rate and embryonic/foetal
survival. Each of these factors can also be affected by a
number of non-genetic factors (Spötter & Distl 2006).
Amongst these, sow nutrition and stress could both be
important contributors to mitigating the negative conse-
quences of large litter size.
Studies suggest that sow nutrition plays an important role
in dictating piglet health and welfare outcomes. This
primarily relates to the ability of the sow to achieve the
amount of energy that is needed to support both the devel-
oping piglets and her own health and welfare, and second-
arily to different ingredients that may be added or omitted
from the feed to influence sow and piglet physiology. This
includes effects of gilt/sow nutrition before or during the
conception period. For instance, sow nutrition can impact
upon embryo survival (Ferguson et al 2006, 2007); piglet
birth weight (Musser et al 1999; Eder et al 2001; Laws et al
2009; Long et al 2010), litter uniformity (Van den Brand
et al 2006, 2009; Antipatis et al 2008; Wu et al 2010;
Campos et al 2012), piglet body energy reserves and ther-
moregulation (Herpin et al 1996), neonatal viability and
uptake of colostrum and important immune components
(Rooke et al 2001; Corino et al 2009; Leonard et al 2010),
and piglet survival (Jean & Chiang 1999; Rooke et al
2001). Sow gestational nutrition may also impact on milk
and colostrum quality directly (Farmer & Quesnel 2009).
Edwards (2005) provides a useful overview of some of the
gilt/sow nutrition work which relates to reproduction and
piglet viability. Maternal diet may also have a role in
supporting offspring welfare beyond the immediate
farrowing and lactation period (eg Oostindjer et al 2010).
One widely investigated aspect of sow gestational nutrition
is dietary fibre. Sows are feed-restricted during gestation
and may feel hungry if only fed small quantities of concen-
trate feed. Dietary fibre promotes longer feeding times and
may result in sensations of satiety (D’Eath et al 2009). In
an epidemiological study, Norwegian herds where sows
were fed a moderate (0.5–1.5 kg) amount of roughage
during gestation had lower levels of piglet mortality
compared to sows receiving no roughage (Andersen et al
2007). Sows receiving increased fibre diets during
gestation have been reported to be behaviourally calmer
during early lactation (Farmer et al 1995). However, the
outcome of experimental studies investigating gestational
dietary fibre is variable and any effects of feeding
increased levels of dietary fibre during gestation may only
become apparent over several parities (Reese et al 2008).
Maternal stress
In terms of reproductive variables, Hemsworth et al
(1981) found a strong negative relationship between sow
fear of humans and the number of piglets born per sow per
year, while Hemsworth et al (1989) found the proportion
of physical interactions with pigs that were negative was
significantly related to both total litter size and number
born alive. Furthermore, the attitude of stockhandlers on
verbal effort required to move pigs was significantly
correlated with numbers born alive. In another study, 18%
of the variation between farrowing units in the proportion
of stillborn piglets was accounted for by variation in how
sows responded to approach from an unfamiliar human
(Hemsworth et al 1999). Thus, farms using the same
genetic stock, the same nutritional strategy, with the same
housing and husbandry conditions can still vary widely in
piglet outcomes as a consequence of how gilts/sows are
handled before they ever reach the farrowing accommo-
dation. Maternal stress during gestation can lead to higher
pre-weaning mortality of live born piglets (Tuchscherer
et al 2002). Part of this is related to human behaviour and
pig fear levels interacting to influence piglet mortality.
For example, when sow fear levels are high, human
presence may be a risk factor for crushing- and savaging-
related deaths (Hemsworth et al 1995). However,
maternal stress will not only influence the sow’s
behaviour but can impair the developing piglets’ physical
and physiological characteristics.
The relationship between maternal stress and birth weight is
more complicated with different studies finding either
lowered (Haussmann et al 2000; Kranendonk et al 2006),
increased (Otten et al 2007) or unchanged (Jarvis et al
2006; Lay et al 2008; Couret et al 2009a,b; Rutherford et al
2009) birth weight under different forms, timings and sever-
ities of maternal stress. Stress during pregnancy can also
impair piglet colostrum uptake (as assessed through
immunoglobulin levels) (Tuchscherer et al 2002). There is
also the potential for trans-generational effects in relation to
piglet outcomes such as survival: gilts born to mothers that
experienced stress during pregnancy showed impaired
maternal behaviour (Jarvis et al 2006). Since maternal stress
can also act to increase offspring stress reactivity (eg
Haussmann et al 2000; Jarvis et al 2006) optimising
maternal housing may also help to minimise the stress reac-
tivity of offspring. These studies support the premise that
maternal stress during gestation could act to exacerbate
many of the problems associated with large litter size.
Therefore, close attention to gilt and sow management and
the minimisation of fear and stress in reproducing females
could help reduce some of the problems of large litter sizes.
This is discussed in more detail in a companion review
article (Baxter et al 2013).
Animal Welfare 2013, 22: 199-218
doi: 10.7120/09627286.22.2.199
208 Rutherford et al
Animal welfare implications
The different possible ways that large litter size could affect
animal welfare in pig production are summarised in Table 2.
Based on the available literature, the evidence for relation-
ships between litter size and different welfare outcomes has
been classified as speculative, uncertain, sound or strong.
Based on the possible level of welfare impact and the asso-
ciated level of certainty, each possible issue has been
assigned a level of priority for action. Although these
assessments are inevitably subjective, they allow for
attention to be focused on the most immediately important
issues in this area. In some cases, the necessary action is
further research to clarify uncertainties in how litter size and
that outcome are related, whereas for other factors the onus
is on the pig industry to act to mitigate such outcomes.
For piglets, three main areas of welfare impact were identi-
fied: piglet mortality, piglet pain and suffering, and long-
term outcomes of birth condition and early life experiences.
The most obvious welfare-relevant outcome of increasing
litter size in pigs is increased pre-natal and neonatal
mortality. Large litter size results in an intra-uterine envi-
ronment with implications for foetal development that can
have important welfare consequences in post-natal life.
Piglets born into large litters are smaller on average and
weight variability within each litter is greater.
Furthermore, the consequences of intra-uterine crowding
mean that overall piglet viability may be reduced. Piglet
mortality is certainly a central issue where societal
concern has been clearly expressed. It is also the main area
where improvements could provide a win-win scenario,
for both farm economics and animal welfare.
Data, such as those presented from Denmark in Table 1,
suggest that there has been a disproportionate increase in
pre-natal deaths compared to live-born mortality, meaning
that a significant proportion of the selection effort has
actually produced stillborn piglets. There are data relating to
the extent to which we might expect piglets to be conscious
and able to suffer that in principle allow us to make infer-
ences over the severity of the welfare insults experienced by
foetal and newly born piglets (discussed in Rutherford et al
2011). These suggest that type 1 stillbirths and an uncertain
proportion of type 2 stillbirths may not be associated with
any suffering (Mellor 2010). However, it should be noted
that this remains a challenging field of enquiry and other
alternative interpretations of awareness in foetal and
neonatal farm animals may develop with further research.
Furthermore, many piglets recorded as being stillborn may
actually have attained consciousness prior to death.
However, even if the theory that stillborn piglets are
unlikely to suffer is correct, the increased prevalence of
stillborn piglets associated with increases in litter size could
still represent a negative welfare impact on the sow, since
farrowings involving stillborn or mummified piglets may be
more uncomfortable for sows (Mainau et al 2010).
In addition to actual mortality, and possibly involving a
greater welfare impact, is the possibility that, due to being
born into larger litters, some piglets, whilst surviving the
peri-partum period, experience morbidity associated with,
for instance, a difficult birth, partial crushing, trampling or
savaging or intense teat competition. These conditions
might involve sustained or intermittent pain. Small, light
piglets are at risk of starvation as they are often excluded
by teat competition from access to productive teats and, if
they gain access to a teat, may be less efficient at stimu-
lating and draining it effectively.
Further to sources of suffering in the first few days of life,
the increased prevalence of LBW piglets may have longer
term implications for pig welfare. LBW is associated with
a range of possible detriments to welfare, including
increased stress reactivity, and increased susceptibility to
disease. Overall, the evidence suggests that LBW piglets
that survive the peri-natal period are more likely to be of
lower robustness throughout their lifetime. Thus, since
large litter size increases the proportion of LBW offspring,
more offspring in large litters will have their long-term
welfare impaired. The concept of LBW is of course
relative, for instance within rather than across breeds, and
many studies do not distinguish LBW and physical/physio-
logical maturity (ie IUGR versus SGA piglets). LBW
(defined in relation to the population distribution) can also
be statistically associated with certain outcomes without
being causally related to them (Wilcox 2001). Few studies
have properly attempted to disentangle outcomes of birth
weight and litter size and the extent to which negative
outcomes depend on absolute birth weight or weight
relative to breed or litter norm remains largely undeter-
mined. This area of pig biology requires further research to
clarify the true importance of absolute or relative birth
weight in dictating later welfare outcomes.
The biological impacts of large litter sizes on sow welfare
are more uncertain but issues related to the process of
carrying, delivering and raising a large litter, were identi-
fied. Moreover, work from other species suggests that there
are likely to be negative impacts on sow welfare.
Behavioural studies of sows in late gestation (when the
impact of litter size will be at its greatest) could identify
whether rest, resource use, social behaviour and signs of
discomfort are altered depending on subsequent litter size at
parturition. Possible impacts of litter size on the parturition
experience could also be investigated through studies of
farrowing sows. Sows may also suffer impairments to their
welfare due to the increased metabolic pressure placed on
them by selection for large litters.
Mitigating the effects of large litter sizes
Understanding pig biology may help to identify ways that the
negative consequences of large litter size could be reduced.
Genetic selection is a tool that can potentially reduce the
issues related to large litter sizes; in particular those
regarding stillborn piglets and post-natal piglet mortality.
© 2013 Universities Federation for Animal Welfare
Welfare implications of large litters I 209
Animal Welfare 2013, 22: 199-218
doi: 10.7120/09627286.22.2.199
Table 2 Summary of welfare impacts of large litter size on animal welfare outcomes for sows and piglets.
Welfare impact is an estimate of the overall effect on the individual (severity × duration) combined with the proportion of individuals affected.
Individual severity scores, based on Smulders (2009; Table 5). Score 0 (negligible): No pain, malaise, frustration, fear or anxiety; Score
1 (limited): Minor pain, malaise, frustration, fear or anxiety; Score 2 (moderate): Some pain, malaise, frustration, fear or anxiety. Stress
reaction, some change in motor behaviour, occasional vocalisation may occur; Score 3 (severe): Involving explicit pain, malaise, frustration,
fear or anxiety. Strong stress reaction, dramatic change in motor behaviour, vocalisation may occur; Score 4 (critical): Fatal, death occurs
either immediately or after some time. Physiological effects may be recorded as well as moderate behavioural change.
§See Rutherford et al (2011) for how combinations of welfare impact and uncertainty dictate suggested priority for action.
Welfare problem (proximate cause) Relationship
to litter size
Welfare impact
Priority for
Issues for offspring pigs
Stillbirths (Intra-uterine crowding; difficult birth) Strong Low 0 Medium Low
Intra-partum hypoxia (Intra-uterine crowding) Sound Medium 1 Medium Medium
Neonatal mortality (All causes) Strong High 4 High High
Neonatal mortality (Chilling) Strong Medium 4 High Medium/high
Neonatal mortality (Starvation) Strong High 4 High High
Neonatal mortality (Injury [crushing/savaging]) Uncertain High 4 High High
Neonatal mortality (LBW) Strong Medium 4 Medium Medium
Neonatal mortality (High within-litter variation in birth weight) Strong Medium 4 Medium Medium
Neonatal mortality (Disease) Sound Medium 4 Medium Medium
Neonatal pain (Injury [crushing/savaging]) Speculative High 3 Medium High
Neonatal pain (Increased teat competition) Sound Medium 2 Medium Medium
Neonatal morbidity (Disease) Sound Medium 2 Medium Medium
Neonatal morbidity (Injury) Sound Medium 2 Medium Medium
Neonatal hunger (Teat competition) Sound Medium 2 Medium Medium
Splayleg (Intra-uterine environment) Strong Medium 3 High Medium/high
Reduced play behaviour (LBW) Sound Low 1 Low Low
Increased emotionality (LBW; social interactions in large litter) Uncertain Medium 2 Medium Medium
Increased stress reactivity (LBW) Strong Medium 2 Medium Medium
Altered social behaviour (Social interactions in large litter) Uncertain Low 1 Low Low
Altered organ development (Intra-uterine crowding; LBW) Strong Low 1 Low Low
Impaired gut function (Intra-uterine crowding; LBW) Sound Medium 2 Medium Medium
Cognitive dysfunction (Hypoxia; cerebral injury) Sound Low 1 Medium Low
Impaired immune function (Intra-uterine crowding; LBW) Sound High 2 Low Medium
Issues for sows
Discomfort during gestation (Carrying a large litter) Speculative Medium 1 Low Low/medium
Poor health during gestation (Carrying a large litter) Speculative Low 1 Low Low
Hunger during gestation (Increased foetal demand for nutrients) Speculative Low 1 Low Low
Fear/anxiety during gestation (Hormonal signals of large litter) Speculative Medium 2 Low Low/medium
Pain/discomfort at farrowing (Increaased farrowing duration) Uncertain Medium 3 Medium Medium
Pain discomfort at farrowing (Increased prevalence of stillborn piglets) Sound Medium 3 Medium Medium
Dystocia (Increased farrowing duration) Sound Medium 3 Medium Medium
Infections and sickness (Tissue damage to reproductive tract) Uncertain Medium 2 Medium Medium
Fear and neophobia (Parturition pain) Uncertain Medium 2 Medium Medium
Sow fatigue (Increased farrowing duration) Uncertain Medium 2 Medium Medium
Udder damage and infection (Piglets fighting at the udder) Sound Medium 1 High Medium/high
Energetically costly lactation (Feeding piglets) Uncertain Medium 2 Medium Medium
Impaired rest during lactation (Piglet activity) Speculative Medium 1 Low Low/medium
Reduced sow longevity (Injury; fertility; lameness; agalactia) Speculative Medium 3 Medium Medium
210 Rutherford et al
Data from Denmark (Nielsen et al 2013) and The
Netherlands (Merks et al 2010) are encouraging and
suggest piglet mortality can be reduced simultaneously
with increasing litter size. Direct selection for post-natal
piglet survival has so far been seen as the most effective
strategy, but it is complex. Cross-fostering of piglets has to
be considered, but the direct genetic, maternal genetic and
maternal environmental effects are difficult to disentangle
because piglets to be fostered, stay at least for a short
period with the biological mother, and correct and precise
information on the nurse sow is often not available.
Selection for birth weight homogeneity has more potential
than selection for higher individual birth weight (English &
Smith 1975; Damgaard et al 2003) but very sophisticated
genetic statistical approaches are required (Mulder et al
2008) and this needs further research. Selection for good
maternal behaviour has been shown to be possible (Baxter
et al 2011), but it is difficult to define and to identify
suitable selection criteria. Likewise, selection for general
robustness would require identification of suitable
selection criteria, or the use of complex statistical method-
ology, such as reaction norms (Kolmodin & Bijma 2004) to
select for phenotypic plasticity of the expression of genetic
production potential (De Jong & Bijma 2002; Knap 2005).
There is, however, a lack of clarity on the effect of this
approach on survival. In the future, there is hope among
quantitative geneticists that Genomic Selection based on
high density Single Nucleotide Polymorphism arrays can
enable more efficient use of phenotypes (Mark & Sandøe
2010), for example from crossbred pigs on production
farms. However, knowledge on how and whether this can
be utilised to improve survival is still limited.
Studies of Meishan pigs (see Farmer & Robert 2003 for a
comprehensive review) support the contention that a large
litter size is not incompatible with the production of robust,
uniform, piglets. Meishan biology may suggest ways that
hyper-prolific European breeds could be adapted to allow
for better piglet outcomes at a higher average litter size. The
importance of placental function and uterine environment to
limit intra-uterine competition is clear. Equally, focusing on
genetic or nutritional interventions that improve piglet ther-
moregulatory capability in early life will improve coping
with occasional cold challenges, and support active
behaviour, and milk intake. The behavioural profile and
milk composition of sows themselves could also be
improved to support piglet survival. However, other aspects
of the pure Meishan are not suitable for the market demand
for lean meat, and the industry demand for higher growth
rates. As a consequence, partial inclusion of Meishan
genetics in some synthetic lines has been examined as a way
to gain some of the beneficial biology of the Meishans
whilst maintaining production efficiency and meeting
market demands. Inclusion of ¼ Meishan genetics in a
White composite sow line increased litter size, but
decreased piglet growth rate and lean carcase content (Hall
et al 2002). Such outcomes mean that attempts to include
Meishan genes in modern commercial hybrid females may
not be widely taken up by the industry.
Whilst genetics can help, progress via this route can take many
years and depends upon the replacement strategies of the
production herds. Over the shorter term, improvements in the
welfare status of piglets born into large litters can be achieved
through close attention to sow feeding and the minimisation of
stress. Strategies relating to the way larger surviving litters are
managed that can also contribute to improvements in welfare
are discussed separately by Baxter et al (2013).
In summary, whilst efforts to increase litter size in pig
production are expected to continue, a broader awareness of
the possible negative impacts on animal welfare of such
efforts is important. Societal acceptance of pig production
may be negatively affected if efforts are not made to
mitigate the negative welfare outcomes of increasing litter
size. However, there is good reason to think that changes
can be made in the pig industry, which could allow for
improved production performance that does not come at the
expense of good animal welfare.
Funding was provided by the Pig Research Centre,
Copenhagen, Denmark. SRUC also receives grant-in-aid
from the Scottish Government in support of improving
livestock welfare. We gratefully acknowledge the help of
Agnieszka Futro and Sheena Robson for their assistance in
producing this document and Cathy Dwyer and Susan Jarvis
for helpful comments on earlier drafts.
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... The number of pigs weaned per sow per year has risen from 20 to 30 and may reach 40 in the future (Koketsu et al., 2017). However, a large litter size causes increased piglet mortality (Rutherford et al., 2013), deteriorated maternal ability (Lund et al., 2016) and the decreased health status of the sows (Rutherford et al., 2013). Common postparturient disorders include postparturient dysgalactia (Papadopoulos et al., 2010), fever, low appetite and vaginal discharge (Tummaruk and Sang-Gassanee, 2013). ...
... The number of pigs weaned per sow per year has risen from 20 to 30 and may reach 40 in the future (Koketsu et al., 2017). However, a large litter size causes increased piglet mortality (Rutherford et al., 2013), deteriorated maternal ability (Lund et al., 2016) and the decreased health status of the sows (Rutherford et al., 2013). Common postparturient disorders include postparturient dysgalactia (Papadopoulos et al., 2010), fever, low appetite and vaginal discharge (Tummaruk and Sang-Gassanee, 2013). ...
... The results presented in this report disagreed with results from previous studies that showed that low birth weight piglets (Wolter et al., 2002;Gondret et al., 2005b) or lighter piglets at weaning (Mahan and Lepine, 1991;Wolter and Ellis, 2001;Gondret et al., 2005b) required more days compared to their heavier littermates to attain the same market weight. LBW neonates do not always remain smaller than their littermates throughout their growing period (Crume et al., 2014), and sometimes LBW piglets exhibit compensatory growth postnatally (Douglas et al., 2013;Rutherford et al., 2013;Rehfeldt and Kuhn, 2006). Consistent with previous studies (Bérard et al., 2008;2010), LBW piglets in the present study exhibited compensatory growth as differences in live weight between the different treatments disappeared by 6 weeks of age. ...
... • Injection of glucose (energy booster) [ [20], [22], [26] [17], [22] [17], [18], [19], [22] • Large litter size has consequences for uterine capacity and the post-natal life experience of piglets [27]. This review will focus on the latter. ...
Full-text available
Weaning is a critical period in the pig’s life. Piglets are confronted with abrupt changes to their physical and social environment, as well as management and nutritional changes. Weaning was always associated with a growth check and was frequently accompanied by post-weaning diarrhea in piglets. However, rapid increases in litter size, in the last decade, has increased within-litter piglet weight variation, with piglets now generally lighter at weaning, making the challenges associated with weaning even greater. Many interventions can be employed during the suckling period to ease the weaning transition for piglets. Pre-weaning strategies such as supervised farrowing (assistance with suckling, oxytocin provision), provision of pain relief to sows around farrowing, split-suckling, early oral supplementation with glucose, bovine colostrum, fecal microbiota transplantation, feed additives, solid and liquid creep feeding (milk and liquid feed) have all been investigated. The objective of these strategies is to stimulate earlier maturation of the digestive tract, improve immunity, reduce latency to the first feed post-weaning and increase early post-weaning feed intake and growth. This review focuses in particular on: 1) pain relief provision to sows around farrowing, 2) split-suckling of piglets, 3) pre-weaning provision of supplementary milk and/or liquid feed, 4) other strategies to stimulate earlier enzyme production (e.g. enzyme supplementation) and 5) other nutritional strategies to promote improved gut structure and function (e.g. L-glutamine supplementation). Correctly implementing these strategies can not only increase post-weaning growth and reduce mortality but also maximize lifetime growth in pigs.
... A large litter size has consequences for uterine capacity and the post-natal life experience of piglets [27]. This review will focus on the latter. ...
Full-text available
Weaning is a critical period in a pig’s life. Piglets are confronted with abrupt changes to their physical and social environment, as well as management and nutritional changes. Weaning has always been associated with a growth check and is frequently accompanied by post-weaning diarrhoea in piglets. However, rapid increases in litter size in the last decade have increased within-litter piglet weight variation, with piglets now generally lighter at weaning, making the challenges associated with weaning even greater. Many interventions can be employed during the suckling period to ease the weaning transition for piglets. Pre-weaning strategies such as supervised farrowing (assistance with suckling and oxytocin provision), the provision of pain relief to sows around farrowing, split-suckling, early oral supplementation with glucose, bovine colostrum, faecal microbiota transplantation, feed additives and solid and liquid creep feeding (milk and liquid feed) have all been investigated. The objective of these strategies is to stimulate earlier maturation of the digestive tract, improve immunity, reduce latency to the first feed post-weaning and increase early post-weaning feed intake and growth. This review focuses in particular on: (1) pain relief provision to sows around farrowing, (2)split-suckling of piglets, (3) pre-weaning provision of supplementary milk and/or liquid feed, (4) other strategies to stimulate earlier enzyme production (e.g., enzyme supplementation), (5) other nutritional strategies to promote improved gut structure and function (e.g., L-glutamine supplementation), and (6) other strategies to modulate gut microbiota (e.g., probiotics and prebiotics). Correctly implementing these strategies can, not only increase post-weaning growth and reduce mortality, but also maximise lifetime growth in pigs.
... However, increased litter size may also accelerate the maturation of the HPA axis in the fetuses, and the resulting higher fetal cortisol concentration may diffuse into the uterus (Rutherford et al., 2013); maternal cortisol readily crosses the placenta (Rakers et al., 2020). Hence, the original source of higher cortisol concentrations may be the mother (Hantzopoulou et al., 2022), the fetus, or both. ...
Full-text available
Stress is an important factor in animal welfare. Hair or wool cortisol concentrations are considered to be potential long-term indicators of stress experienced by an animal. Using Swifter sheep, we investigated whether ewe parity and litter size affect the wool cortisol concentrations in ewes and their offspring. We hypothesized that multiparous ewes and their offspring would have higher wool cortisol concentrations than primiparous ewes and their offspring, that ewes with larger litters and their offspring would have lower wool cortisol concentrations than ewes with smaller litters and their offspring, that male lambs would have higher wool cortisol concentrations than female lambs, and that the wool cortisol concentrations in the wool of ewes and their lambs would be correlated. Lamb wool grows in utero during the third trimester of pregnancy. In ewes, the shave–reshave method was used so that wool samples from ewes also covered approximately the last trimester of pregnancy. Our study confirmed that litter size affected ewe wool cortisol concentrations: ewes that gave birth to larger litters (i.e., 3 or 4 lambs) had higher wool cortisol concentrations than ewes that gave birth to smaller litters (i.e., 1 or 2 lambs). There was no evidence that the wool cortisol concentrations of the ewes and their lambs were correlated. Neither litter size nor parity of the ewe affected wool cortisol in the lambs. Our study confirms that wool cortisol can be reliably measured in ewes and their newborn lambs, and suggests that it may be useful as a retrospective indicator of stress during the last trimester of pregnancy.
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Increasingly hyperprolific sows and the need to reduce antibiotics represent challenges in pig farming. The aim of this work was to determine the effects of a postbiotic obtained from inactivated and stabilized whole-cells of Saccharomyces cerevisiae, administered during the sow’s gestation, on the performance of the mother and litter. Maternal feed intake, productive parameters, colostrum quality and post-weaning piglets’ health were assessed, including antibiotic consumption. The trial involved 183 sows, divided into two groups: (1) sows fed with a daily supplementation of postbiotic during gestation (n = 90); (2) sows without any supplement (n = 93). Piglets were followed up at two different post-weaning sites. The lactation efficiency of the treated sows improved by +5.9% (41.3 ± 11.4 vs. 35.4 ± 11.6%; p = 0.011). Lactating piglets’ mortality was lower in the treated group (25.1 ± 16.7 vs. 28.8 ± 14.4%; p = 0.048). The same tendency was shown in both the weaning sites, together with a reduced antibiotic consumption in weaning site 1 (0.72 ± 0.25 vs. 1.22 ± 0.30 DDDvet/PCU; p = 0.047). The results suggest the role of this postbiotic administered to the mother in improving the health status of the piglets. Furthermore, lactation efficiency is suggested as an interesting parameter for assessing the efficiency of farming.
A range of studies indicates that keeping farm animals in crowded, stressful conditions leads to an increased risk of the emergence, transmission, and amplification of pathogens including zoonoses. Some such zoonoses could lead to a pandemic. Biosecurity, though essential, is not on its own sufficient to prevent the entry of disease into large, intensive livestock housing. To minimize disease risks, both biosecurity measures and the keeping of animals in conditions that are supportive of good health and effective immunocompetence are necessary. A further threat to human health arises from the routine use of antimicrobials in intensive livestock production to prevent disease. This high use of antimicrobials contributes significantly to the emergence of antimicrobial resistance in animals, which can then be transferred to people, thereby undermining the efficacy of the antimicrobials that are so important in human medicine. If we want to save our antimicrobials and minimize the risk of future zoonoses and pandemics, we need to move to “health‐oriented systems” for the rearing of animals, systems in which good health is inherent in the farming methods rather than being dependent on the routine use of antimicrobials. Health‐oriented systems should avoid high stocking densities and large group size, should minimize stress and mixing of animals, and ensure that animals can perform their natural behaviors as the inability to do so is highly stressful. They should avoid the use of animals selected for excessive production levels as these appear to involve an increased risk of immunological problems and pathologies.
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Each suckling pig should receive ≥200 g of colostrum within the first 24 h of life, but with increased litter size this is now difficult to achieve. The aim of this study was to assess the effect of split-suckling and post-partum meloxicam provision to sows as means of ensuring adequate colostrum intake, on growth and health in pigs pre- and post-weaning. One hundred and four sows (Large White × Landrace) and their litters, averaging 16.3 piglets born alive, were assigned to one of four treatments in a two by two factorial arrangement. Factors were provision of meloxicam (yes/no; Mel/N-Mel) and split-suckling (yes/no; Split/N-Split). Meloxicam was administered intramuscularly at 0.4 mg/kg body weight to sows on release of the placenta (~2 h post-partum). Split-suckling commenced 4 h after birth of the first piglet, with the six heaviest piglets removed from the sow for 1 h to allow the lightest piglets suckle. This was repeated after 1.5 h. Pigs were weighed at birth and at day 1, 6, 14 and 27 after birth and at day 6, 14, 21, 28, 47 and 129 post-weaning. Carcass data were collected at slaughter. Medication usage was recorded from birth to slaughter. There was a split-suckling by meloxicam interaction effect at day 1-6 (P<0.001) and 6-14 (P<0.001) after birth. Meloxicam administration had no effect on average daily gain (ADG) when split-suckling was applied; however, when split-suckling was not applied, post-partum meloxicam administration increased ADG. There was a meloxicam x split-suckling interaction for ADG from weaning to day 6 post-weaning (P=0.03). Meloxicam increased ADG when split-suckling was applied but not in its absence. Carcass weight was increased by meloxicam (P=0.01) but was not affected by split-suckling (P>0.05). Meloxicam use in sows reduced the number of clinical cases of disease (P=0.04) in suckling pigs which tended to reduce the volume of antibiotics (P=0.08) and anti-inflammatories (P=0.08) administered. Split-suckling had no effect on medication usage in sows and piglets during lactation but increased their use from weaning to slaughter. In conclusion, post-partum administration of meloxicam to sows is an easily implemented strategy. It reduced clinical cases of disease, increased ADG in pigs during the first two weeks of life and early post-weaning and increased carcass weight at slaughter. However, no split-suckling benefit was observed.
Genetic selection has resulted in a considerable increase in litter size, paralleled by an increase in farrowing duration and perinatal mortality. This paper describes some of the physiological changes around farrowing, and how genetic trends and sow management interact with these. Compromised farrowing can be related to nutritional management, or to housing conditions and handling of periparturient sows. Transition diets for example, can be formulated to support calcium homeostasis and alleviate constipation. The opportunity to expression natural behaviours and minimising stress around farrowing can further optimise farrowing conditions and reduce piglet mortality. Loose farrowing systems are part of the answer to the challenges around farrowing, however, current systems do not perform consistently. In conclusion, increased farrowing duration and increased perinatal mortality may to some extent be inevitably related to trends in pig production, however, they can be improved by nutritional measures, housing conditions and farrowing management.
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The blood serum levels of glucose, hemoglobin, insulin, Cortisol, albumin, alpha-fetoprotein, alpha2-macroglobulin f and s, alpha2-antitrypsin inhibitor and alpha1-protease inhibitor were determined at birth in 5 clinically and morphologically identified mortality groups of pigs. These were compared with the levels observed in unaffected, apparently normal newborn unsuckled pigs. The blood serum profile of the pigs in the stillborn intra partum, weak, splayleg and trauma groups, respectively, as well as that of clinically normal splayleg littermates, differed significantly from that of the unaffected pigs. This was especially true for the levels of hemoglobin and the two macroglobulins. The importance of placental insufficiency causing chronic episodes of hypoxia which ultimately lead to a disturbance in organ development in the etiology of the mortality groups is discussed.
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Animal welfare has been more and more widely accepted as a scientific discipline during the last 25 years and our knowledge of animal functioning, including the extent to which they are sentient, has increased. One result of this has been that the public have demanded more legislation to protect animals and this has been passed in increasing numbers of countries but there are still many countries that do not have adequate laws protecting animals. One of the keys ways to improve animal welfare in the long term is for all those who use or have responsibility for animals to receive adequate education and training about the biological functioning of those animals, including ways in which their welfare might be made better or worse. To date, retailers’ codes of practice have had the major effect on the welfare of farm animals although both laws and codes are needed. Further scientific studies of animal welfare are also needed but it is important to develop better methodologies for the enforcement of laws and codes and to provide adequate manpower to do this. Where the impact of different factors on animal health, or any other aspect of animal welfare, is being reviewed, careful analysis should involve not only risks but also benefits. Legislators are not just risk managers and a balance has to be struck between risks and benefits in every area of legislation.
This paper reviews recently acquired information on the peripheral and central mechanisms of acute pain in general and the pain of human parturition in particular. The material is presented in two major parts. The first consists of an overview of the current concepts of acute pain and its modulation. This is intended to serve as background for the second part, which includes discussion of: the frequency and intensity of parturition pain; its mechanisms and pathways; the factors that influence its frequency and severity; the effects of parturition pain on the mother, fetus and the forces of labour and the newborn; and the influence of pharmacological analgesia.
Salmon oil (16·5 kg /t), a source of long-chain polyunsaturated n-3 fatty acids, was included in diets offered to multiparous sows during pregnancy and lactation to measure responses in pre-weaning mortality and performance of piglets in two studies. The first study, carried out under commercial conditions, included 196 sows which were offered salmon oil and control diets from immediately post service until weaning. The same diets were also offered to 10 sows per treatment from day 58 of pregnancy in a controlled nutritional study which measured the effects of salmon oil on piglet tissue fatty acid composition. Offering salmon oil to the sow significantly increased gestation length and decreased individual piglet birth weight but had no effect on litter size at birth. Overall, salmon oil reduced pre-weaning mortality from 11·7% to 10·2% mainly by reducing the incidence of deaths from crushing by the sow. More detailed analysis of mortality using a general linear mixed model and 2294 piglet records, demonstrated that the incidence of pre-weaning mortality was significantly decreased with increasing individual piglet birth weight and by inclusion of salmon oil in the diet; the incidence of mortality increased with average piglet birth weight in a litter. Salmon oil inclusion had no effect on weight of litter weaned, sow lactation food intake or subsequent reproductive performance. In both studies, dietary salmon oil increased the proportions of long-chain n-3 polyunsaturated fatty acids in colostrum to a similar extent. In the nutritional study, inclusion of salmon oil reduced the proportions of 20 : 4 n-6 in piglet liver and brain at birth and increased the proportions of long-chain n-3 polyunsaturated fatty acids. Therefore, despite reducing piglet birth weight, offering sows salmon oil reduced pre-weaning mortality of piglets. The nutritional study showed that the amount and type of marine oil used may not have been optimal.
Meishan sows are known for their high prolificity and great lactational performances. Specific breed characteristics in terms of their embryonic, foetal and placental developments as well as their differences in mammary development at the end of gestation are covered. The various known metabolic, physiological and endocrine factors related to the decreased embryonic mortality and increased placental vascularity, which are largely responsible for the greater litter size of Meishans, are discussed. An overview of published data on the endocrine status of the sow and foetuses throughout pregnancy is also presented. The superiority of Meishan sows during lactation is described in terms of its various components (i.e., piglet growth and development, sow and litter behaviour, milk composition) and the breed differences pertaining to sow metabolism and endocrinology during lactation are covered in order to provide an insight as to the possible mechanisms responsible for these superior performances. This review illustrates how a better understanding of the biological differences between Meishan sows and sows from European breeds could benefit the development of new management schemes to further improve reproductive potential of sows from traditional breeds.
Meishan sows are known for their high prolificity and great lactational performances. Specific breed characteristics in terms of their embryonic, foetal and placental developments as well as their differences in mammary development at the end of gestation are covered. The various known metabolic, physiological and endocrine factors related to the decreased embryonic mortality and increased placental vascularity, which are largely responsible for the greater litter size of Meishans, are discussed. An overview of published data on the endocrine status of the sow and foetuses throughout pregnancy is also presented. The superiority of Meishan sows during lactation is described in terms of its various components (i.e., piglet growth and development, sow and litter behaviour, milk composition) and the breed differences pertaining to sow metabolism and endocrinology during lactation are covered in order to provide an insight as to the possible mechanisms responsible for these superior performances. This review illustrates how a better understanding of the biological differences between Meishan sows and sows from European breeds could benefit the development of new management schemes to further improve reproductive potential of sows from traditional breeds. Key words: Meishan, gestation, lactation, hormones, behaviour, performance
Twenty-four published reports dating from 1975 to 2007 were examined to determine the overall effects of feeding gestation sows additional fiber. Sow and litter traits among trials were weighted by the number of litters for each treatment within each trial. Overall, sows can successfully consume high-fiber diets during gestation with few deleterious effects. Positive effects from feeding high-fiber diets were evident in litter size (0.2 to 0.6 pigs/litter) and sow lactation feed intake (0.5 to 0.8 lb/day), but they are not largely evident until the second reproductive cycle following exposure to the diet. It's possible that to ensure sow and litter performance improvements from feeding fiber, fiber must be included in the diet before mating.
The second edition of this book contains chapters that discuss modern pig genetics, including taxonomy and evolution, domestication, coat colour variation, morphological traits and hereditary diseases, immunogenetics, cytogenetics, genomics, behaviour genetics, reproduction, transgenics, developmental genetics, pig genetic resources, performance traits, carcass and meat quality genetics, genetic improvement, pigs as models for biomedical sciences, pig breeds and genetic nomenclature. This book is intended for those who study or work with pigs.