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

May 2013
Animal Welfare 22(2):199-218

DOI:10.7120/09627286.22.2.199

Authors:

Kenneth M D Rutherford

Scotland's Rural College

Emma M Baxter

Scotland's Rural College

Richard B D'Eath

Scotland's Rural College

Show all 13 authorsHide

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.

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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

factors

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: kenny.rutherford@sruc.ac.uk

Abstract

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

Introduction

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

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

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

Gestation

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.

Parturition

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

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

Denmark

Live born 11.2 11.3 11.5 11.7 11.9 12.1 12.3 12.6

Stillborn†0.9 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

Stillborn†0.8 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

Denmark

Live born 12.9 13.2 13.5 13.6 14.0 14.2 14.5 14.8

Stillborn†1.5 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

Stillborn†0.8 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

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.

Nutrition

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

Discussion

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.

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

impacts†

Individual

severity‡

Welfare impact

certainty

Priority for

action§

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.

Acknowledgements

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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PIGLETS HYPOTROPHY IN INDUSTRIAL PIG PRODUCTION. Part 1

Article

Dec 2021

Ромазан Закарьянович Сиразиев

Анализ доступной отечественной и зарубежной литературы, начиная с 50-х годов ХХ столетия до 21 года ХХ1 века, показывает, что при разведении свиней используются разные комплексы селекционных признаков, но наиболее сложной проблемой остается отбор по воспроизводительным качествам, базирующимся на многоплодии, продуктивности свиноматок по численности и качеству потомства, лактационной способности, возрасте хозяйственного использования и количестве опоросов. Многоплодие свиней - один из основных репродуктивных и производственных показателей, отражающих современную гиперплодовитую модель ведения свиноводства и экономическую эффективность отрасли. Однако с увеличением количества поросят в приплоде уменьшается однородность и масса гнезда. При этом вес поросят при рождении является важным функциональным и производственным тестовым критерием жизнеспособности (выживаемости) в подсосное время, сохранности в предотъемный и постотъемный возрастные периоды, конверсии корма среднесуточными приростами и совокупной потенциальной продуктивности. Особую актуальность решение этих вопросов приобрело в условиях интенсификации свиноводства на промышленной основе. В приплоде свиней обнаруживаются нормотрофные (полноценные, крупноплодные), гипотрофные (низковесные, маловесные, мелковесные) и мертворожденные поросята. По нашим наблюдениям между плодовитостью и количеством гипотрофных поросят выявлена прямая тесная положительная корреляция (r = + 0,98). Чем больше поросят в приплоде, тем сильнее нарастает численность мелковесных. Количество маловесных поросят меньше, когда новорожденных в гнезде насчитывается 2-6 (3,7±2,08%), но достоверно увеличивается с укрупнением приплода при 7-11 (13,3±1,17%) и 12-16 (18,0±1,39%) поросятах, а при 17-21 они занимают более трети приплода (31,7±7,27%). Analysis of available fatherland and foreign literature, starting from the 50-th years of the ХХ century to the 21 years of the XXI century, shows that different complexes of selection features are used in the breeding of pigs, but the most difficult problem remains the selection of reproductive qualities based on multiple fertility, productivity of sows in terms of number and quality of litter, lactation ability, age of economic use and number of farrowings. The multiplication of pigs is one of the main reproductive and production indicators reflecting the modern hyper-fertile model of pig breeding and the economic efficiency of the industry. However, with an increase in the number of piglets in the litter, the uniformity and mass of the littering decreases. At the same time, the weight of piglets at birth is an important functional and production test criterion for viability (survival) in sucking time, preservation in the pre-weaning and post-weaning age periods, feed conversion by average daily increases and total potential productivity. The special of these issues has acquired particular relevance in the conditions of intensification of pig production on an industrial basis. In the litter of pigs are found normotrophic (full-, large-fruited), hypotrophic (low-weight, low-weight, small-weight) and stillborn piglets. According to our observations, a direct close positive correlation (r = + 0.98) was revealed between fertility and the number of hypotrophic piglets. The more piglets in the litter, the stronger the number of small-weighted ones increases. The number of low-weight piglets is the smallest, when the number of newborns in the litter is 2-6 (3.7 ±2.08%), but significantly increases with the enlargement of the litter at 7-11 (13.3 ±1.17%) and 12-16 (18.0± 1.39%) piglets, and at 17-21 - they occupy more than a third of the litter (31.7± 7.27%).

Classification of Sows for Longevity Based on Total Number of Piglets Born Alive in the First Parities

Article

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Nov 2024
BRAZ ARCH BIOL TECHN

Hygienic Floor Management Using Hot Water: A Strategy to Reduce Piglet Mortality in Northeastern India

Article

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Sep 2024

Background: Pig farming is crucial for the agricultural economy in Northeastern India; yet high piglet mortality remains a significant issue. This study investigates the impact of hot water treatment on floor hygiene in farrowing pens to address this challenge. Methods: Thirty-six Hampshire piglets were divided into two groups: a control group with untreated floors and a treatment group with floors cleaned biweekly with hot water at 70°C. Growth performance, feed intake, Feed Conversion Ratio (FCR), incidence of diarrhea, and mortality rates were assessed. Results: Results indicated that piglets on hot water-treated floors exhibited slightly higher body weight gains and improved FCR compared to the control group. Diarrhea incidence was lower in the treatment group, which also had no mortality, while the control group experienced an 11.1% mortality rate. Conclusion: The study concludes that hot water treatment effectively enhances piglet health and growth, suggesting its potential as a valuable management practice in pig farming. Further research with varied treatment frequencies is recommended.

The impact of parity, litter size and birth weight variations within a litter on piglet pre-weaning performance

Article

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Jul 2024
CZECH J ANIM SCI

Sows are selected for their prolificacy. Therefore, assessing difficulties that can be associated with large litters is crucial. This review aims to highlight the factors that can affect reproductive performance such as breed, parity, litter size, environment, and nutrition. Understanding these factors can help producers make informed decisions about sow management and other aspects. Higher within-litter variation is the result of a high number of piglets born. It has been determined that large litter sizes pose a risk to animal welfare in the pig industry. Moreover, large litters bring more piglets with low birth weight leading to high pre-weaning losses. Lighter litter mates struggle to get enough colostrum due to the competition with heavy litter mates, which lowers their chances of survival causing high mortality. Larger litters may cause greater stress and discomfort of the sow. Therefore, applying stress-free environment and treating the sow with anti-inflammatory compounds may enhance the sow performance and consequent survival of piglets. The litter size is positively correlated with the variation in birth weight within a litter, while the average weight at birth is negatively related to litter size. Producers should therefore focus on potential management strategies that can improve piglet performance, survival and welfare such as proper supervision and adequate colostrum intake. This review highlights the historical development of the pig industry and literature on the variation in piglet weight at birth within a litter, factors influencing weight at birth, and the potential effects on the piglet performance before weaning. Also, the difficulties amongst large litters and possible strategies for managing survival in large litters were also reviewed.

Effect of Pig Domestication on Skeletal Muscle Development, Microstructure, and Genetic Mechanism Involved in Myofibre Type Formation

Chapter

Full-text available

Jul 2024

The wild boar and modern highly selected pigs are phenotypically distant European pig breeds reared in contrasting conditions and present ideal model to better understand the mechanisms behind meat quality deterioration related to domestication and selection pressure, which provoked substantial modifications in the ontogenic development as well as contractile and metabolic properties of skeletal muscles. The skeletal muscle of domestic pigs are less mature at birth and contains a lower number of myofibres compared to wild boars; however, expansive myofibre hypertrophy, protein accretion as well as additional myofibre formation are accelerated in the early postnatal period in some muscles in domestic pigs. A comparative view of the cellular and subcellular mechanisms underlying the skeletal myofibre development could help to design a breeding program that would improve the balance between the growth performance, muscularity and meat quality. This chapter therefore outlines the influence of domestication on myofibre formation and differentiation during growth and provides a comparative view on the developmental expression pattern of the MyHC isoforms, the activity of different metabolic enzymes, and the expression of selected genes responsible for the metabolic diversity of the myofibres. Additionally, there is a special emphasis on the type, composition, and histomorpho-logical traits of myofibres.

ABCD4 is associated with mammary gland development in mammals

Article

Full-text available

May 2024
BMC GENOMICS

Background Mammary gland development is a critical process in mammals, crucial for their reproductive success and offspring nourishment. However, the functional roles of key candidate genes associated with teat number, including ABCD4, VRTN, PROX2, and DLST, in this developmental process remain elusive. To address this gap in knowledge, we conducted an in-depth investigation into the dynamic expression patterns, functional implications, and regulatory networks of these candidate genes during mouse mammary gland development. Results In this study, the spatial and temporal patterns of key genes were characterized in mammary gland development. Using time-series single-cell data, we uncovered differences in the expression of A bcd4, Vrtn, Prox2, and Dlst in cell population of the mammary gland during embryonic and adult stages, while Vrtn was not detected in any cells. We found that only overexpression and knockdown of Abcd4 could inhibit proliferation and promote apoptosis of HC11 mammary epithelial cells, whereas Prox2 and Dlst had no significant effect on these cells. Using RNA-seq and qPCR, further analysis revealed that Abcd4 can induce widespread changes in the expression levels of genes involved in mammary gland development, such as Igfbp3, Ccl5, Tlr2, and Prlr, which were primarily associated with the MAPK, JAK-STAT, and PI3K-AKT pathways by functional enrichment. Conclusions These findings revealed ABCD4 as a candidate gene pivotal for regulating mammary gland development and lactation during pregnancy by influencing PRLR expression.

Challenges and opportunities for swine nutrition

Conference Paper

Full-text available

May 2024

Daniel Columbus

The issues facing pork producers and swine nutritionists moving into the future are similar to what they have been for decades, a need to increase productivity while meeting increasing demands from legislation and consumers to ensure economic, environmental, and social sustainability. While the challenges are the same, the methods with which we tackle these issues are evolving, and nutritional sciences will necessarily include additional aspects, such as physiology, metabolism, and microbiome, among others, to advance the field. There will also be a shift in focus to consider not only the impact of nutrition on growth, but on animal health and welfare as well, and to incorporate the impact of feed decisions on the environmental impact, and specifically the carbon footprint, of pork production. Our understanding of the complex interactions of the competing and symbiotic relationships between feedstuffs and animals as well as the incorporation of advancing technology, such as improved growth models and precision feeding, will be crucial for the advancement of the industry.

Chemical Composition of Newborn Piglets with Different Weights at Birth in Sows with a High Reproductive Performance

Article

Full-text available

May 2024

The present study aimed to quantify and update the data on the body composition (energy nutrients) of newborn piglets of different body weights at the time of birth, as well as of the placenta mass. Data were collected from newborn piglets (n = 25) from modern genetic lines which were stillborn or died within the first 24 h of life after being crushed to death with various body weights at birth (<0.8 kg (n = 5); 0.8–1.2 kg (n = 5); >1.2–1.6 kg (common birth weight, n = 10) and >1.6 kg (n = 5)). The placenta (n = 20) of sows from a conventional breeding farm were collected, too. The body composition of newborns of “normal” (>1.2–1.6 kg) and even lighter (0.8–1.2) weights still indicated a “normal” composition. In the case of a lower body weight of piglets <0.8 kg at birth, the crude ash (24.1%) and crude protein (8.21%) contents were higher, but the crude fat (16.1%), carbohydrate (57.4%), and gross energy (3.60%) contents were lower. The placental composition in comparison to the piglet body composition was characterized by higher crude protein contents (24.3%) and lower crude ash (31.6%), crude fat (9.08%), and carbohydrate (55.6%) contents. In conclusion, the energy and protein accumulation in the total mass of fetuses and placentas increased by 75% and 64%, respectively, in comparison to times in which the litter size varied around 10–12 piglets, essentially as a result of the larger fetal mass and not of a different body composition.

Implications of Commercial Cross-Fostering in Large Litters when Low Body Weight of Piglets is the Main Criterion

Article

Oct 2024
LIVEST SCI

Stimulating prepartum nest-building behaviour through alternative nesting materials has impacts on farrowing kinetics and maternal characteristics in crated sows

Article

Jun 2024
APPL ANIM BEHAV SCI

Blood Serum Characteristics of Newborn Pigs: Comparison of Unaffected Pigs with Pigs Belonging to Five Mortality GroupsBlod serum parametre hos nyfødte grise: En sammenligning mellem normale grise og grise fra 5 forskellige mortalitetsgrupper.

Article

Full-text available

Sep 1991
ACTA VET SCAND

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.

Animal welfare and legislation.

Chapter

Full-text available

Dec 2009

Donald M. Broom

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.

Preweaning survival in swine

Article

Full-text available

Jan 2002

Pain of Parturition

Article

Jan 1986

John J. Bonica

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.

The effect of feeding salmon oil to sows throughout pregnancy on pre-weaning mortality of piglets

Article

Dec 2001

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.

Hormonal, behavioural and performance characteristics of Meishan sows during pregnancy and lactation

Article

Mar 2003
CAN J ANIM SCI

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.

Hormonal, behavioural and performance characteristics of Meishan sows during pregnancy and lactation

Article

Mar 2003
CAN VET J

C. Farmer and S. Robert

Some causes of death in neonatal piglets

Article

Jan 1995

Dietary Fiber in Sow Gestation Diets - An Updated Review

Article

Jan 2008

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.

Genetic improvement of the pig

Article

Jan 2011

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.

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