Welfare of the neonatal piglet
John J. McGlone1 and
Anna K. Johnson2
1 Pork Industry Institute, Texas Tech University,
Lubbock, Texas USA (john.mcglone@ttu.edu)
2 National Pork Board, Des Moines, Iowa USA (anna.johnson@porkboard.org)
Outline
i. Abstract
1. Introduction
2. A Snap Shot of the
Biology of the Neonatal Piglet
3. Thermal Effects on
Neonatal Piglet Welfare
4. Husbandry Effects on
Neonatal Piglet Welfare
5. Production System (and
stock people) Effects on Neonatal Piglet Welfare
6. Conclusions
7. Literature Cited
i. Abstract
John J. McGlone and Anna K. Johnson. 2002. Welfare of the neonatal piglet. Nottingham Pig Science.
The subject of neonatal
piglet welfare is reviewed in the context of 15 areas that might impact piglet
welfare. Major categories include
litter processing, weaning and the production system that is used. Many litter processing procedures routinely
performed for many years are probably not absolutely necessary (including
castration, teeth clipping, tail docking and ear notching. Weaning and its associated effects on
welfare include separation from the mother, change of diet, post-weaning
fighting and transportation. Farrowing systems
and environmental impacts are considered that might impact piglet welfare. Pig
social behaviors are discussed in relation to maternal-neonatal interactions
and piglet-piglet interaction. Finally,
the role of the stockperson in providing for sound piglet welfare is
reviewed.
1. Introduction
Defining what is meant by piglet welfare can be challenging. Still, one knows adequate or inadequate welfare when it is
observed. Sick or injured piglets
clearly have poor welfare. Piglets in
an inadequate environment, while not clearly in a state of poor welfare, are at
risk to experience poor welfare. For
example, if piglets are “stressed” and have a low or suppressed immune system
(ex., very early weaned piglets), but they are not exposed to pathogens, then
they could be at risk to
experience poor welfare but are not
necessarily in a state of poor welfare at that moment. For the neonatal piglet – an animal capable
of withstanding considerable stress after day 3 of life – management of its
welfare is more about reducing the risk of welfare problems than about reducing
the situations where welfare is presently poor. For example, early-weaned (< 21d of age) piglets can be shipped over 24h in the US and they have few
health and behavioral problems when the situation is properly managed.
Which components of the environment place neonatal
piglets at risk of reduced
welfare? The primary welfare-impacting
features of the environment are the piglet’s thermal environment, its social
environment, its physical environment (the production system) and the people
who work with the piglets.
Cross-classified with these environmental components are the microbes in
the environment. Those microorganisms
or parasites that impact piglet health will have direct, negative effects on
the welfare of the neonatal piglet.
Piglet welfare can be best understood not just with the situation of the
moment, but also in the case of a future pathogenic exposure. Pathogens have far fewer effects on piglets
when the environment is adequate. For
example, if piglets are held in a warm, comfortable environment and exposed to
the Transmissible Gastroenteritis (TGE) virus, they have few signs of
illness. However, if the TGE virus is
present and the piglets are chilled, then the effects of the combined cold
stress and TGE viral exposure are very bad for the welfare of the neonatal
piglet (Shimizu et al., 1978; Table 1).
Acclimation to stress reduces but does not eliminate the illness caused
by the TGE virus. Being relatively free
from stress vastly reduces signs of illness from exposure to the TGE virus.
Table 1.
Effects of TGE exposure on piglet morbidity under thermoneutral and cold
stress conditions. All pigs were
exposed to the TGE virus and the resulting morbidity was observed. Data show an abrupt cold stress at the time
of viral inoculation causes greater illness than if the pigs have been
pre-acclimated (4 d) or if they were in a warm, comfortable environment. Adapted from Shimizu et al., 1978.
|
Treatment |
Morbidity, % |
|
Warm, comfortable
environment (30 oC) |
0% |
|
Cold stress (4oC) before and after
inoculation |
40% |
|
Cold stress (4oC) only after
inoculation |
100% |
To assess the welfare of the neonatal pig the above
components can be utilized. One must first have an appreciation of the biology
of the piglet. Then one must consider each major component of the environment
and how these components alone and in combination may impact piglet
welfare. Finally, the entire production
system must be evaluated in terms of how it might impact the welfare of the
piglet under good conditions. This
paper will focus on non-pathogenic causes of variation in piglet welfare.
2. A Snap Shot of the
Biology of the Neonatal Piglet
An understanding of the biology of the
neonatal piglet would be helpful if stockpersons are to manage or improve their welfare. The piglet can not effectively be managed by
being anthropomorphic (attributing human emotional and cognitive states to
other animals). The needs of the piglet
are strikingly different than adult humans, but interestingly not too different
from neonatal humans (Pond and Mersman, 2001).
Piglets are born with very little body
fat and very low blood levels of protective antibody in their blood (Blecha,
2001). Their visual, auditory,
somatosensory and olfactory senses are well developed at birth – they are
considered precocial (well developed at birth, in contrast to dogs, for
example). Piglets do not have the
ability to thermoregulate at birth, and are
not homoeothermic until about 48-72 h after birth. Piglets must learn where colostrum and milk
is, and to help them they have a highly developed drive to find and consume
colostrum immediately after birth. They
learn quickly and will socially interact with siblings or other animals in
their environment. Piglets are
naturally curious and they have a few
hours of energy stores that allow them to explore their environment. If they get off track – let us say they
escape the nest – they are likely to die within a few hours.
Piglets have four defense mechanisms when
confronted with a predator; hide, run, bite or squeal. They will hide from threats if the
environment allows. Among loose outdoor
piglets, they will crouch in tall grass when a threat is present. When the threat gets closer and touches them,
they will first attempt to run and return to the nest. If escape is prevented, they may bite with
their eight sharp “eye” or “needle” teeth.
Finally, when touched, they will squeal at a high pitch which especially
in the first few days will elicit help from their mother and from other
lactating sows (White et al., 1995).
The most powerful and useful sense that
piglets use within seconds or minutes after
birth is their sense of smell.
Piglets will learn their mother’s odor signature within the first 12h of
life (Morrow-Tesch and McGlone, 1990).
What’s more, by 12 h of life, the piglet can discriminate its mother’s
odor from the odor of other lactating sows (Morrow-Tesch and McGlone, 1990). This maternal odor has been characterized
and a synthetic maternal pheromone has been developed (Pageat, 2001). We are only beginning to understand how we
might manage the neonatal piglet’s olfactory environment to make the
environment more compatible with survival, growth and health.
The piglet has a strong drive to move
towards maternal odors. This drive is
much stronger than its drive to seek a warm air temperature (Morrow,
1988). Understanding the motivation of
the piglet helps stockpeople manage the environment. At this stage in the piglet’s life (especially the first 3 d), it
is better to move heat to the piglets in some way rather than hope to draw the
piglets away with warmth. It is this
olfactory attraction that is the root cause of crushing in the first 72 h of
life.
The primary cause of death after three
days is related to weak piglets. They
may be weak due to enteric or respiratory disease or lack of nutrients (low
milk production). The neonatal
environment contains enough opportunistic pathogens that the piglet needs
protection in the form of specific antibodies – antibodies found in the
mother’s blood. But another striking
feature of the neonatal piglet is that the uterine environment does not allow
efficient transfer of maternal antibodies to the piglet. The piglet is born with very low levels of
blood immunoglobulins. The level of
immunoglobulins rises over 20 mg/mL during the first hours after birth if the
piglet has access to colostral antibodies for absorption through the “open” gut
(the intestinal epithelium allows passive diffusion of large molecules for
about 24 hours after birth). Without
these immunoglobulins, the piglet’s chance of survival is much lower in
conventional production systems during the 3d to 21 d period (Blecha, 2001).
Piglets begin to fight immediately after
birth to establish a dominance order based on teat location. Front teats seem to be preferred (Wyeth and McBride, 1964). Within 24h, a teat order is formed and
European/USA piglets show strong teat fidelity (they nurse from primarily a
single teat). The social dominance
order is related to the teat order (Scheel et al., 1977).
One study was conducted evaluating indoor
and outdoor sows/litters who were managed as individuals or as a social group
during lactation and the piglet post-weaning behaviors were studied (Sarignac
et al., 1997). When indoor piglets were
mixed at weaning, the amount of fighting was considerable. When indoor litters had their partitions
removed a few days after birth and piglets become gradually acquainted, the fighting was minimal (or zero). When outdoor piglets, held on individual
paddocks were mixed at weaning, there were very few fights. The finding that outdoor piglets and
pre-acquainted piglets showed little fighting after weaning supports the idea
that post-weaning fighting among indoor piglets is an artifact of the
production system and not actually a part of normal piglet developmental
biology. Thus, while it is quite normal
for groups of piglets to have a social dominance order, it is not normal piglet
biology to have a high level of agonistic behavior at any point in their
development. In a semi-natural or
natural environment where typically there is more space and an enriched
environment, piglets become acquainted gradually and without serious agonistic
behaviors.
3. Thermal Effects on
Neonatal Piglet Welfare
Amongst the several environmental
variables that can potentially affect the welfare of neonatal piglets, the
thermal environment can be argued to be the most important. Individual newborn piglets are comfortable when the
air temperatures is 32oC or more (Lean, 1994; Curtis, 1995). Pre-nursery piglets (15 to 35kg) require
from 26 to 32oC respectively (FASS, 1999, Table 2). At birth,
piglets are poorly equipped to deal with the environment outside of the sow.
They are especially susceptible to cold stress due to a lack of coat hair, a
large surface area to body weight ratio, lack of suitable energy reserves and
poor body thermostability at birth (English and Morrison, 1984; Berthon et
al., 1994).
Table
2. Recommended air temperatures for
neonatal piglets. Minimum air
temperatures can be lowered by 10oC if bedding is provided. In drafty environments, the air temperature
should be warmer or the draft should be eliminated. Adapted from Curtis, 1985; FASS, 1999; NPB, 2002.
|
Weight of piglet, kg |
Minimum air temperature, oC |
Preferred range, oC |
|
1-3 |
25 |
32+ (in a zone) |
|
3-15 |
15 |
26-32 |
|
15-35 |
5 |
18-26 |
*
While young piglets can be maintained at temperatures as low as these minimums,
when the air temperature is below the preferred range, one should expect
behavioral, growth and health problems.
Immediately after birth, the piglet will
assume a body temperature that is similar to its environment. If it is in a mildly cold environment, the
piglet’s core temperature will drop rapidly.
To test the ability of piglets to select an appropriate temperature
Balsbaugh et al., (1986) constructed a thermocline that ranged in air
temperature from 24 to 44oC.
The piglet’s ability to select the correct temperature was not developed
until after about 48 h of life.
Balsbaugh et al., went on to show that piglets who were experimentally
dehydrated (by bacteria or concentrated sucrose gavage (feeding by stomach
tube) were even less able to select the appropriate air temperature. In fact
the dehydrated neonatal piglets incorrectly selected harmful, cooler air temperatures
and their body temperatures dangerously dropped. Thus, dehydration may cause piglets to become more cold stressed
more quickly than non-dehydrated piglets.
Furthermore, while chemically-induced
dehydration lowers body temperature, an E.
coli infection did not lower body temperature which indicates that the
combined pyrogenic (fever-inducing) and dehydration effects counter-balanced
each other (Figure 1). The combination
of enteric infection and dehydration fools the casual observer into thinking that
the piglet is healthy when in fact it has very poor welfare – and it most
likely feels poorly.
Figure
1. Effects of two methods of induced
dehydration on piglet core temperature.
Piglets given E. coli gavage
(inducing both dehydration and a pyrogenic response) did not differ in core
temperature from control piglets.
Piglets given a sucrose gavage (induced dehydration) had a significantly
lower core temperature. Adapted from
Balsbaugh et al., 1986.
Piglets who are dehydrated or have
diarrhea do not have the ability to select an environment that is as warm as
they need. Again, for the period from
birth to 48 h of life and during scours, piglets must be placed in a warm
environment and not allowed to seek other potentially more comforting olfactory
environments (ex., next to the sow) to avoid loss of body heat.
Maintaining newborn piglets at
temperatures lower than 32 oC will result in piglets mobilizing
their glycogen reserves in the liver and skeletal muscles and nutrients
supplied through the sows’ colostrum to increase their heat production.
However, if lower environmental temperatures persist then detrimental health -
and behavior-related effects will occur. The frequency of coughing and diarrhea
can increase (Sällvik and Walberg, 1984; Geers et al., 1989), piglets rapidly
become hypothermic which increases mortality and for those piglets that survive
their growth rate is negatively effected (Morrison et al., 1983; Aumaitre and Le Dividich, 1984; Arey, 1992). Litters can and will huddle and this
can effectively increase the thermal insulation and conduction (Mount, 1963; Bel Isle and England, 1978). Furthermore, day old piglets can spend
between 60 to 70% of their time budget nursing or lying inactive near the sow
(Titterington and Fraser, 1975; Lewis and Hurnik, 1985), but this makes them
vulnerable to crushing or injury by the sow. This “risky piglet lying behavior”
seems biologically understandable in that the sow provides both food and warmth
for her young (Lay et al., 1999). In addition, sow maternal pheromones attract
piglets starting at birth (Morrow-Tesch and McGlone, 1990; Weary et al.,
1996a). During the first 24h after birth piglets are still establishing their
nursing pattern and order (Hrupka et al., 1998; 2000) and therefore lay close
to the sow. Some people attempt to discourage this risky behavior by fixing
additional heat sources around the farrowing nest to entice piglets away from
the sow when resting (Hemsworth et al., 1994; Ravel et al., 1996) – but this
technique is generally not effective.
For example, Ogunbameru et al., (1991) and Hrupka et al., (1998)
provided one or more heat lamps to piglets in the front or side of the
farrowing stall. Heat lamp location had
no influence on piglet survival in both studies (although hovers lowered energy
costs without influencing piglet survival).
During the first 3 d of life,
pigs tend to lie near the sow regardless of heat lamp location or air
temperature (because the driving motivation is to be near the sow and her
olfactory signals). Use of a simulated
udder-odor to attract piglets to the odor of the mother, first suggested by
Morrow (1988) was shown to offer some promise at attracting newborn piglets
away from the sow and towards a warm area (Lay et al., 1999).
Indoor, intensive systems have solved
many of these thermoregulatory challenges by providing climatic control via
zone heating for piglets through the provisions of heat lamps and mats (Baxter
and Schwaller, 1983; Zhou and Xin, 1998). In the wild, piglets are found in a
maternally-constructed nest. The nest
is important as an area of thermal comfort and for fulfillment of behavioral
drives to build the nest. The provision
of substrates for nest building is important in alternative indoor systems for
comfort and for thermoregulation (Curtis, 1995). In outdoor systems, nest
temperatures are minimally affected by outside climatic factors (Algers and
Jensen, 1990; Houszka et al., 2000). Outdoor producers also have the option of
insulating the farrowing hut with the aim of reducing the temperature
fluctuation experienced during the year, keeping the huts cooler in the summer
and warmer in the winter. Yet the perennial questions must be based on the
value of insulating huts, specifically, whether the additional cost can be justified
in terms of improved litter performance (Edwards et al., 1994a). One UK
study (Edwards, et al., 1995) and one
USA study (Johnson, 2001) concluded that providing insulation in farrowing huts
resulted in no performance benefits, but research focused in this area is so
sporadic that a definitive answer to insulate huts can not be made at this
time.
4. Husbandry Effects on
Neonatal Piglet Welfare
It has been a long-standing assumption (largely untested) among some producers, veterinarians and researchers that neonatal animals have a reduced ability to perceive pain. This assumption is reflected in husbandry recommendations to perform routine on-farm surgical procedures such as identification, castration, tail docking, and teeth clipping within the first few weeks of life without the use of anesthetics or analgesics (Taylor et al., 2001). Although some of these procedures are no longer routinely conducted in the EU, they may be conducted if the long-term health of the sow or piglet is at risk. However there is stringent control over the methodology, timing and who can conduct the task in the UK (MAFF, 1996). Assessing pain in non-human animals is challenging but behavioral differences for example aggression fear and escape responses may be appropriate indicators of pain (Duncan and Molony, 1986). Some proponents of neonatal management argue that although these procedures do cause short term pain and discomfort to the piglet, they may provide long-term benefits to the piglet (FASS, 1999) or to the consumer.
Challenges to the welfare of the neonatal piglet
fall into three broad categories: Litter processing, weaning and production
system effects. Each of these can be
sub-divided and the results (Table 3) show that there are 15 distinct areas
that pose a risk to adequate welfare for the neonatal piglet. Each of these items can be managed to
provide what we understand at this time to be an environment that is consistent
with the welfare and the biology of the neonatal piglet.
Table 3.
Major categories and items that might pose a risk of poor welfare for
the neonatal piglet. Only the two items
with an asterisk (*) are unavoidable; all the other items are fully or
partially avoidable. All other items
can be avoided or their effects minimized through use of technologies.
|
Category |
Item |
|
Litter processing |
Ear notching/
identification |
|
|
Castration |
|
|
Tail docking |
|
|
Teeth clipping |
|
Weaning |
Separation from mother* |
|
|
Change of diet* |
|
|
Post-weaning agonistic behaviors |
|
|
Transportation after weaning -- space during transport, loading/ unloading
facilities, human-pig interactions, distance, injuries, morbidity and
mortality |
|
Production system |
High pre-weaning
mortality |
|
|
Hypogalactia or Agalactia |
|
|
Lack of social development |
|
|
Flooring-induced knee or other wounds |
|
|
Enrichment of maternal-neonatal environment |
|
|
Maternal heat or cold stress and associated piglet
effects |
|
|
Human-pig interactions |
Newborn piglets can be identified in a variety of ways with the most common and cost effective being ear notching using the universal ear notching system, which will cause some level of discomfort to the piglet. The use of tattoos and (or) tags may be better welfare for piglets but may be more costly at this time (Noonan et al., 1994).
Male piglets have their testicles removed to prevent boar taint in the meat and secondarily to reduce aggression. The prevention of boar taint has been accomplished by processing entire male pigs at a lighter weight (< 100kg) within the EU. However in the US pigs are still finished at 120kg (AMS, 2002) or more. Castration includes several events likely to be painful: scrotal incision, extraction of the testes, and severing of the spermatic cords (Wemelsfelder and van Putten, 1985; McGlone and Hellman, 1988; White et al., 1995; Taylor and Weary, 2000). Thus this procedure has been recommended to be conducted in the first week of life. There is some evidence showing a greater effect of castration on weaned piglets aged 7 to 8wks of age compared to pre-weaned piglets (< 20d; McGlone and Hellman, 1988; McGlone et al., 1993). One study by Taylor et al., (2001) reported behavioral differences between castrated and handled only piglets. In the first 2h immediately proceeding castration piglets spent more time sitting or standing inactive and less time lying. They also spent more time at the udder and less time lying in the first 22h. Castration is performed for economic reasons and infers little welfare benefit to the male piglet intended for meat consumption.
Removal of the tail (leaving no more than one-half to three quarters) has been justified to prevent tail biting later on in the production system which could result in welfare concerns for the individual piglets and economical loss to the producer at the abattoir (Hunter et al., 1997). Once the tail bleeds it becomes attractive to other piglets in the group and can result in piglet death from septicemia or cannibalism, paralysis secondary to a spinal abscess, reduced growth rate or full recovery (Chambers et al., 1995; Wallgren and Lindahl, 1996). Suggested individual (or combined) factors predisposing tail biting are numerous: overstocking, poor ventilation, breakdown in the food or water supply, poor quality diets, absence of straw the presence of wet straw and breed types (van Putten, 1969; Fraser, 1987a; 1987b; Broom, 1993). The effect of tail docking has not been extensively studied and what initiates a tail biting episode remains elusive but it is known that piglets use their tails in communication and such usage would be considerably impaired by removing most of their tail (Simonsen et al., 1991). In addition the formation of neuromas (Zanella et al., 1991) at the tip of the cut may result in spontaneous pain (Sunderland, 1978; Thomas and Holdorff, 1984), therefore, this procedure could cause short-term pain whilst being conducted and long-term pain if neuromas form.
Piglets
are born with eight fully erupted “needle teeth” (the deciduous canines and
third incisors), which the piglets use to deliver sideward bites to the faces
of littermates when fighting at the udder (McGlone, 1985; Weary and Fraser,
1999). Producers often clip these teeth to the gum line soon after birth.
Clipping teeth helps reduce facial injuries to piglets and is thought to reduce
damage to the sow’s udder. However, clipping can also reduce a piglet’s ability
to compete with litter-mates during teat disputes (Fraser and Thompson, 1986),
it exposes the pulp cavity and allows for pulpitis and gingivitis and it can
damage the gums and cause splintering of the teeth (Weary and Fraser, 1999).
Producers have three options to clipping. One is to leave the teeth intact
(Brown et al., 1996). Two is to remove the tips of the teeth with a special
grinding tool and the third is to clip only the tip of the tooth (Weary and
Fraser, 1999). Research on the value of tooth clipping has had mixed results.
Some studies have indicated significant udder damage for sows housed indoors in
stalls when piglets had intact teeth (Wilkinson and Blackshaw, 1987; Brookes
and Lean, 1993; Weary and Fraser, 1999). However Brown et al., (1996) reported
no damage to sows when housed outdoors on pasture. One study by Weary and
Fraser (1999) showed that, which ever option producers choose, the entire
litter must be clipped or not clipped otherwise piglets with intact teeth have
an advantage at the udder and will gain weight faster at the expense of their
littermates. Most large, commercial farms in the USA do not clip needle teeth
as a routine practice – they may clip the rare litter that induces sow udder or
sibling face wounds.
The practice of cross-fostering piglets
between litters is a common practice aimed at improving survival and growth of
piglets by equalizing the number of piglets per litter and minimizing weaning
weight variation. The timing of cross-fostering is critical in regard to how
successful this practice is. It is recommended that producers cross-foster
within 24h after parturition (English et al., 1977), before the
mother-offspring bond forms and the nursing order has developed (de Passillé et
al., 1988). Horrell and Hodgson (1992) demonstrated that piglets exhibited
evidence of preferring their own home environment from 11 to 18h after
parturition and this preference was well developed by 24 to 36h of age. Later
cross-fostering could result in sow aggression towards alien piglets and a
disruption of the suckling process, with the sow engaging in an increased
number of nursing cycles that she terminates before milk let down (Horrell,
1982; Wattanakul et al., 1998). Piglets that are cross-fostered at an older age
also show negative behavioral responses: they display signs of distress,
attempt to escape from the new pen, can take 10s longer from the start of
suckling to approach the udder and are less likely to be suckling at milk let
down. This behavior has been termed the “wandering-squealing” syndrome. This
reluctance to suckle can negatively effect weight gain and eventual weaning
weight (Horrell and Bennett, 1981; Price et al., 1994). Aggression between
recently mixed piglets increases (Robert and Martineau, 2001) with increased
vocalizations at the time of nursing, fighting at the udder and increased
facial lacerations on fostered piglets. Finally extensive cross-fostering
maintains a continuous cycle of pathogen transmission (McCaw et al., 1996)
which could increase preweaning mortality and post-weaning infections transmitted
through the open wounds on the piglets face. Yet even with this behavioral,
performance and health information a survey conducted in 1998 on 300 farms in
the US and Canada reported that for at least one fourth of the herds, 60% of
cross-fostering occurred after the first week of life (Straw et al., 1998).
Natural weaning in swine is a gradual
process that cannot be defined as a specific time period but is rather a shift
from reliance on the sow’s milk to a reliance on other food (Newberry and Wood-Gush, 1985; English et al., 1988; Lean, 1994).
Descriptions of sows in semi-natural environments vary with regards to when
weaning is completed. Stolba and Wood-Gush (1989) reported that piglets were
weaned at an average age of 12.5wks. Jensen and Recén (1989) reported that
weaning was not completed until 17.2wks. Bųe (1991) found that sows and piglets
housed in enriched pens had completed their weaning cycle by 12 wks. However,
such a lengthy lactation period is inefficient for modern swine production,
because the sow seldom comes into heat. In North America, weaning on commercial
swine farms has been steadily decreasing, with the majority of piglets now
weaned between 3 and 5 wks of age (Weary and Fraser, 1997), but on larger farms
the weaning age is often 17 to 20 days of age. Recently, segregated- and
medicated-early-weaning (SEW and MEW respectively) are practices used by
producers to optimize the health of the piglets, to improve feed efficiency and
growth rate and therefore to improve economic efficiency (Hohenshell et al.,
2000). Early weaning practices remove piglets from the sow between 7 and 14d of
age and isolate them in a clean facility. The use of a separate facility is to
potentially limit the transmission of pathogens from the sow herd to the piglet
herd (Alexander et al., 1980). However, the reported disadvantages of early
weaning management practices include, inconsistent growth performance
throughout the finisher stage (Wiseman et al., 1995), decreased post weaning
gain (Leibbrandt et al., 1975) and abnormal feed intake that may affect
metabolism (Pittaway and Brown, 1974).
Weaning is a traumatic event for piglets regardless of their age. The change in nutrition from a largely milk based diet to a pelleted ration effects gut local immune status and gut microflora (Barnett et al., 1989; Hampson et al., 1985). In addition changing the accommodation and mixing piglets can all have consequences on the piglets physical, nutritional (Leibbrandt et al., 1975; Stanton and Mueller, 1976) immunological (Blecha et al., 1985) and emotional status (McGlone and Curtis, 1985; Pajor et al., 1991). Weary and Fraser (1997) weaned piglets at 3, 4 and 5wks respectively and reported that younger piglets vocalized more at weaning (average of 3.6 calls/min) but the frequency for all groups fell by day four post weaning (1.6 calls/min). In contrast with this reduction in vocalization, piglets can increase their performance of certain “undesirable behaviors”, such as belly nosing (Metz and Gonyou, 1990; Dybkjaer, 1992), tail chewing (Fraser, 1987a; Broom, 1993; Worobec et al., 1999), ear sucking (Fraser, 1978; Blackshaw, 1981), flank biting (Gonyou and Whittington, 1997) and escape behaviors (Worobec et al., 1999).
Worobec et al., (1999) compared three
weaning ages (7, 14 and 28d) on piglet feeding behavior and reported that the
speed at which piglets begin to feed on solid food is an important indicator of
how well they are adapting to weaning. Piglets weaned at 7 d spent less than 1%
of their time at the feeder in the first 2 d following weaning, compared to 3%
for piglets weaned at 14d and 5% for those weaned at 28 d. Physiological differences have also been
observed. For example higher plasma
cortisol concentrations were found in piglets weaned at 3wks compared to those
weaned at 8wks (Worsaae and Smidt, 1980) and an early weaning age was found to
decrease cellular immune reactivity and these changes were suspected to affect
disease susceptibility (Blecha and Pollmann, 1983).
Weaning is a time that the piglets
experience a new environment. The
piglet’s olfactory environment post-weaning is foreign and no doubt contributes
to the stressfulness of the environment.
We discussed above the strong effect that maternal pheromones have on
piglet-sow interactions, particularly the finding by Morrow-Tesch and McGlone
(1990) that maternal pheromones regulate nursing piglet behaviors. Pageat (2001) went on to isolate skin
secretions from sows and then to develop a fatty acid mixture that is similar
in composition to sow skin secretions.
This formulation was thought to contain the essential elements of a
possible maternal pheromone. Pageat and
Teissier (1998) reported preliminary results
suggesting piglet aggressive biting was reduced by use of this synthetic
pheromone when piglets were mixed after weaning. In a more comprehensive study, McGlone and Anderson (2002)
exposed weanling piglets to maternal pheromone or a placebo control and they
measured post-weaning behavior and performance. In this study, the maternal pheromone (Suilence, Ceva Sante
Animale, Libourne, France) was applied to the feeder or the snout of weaned
piglets. Piglet post-weaning feeding
behavior was increased and agonistic behaviors were decreased (Table 4). Weight gain was also stimulated and the
piglets were about 1kg heavier four weeks after weaning when exposed to the
maternal pheromone at weaning.
Mixing unfamiliar piglets is a common
practice at weaning. Aggressive
interactions are common among piglets mixed with unfamiliar piglets (McGlone
and Curtis, 1985; Rushen, 1987) and have been observed during paired social
encounters between piglets as young as 5 d of age (Pitts et al., 2000).
Aggressive interactions may result in wounding (McGlone and Curtis, 1985) or
leg injuries (Hessing and Tielen, 1994).
Hohenshell et al., (2000), indicated that although some behavioral
differences were evident in early weaned (10d) piglets in regards to more time
play fighting and manipulating conspecifics than later weaned piglets (30d),
overall most differences found between the two groups were evident after
weaning but disappeared before slaughter.
Agonistic behaviors can be reduced by use
of boar odor among prepubertal piglets.
McGlone et al., (1987) showed that the odor of dominant pigs reduced
agonistic behaviors in other weaned piglets.
McGlone and Morrow (1988) applied even very low concentrations of
5-alpha-androstenone to piglets and reduced post-weaning agonistic behaviors by
over 80%. However, this compound had
regulatory issues with its use (it is a blood hormone) and therefore was never
commercialized. The maternal pheromone
(Morrow-Tesch and McGlone 1990; Pageat, 2001), shown to reduce fighting in the
weaned piglet (Table 4; McGlone and Anderson, 2002) however, is a natural
product and has no regulatory issues.
The maternal pheromone is probably a more natural (and perhaps
comforting) experience for the piglet where the odor of the adult male is more
likely to be a supranormal stimuli.
Use of the maternal pheromone in the newly-weaned pig also will
stimulate feeding behavior (Figure 2) and post-weaning weight gain (Table 4).
Figure 2. Effects of a maternal
pheromone on post-weaning feeding behavior of piglets during the 48-hour
post-weaning period. Maternal pheromone
applied either to the feeder or the piglets’ snout increased feeding behavior (P < 0.01) compared with the placebo
control. Data are adapted from McGlone
and Anderson (2002); see also Table 4.
Table
4. Effects of a maternal pheromone
applied either to the feeder or directly on the piglets’ snout on post-weaning
body weights, average daily gain (ADG) and behavior. From McGlone and Anderson, (2002).
|
|
Treatments |
|
|
|
||
|
Measure |
Control |
Pheromone Feeder |
Pheromone Snout |
SE |
P-value* |
P-value contrast* |
|
Number
of piglets |
48 |
48 |
48 |
. |
. |
. |
|
Number
replicates |
16 |
16 |
16 |
. |
. |
. |
|
Weaning
weight, kg |
6.07a |
5.07b |
5.71a,b |
0.13 |
0.09 |
0.03 |
End of nursery
weight, kg
|
10.6a |
11.6b |
12.0b |
0.35 |
0.02 |
0.01 |
|
0.198a |
0.236b |
0.253b |
0.01 |
0.004 |
0.001 |
|
|
Feeding (head in feeder) |
1.33a |
3.06b |
2.54 b |
0.29 |
.0007 |
0.0003 |
|
Drinking (mouth on waterer) |
0.67a |
0.30 b |
0.27 b |
0.11 |
0.02 |
0.007 |
|
Lying |
83.2a |
79.1b |
81.0a,b |
1.32 |
0.10 |
0.06 |
|
Agonistic behaviors |
1.52a |
0.82b |
0.96a,b |
0.24 |
0.11 |
0.04 |
a,b Means with a different superscript differ, P < 0.05.
* The probability value (P-value) refers to the treatment
effect from the analysis of variance.
The P-value contrast uses a linear contrast to compare the
control with the combined treatments in which the pheromone was applied. In general, the pheromone was equally
effective when applied either to the feeder or the pigs’ snout.
Rearing conditions for piglets may have
long-term effects on social relationships that piglets are able to form (Newberry and Wood-Gush, 1988).
For example it has been reported that indoor born and raised piglets
display greater activity at the udder and suckle more compared to outdoor born
piglets (Sarignac et. al., 1997). At
weaning to day one post weaning, Webster
and Dawkins, (2000) and Cox and Cooper (2001) observed that outdoor-bred
piglets were observed to feed more than their indoor counterparts. In addition, Cox and Cooper, (2001) observed that indoor-born piglets were
more likely to engage in agonistic encounters compared to those born outdoors
but nose contact, belly nosing and tail biting were not different. These differences in agonistic behaviors
could be related to the piglets’ social experiences. Outdoor piglets can interact with alien piglets of different ages
and sizes and the quality of the interaction may be different, with outdoor piglets
having more space to resolve conflicts.
Consequently following weaning, the outdoor-born piglet may be able to
establish hierarchies without resorting to aggressive encounters. Play
behavior has not been described in detail for piglets (Blackshaw et al., 1997)
but play may be a sensitive indicator for assessing the well-being of young
piglets (Buchenauer, 1981). For
example, Worsaae and Schmidt (1980) reported a negative correlation between
plasma cortisol level and playful behavior fighting and running in piglets and
Lawrence (1987) suggested that farming systems could ensure good well-being
standards by allowing or enabling play behaviors. The definition of play differs between researchers, but most
agree that piglets engaged in mock combat, hop, scamper, pivot, toss head,
pivot, shake object and carry object (Worsaae and Schmidt, 1980; Newberry and
Wood-Gush, 1988). Newberry and
Wood-Gush (1988) studied piglet playful behavior from birth to 14wks for
piglets kept under semi-natural conditions and overall piglets engaged in more
play behavior between 2 and 6wks of age.
5. Production System (and
Stockperson) Effects on Neonatal Piglet Welfare
There are a variety of production systems
and environments that can house the neonatal piglet (MAFF, 1983). Currently,
the majority of piglets are born and reared in farrowing stalls (NAHMS, 2000),
but EU legislation will phase out this system by 2012 (Europa, 2002). Therefore, it is timely to address how
alternative farrowing systems that allow increased sow mobility may effect
neonatal piglet welfare (MLC, 1998; Bradshaw and Broom, 1999).
Producers have a choice of which
farrowing systems to implement and their decision will be based on a multitude
of factors, for example retrofitting and capital cost, labor input, and ease of
management (Peet, 1991). Producers can
house the farrowing sow and piglets indoors. One system is a group farrowing
system where sows share a communal area and piglets are confined to their nest
by some sort of barrier (Arey and Franklin, 1995; Wechsler, 1996). These include simple nest boxes (Fisher,
1990; Algers, 1991), small square nest pens with heated creeps (van Putten and
van de Burgwal, 1990; Goetz and Troxler, 1993) or specially designed highly
sophisticated nests such as the Freedom Farrowing system (Baxter, 1991). A second indoor option is the pen system
which confines individual sows but allows her some restricted movement (Bųe,
1994). Examples of pen systems are turn
around stalls (McGlone and Blecha, 1987), Ottawa stalls (Fraser et al., 1988),
ellipsoid stalls (Lou and Hurnik, 1994), slope floor pens (Bonnette, 1985;
McGlone and Morrow-Tesch, 1990) and farrowing boxes and these options can have
bedded or perforated flooring. Outdoors, sows can farrow on pasture (Thornton,
1988) using a variety of farrowing hut designs. The two most popular designs
are the A-frame and English style arcs (Honeyman et al., 1998a; 1998b). The English-arc design clearly reduced piglet mortality compared
with a straight-sided American hut design (McGlone and Hicks, 2000). With good stock people the preweaning
mortality can be similar indoors and outdoors as shown by Johnson et al.,
(2001) in a controlled study. Heat
stress in the outdoor unit does increase piglet mortality and during the warmer
months productivity may be better in indoor units for reasons not yet
understood (Johnson, 2001).
Regardless of the system and (or)
environment, baby piglet management should start before the piglets are born
through a clean, disinfected and dry farrowing area. Outdoor cleanliness can be
achieved by allowing the land to rest and by exposing the internal farrowing
hut surfaces to the sunlight for several days prior to piglet arrival. As neonatal piglets are born with a poor
immunity system, a disease challenge can be extremely detrimental to their
welfare, growth and productivity (Christison et al., 1987; Martineau et al.,
1995; Suarez et al., 1995).
During farrowing the newborn piglet can
face potential savaging and cannibalism by the sow. Although the original function of such behavior is defense of the
piglets, it can be a practical problem when the behavior is directed either at
the stockperson or at the piglets themselves (Harris and Gonyou, 1996; Fraser and Broom, 1997). Cronin et al.,
(1996) and Jarvis et al., (1999) suggested that this behavior occurs more
frequently when gilts are housed in restrictive environments, however we have
observed gilt and sow cannibalism of piglets in our outdoor unit at Texas Tech
University. The stockperson should take
a proactive role by restraining cannibalistic gilts or sows until all piglets are
born and have nursed, or piglets that are being targeted by her aggression can
be cross-fostered.
Once the sow has farrowed, she usually
remains in the nest for over 90% of her time during the first 48h after birth,
lying and nursing cyclically (Jensen and Redbo, 1987; Jensen, 1988; Csermely,
1994). Sow and litter behavior will be crucial for piglet survival (Cronin et
al., 1996), for example piglets which choose to lye close to their mother for
warmth will have a higher risk of being crushed (Bradshaw and Broom, 1999).
Some behaviors performed by the sow may be problematic for piglets. For
example, in alternative farrowing systems that have some form of a barrier to
confine piglets to the nest area but allow the sow unrestricted movement can
result in early nest abandonment (Whatson and Bertram, 1982; Newberry and Wood-Gush, 1985; Puppe and Tuchscherer, 2000). Stangel and Jensen (1991) showed that
sows in group housing systems began to abandon the nest between days 6 and 7
post partum and authors suggested that this barrier could effect the suckling
frequency. Reduced nursing could result in a slower growth rate, reduced vigor
and increased piglet mortality (Bųe, 1993; Rudd et al., 1993). Therefore,
restricting piglets to the nest for the first week of life reduces milk
stealing and allows bonding between mother and offspring (Van Putten and van de
Burgwal, 1990). Once the sow abandons the nest it is essential that the barrier
is removed (Frampton et al., 2000; Marchant et al., 2000). Caution should be
exercised by not mixing all litters at the same time because sudden mixing can
lead to problems with cross suckling (Hatet et al., 1994).