2

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 (4^oC) before and after inoculation	40%
Cold stress (4^oC) 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 32^oC or more (Lean, 1994; Curtis, 1995). Pre-nursery piglets (15 to 35kg) require from 26 to 32^oC 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 10^oC 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 44^oC. 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. Bøe (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	6.07^a	5.07^b	5.71^a,b	0.13	0.09	0.03
End of nursery weight, kg	10.6^a	11.6^b	12.0^b	0.35	0.02	0.01
ADG, 0 to 28d, kg/d	0.198^a	0.236^b	0.253^b	0.01	0.004	0.001
Feeding (head in feeder)	1.33^a	3.06^b	2.54 ^b	0.29	.0007	0.0003
Drinking (mouth on waterer)	0.67^a	0.30^b	0.27^b	0.11	0.02	0.007
Lying	83.2^a	79.1^b	81.0^a,b	1.32	0.10	0.06
Agonistic behaviors	1.52^a	0.82^b	0.96^a,b	0.24	0.11	0.04

^a,bMeans 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 (Bøe, 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 (Bøe, 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).

A major welfare problem in all farrowing systems is the level of piglet mortality (60% of all piglet deaths occur within the first 72h) with the majority of piglets succumbing to crushing by the sow and starvation (Svendsen et al., 1986; Edwards et al., 1994b; Marchant et al., 2000). Newborn piglets are highly dependent on the sow for food, protection from disease, cold and predators. Yet the sow can also be the main cause of preweaning mortality with 25% of all piglet preweaning mortality attributed to crushing (English and Wilkinson, 1982; Svendsen, 1992). The complex phenomenon of preweaning mortality has been well researched, with 30% of the losses attributable to a single factor and 70% to multiple factors (Le Dividich et al., 1996). Why sows crush and kill their young is as yet unexplained. Ethological theories relate to the sow farrowing so many young that some are dispensable. Other theories reflect that the environment or nutrient requirements are not meet, or that predators are close which can increase sow excitability (van der Steen et al., 1988). Crushed piglets not only represent one of the most important factors limiting sow productivity but also present a huge obstacle in any attempt to improve piglet well-being (Arey, 1993). The amount of time a sow spends rooting, changing her posture and the way she lays, may affect the rate of mortality in the baby piglet (Weary et al., 1996a; 1996b). Furthermore, how responsive sows are to the distress calls of their litter will be critical for piglet survival (Friend et al., 1989; Cronin and Cropley, 1991; Hutson et al., 1991; Hutson, 1993).

Several reports have compared the performance of both the intensive indoor versus outdoor farrowing systems. Bowman and Ott (1993) summarized that more piglets died in farrowing huts and open buildings (13 versus 9.7%) compared to total confinement (6.7%). Sarignac et al., (1997) compared sows housed in-groups or singularly in both indoor and outdoor environments and reported that the number of piglets born alive was not different but at weaning, indoor sows weaned more than their outdoor counterparts (9.5 versus 7.4). Berger et al., (1997) compared litters born outdoors on pasture and litters born indoors in farrowing stalls. The number of piglets born was the same (11.7) but piglet mortality was higher in the outdoors (21.1%) than in the indoor system (17.4%), which affected the average number of piglets weaned/sow/yr (21.6 versus 25.1). Mortality rates for piglets in different outdoor farrowing huts can also range. Penner et al., (1996) reported that piglet mortality was 22% in A-frames but 6% in the steel English style huts, yet little research has addressed the properties of the hut design in regards to performance achieved. Mortensen et al., (1994), van der Steen, (1994), Le Denmat et al., (1997) and Johnson et al., (2001) have all reported that a well managed outdoor unit can be as competitive as a well managed indoor unit in terms of sow and litter performance.

There are numerous structural differences between the farrowing stall and pens/pasture that impact both sow and litter behavior. In regards to the farrowing stall, it appears that the main protective effects of the farrowing stall are exerted in the first few days post partum, in that inhibited movements of the sows reduce the incidence of crushing and over-lying (Fraser et al., 1995). Detailed recordings of the movements of stalled and loose-housed sows have shown that the type of movements are altered by the design of the environment, and hence the type of crushing which occurs appears to be environment-dependent. For example loose housed sows crushed more piglets through movements where the sow rolled from side to lying on the udder or vice versa (Edwards and Malkin, 1986; Weary et al., 1996a; Marchant et al., 2001). Stalled sows crushed more piglets through movements from lying to sitting and vice versa (Bradshaw and Broom, 1999).

The stockperson’s interactions with the piglet can have very large effects on their survival, growth and welfare. While much has been written about the effects of stockpeople on mating success, relatively less work has been done on the effects of human interaction on piglet welfare. Hemsworth et al., (1995) reported data from Australia where pre-weaning mortality ranged from less than 10 to over 20% on 26 farms. These wide swings in piglet preweaning mortality can be interpreted to mean that the welfare of the piglets is equally variable. Hemsworth and Coleman (Hemsworth et a., 1995) indicate that stockperson attitude towards their piglets influences their behavior and therefore the piglets’ fear and behavior. When intervention improves the stockperson’s attitude, the farm productivity can improve.

The major welfare problem of piglet crushing was investigated by Hemsworth et al., (1995). They reported that the presence of stock people actually increased the percentage of litters that crushed piglets (Table 5). These data support the idea that, at least on some farms, the stock people can be considered not to have a positive effect on sow-piglet interactions. People may make the sows change posture more often and thus increase the risk of crushing. Clearly, the effects of humans on neonatal piglet survival and growth needs to be further studied.

Table 5. Effects of worker presence on crushing of piglets by sows. Note that when the litters were born without stock people being present, that the rate of crushing was less than half of that when the litters were born entirely during work hours. From Hemsworth et al., (1995).

Variable

Litters born entirely during work hours

Overlap period (litters start but do not finish farrowing during work hours)

Litters born entirely outside work hours

Overlap

(litters do not start but they finish farrowing during work hours)

No. litters

243

% litters with crushing

18.3

11.9

7.0

18.2

6. Conclusions

This paper has addressed numerous and complex issues that influence the welfare of the neonatal piglet. Three main categories can impact piglet welfare: litter processing, weaning and the production system. Many of the routine procedures done in the past to the neonatal piglet may not be needed. Examples of these unnecessary procedures include castration, teeth clipping, and ear notching. These “standard agricultural practices” may be performed when the welfare of the neonatal piglet or the sow becomes compromised. As pig welfare standards increase, these procedures are likely to become less common.

Weaning is a necessary management practice. While pigs could be weaned gradually by their mother, economic forces drive weaning age to younger ages. The stressfulness of weaning can be minimized by adoption of practices such as providing good nutrition and a warm, comfortable post-weaning environment complete with familiar maternal odors.

The production system that contains the neonatal piglet is less a source of welfare concern than how the animals and the system are managed. The piglet production system should attempt to minimize preweaning mortality, allow for piglet social development and be enriching for the piglet in terms of the physical environment, the social environment and its human-pig experiences.

Although the physical facility is important, the entire success of the farrowing system depends on the stockperson more than anything else – yet relatively little research has focused on stock person methods that improve piglet growth, survival or welfare. Regardless of the farrowing system and the environment, the skills (obtained by vigorous and on-going training), vigilance, patience and dedication of the stockperson is crucial.

Yet, the stockperson who can understand the neonatal piglet through observing their behavior will have a distinct advantage in adapting the thermal, physical and social environments accordingly. This will ultimately improve productivity of the farrowing unit but more importantly the well being of the baby piglet throughout their time in lactation.

7. Literature Cited

Alexander, T. J. L., K. Thornton, G. Boon, R. J. Lysons, and A. F. Gush. 1980. Medicated early weaning to obtain pigs free from pathogens endemic in the herd of origin. Vet. Rec. 106:114-119.

Algers, D. 1991. Group housing of farrowing sows – health aspects of a new system. Proc. VII Int. Cong. Anim. Hyg, Leipzig, p 851.

Algers, B., and P. Jensen. 1990. Thermal microclimate in winter farrowing nests of free-ranging domestic pigs. Livest. Prod. Sci. 25: 177-181.

American Management System (AMS). 2002. National daily hog and swine summary. Available at: http://www.ams.usda.gov/lsg/mncs/PDF_Daily/DHPS.pdf Accessed on June 26^th , 2002.

Arey, D. S. 1992. The effect of straw on farrowing site choice and nest building behaviour in sows. Anim. Prod. 54:129-133.

Arey, D. S. 1993. The welfare of pigs in confined and non-confined farrowing systems. Pig News. Inf. 14:81N-84N.

Arey, D. S., and M. F. Franklin. 1995. Effects of straw and unfamiliarity on fighting between newly mixed growing pigs. Appl. Anim. Behav. Sci. 45:23-30.

Aumaitre, A., and J. Le Dividich. 1984. Improvement of piglet survival rate in relation to farrowing systems and conditions. Ann. Rech. Vet. 15:173-179.

Barnett, K. L., E. T. Kornegay, C. R. Risley, M. D. Linderman, and G. G. Schurig. 1989. Characterization of creep fed consumption and its subsequent effects on immune response, scouring index and performance of weaning pigs. J. Anim. Sci. 67:2698-2708.

Balsbaugh, R. K., S. E. Curtis, R. C. Meyer and H. W. Norton. 1986. Cold resistance and environmental temperature preference in diarrheic piglets. J. Anim. Sci. 62:315-326.

Baxter, M. R. 1991. The freedom farrowing systems. Farm Build. Prog. 104:9-15.

Baxter, M. R., and C. E. Schwaller. 1983. Space requirements for sows in confinement. Curr. Top. Vet. Med. Anim. Sci. 24:181-199.Bel Isle, D. M., and D. C. England. 1978. Association of some individual factors and high mortality litters with porcine neonatal death. Proc. West. Sec. Am. Soc. Anim. Sci. 29:80-82.

Berger, F., J. Dagorn, M. Le Denmat, J. P. Quillien, J. C. Vaudelet, and J. P. Signoret. 1997. Perinatal losses in outdoor pig breeding. A survey of factors influencing piglet mortality. Annu. Zootechnology. 46:321-329.

Berthon, D., P. Herpin, and J. Le Dividich. 1994. Shivering thermogenesis in the neonatal pig. J. Therm. Biol. 19:413-418.

Blackshaw, J. K. 1981. Some behavioural observations in weaned domestic piglets: persistent inguinal nose thrusting, and tail and ear biting. Anim Prod. 33:325-332.

Blackshaw, J. K., A. J. Swain, A. W. Blackshaw, F. J. M. Thomas, and K. J. Gilles. 1997. The development of playful behaviour in piglets from birth to weaning in three farrowing environments. Appl. Anim. Behav. Sci. 55:37-49.

Blecha, F. 2001. Immunology. In: Biology of the Domestic Pig. (ed.) Pond, W. G and H. J. Mersmann. Cornell University Press, Ithaca, NY. pp 688-712.

Blecha, F. and D. S. Pollmann. 1983. Weaning pigs at an early age decreases cellular immunity. J. Anim. Sci. 56::396-400.

Blecha, F., D. S. Pollmann, and D. A. Nichols. 1985. Immunological reactions of pigs regrouped at or near weaning. Am. J. Vet. Res. 46:1934-1937.

Bøe, K. 1991. The process of weaning in pigs: when the sow decides. Appl. Anim. Behav. Sci. 30:47-59.

Bøe, K. 1993. Maternal behaviour of lactating sows in a loose-housing system. Appl. Anim. Behav. Sci. 35:327-338.

Bøe, K. 1994. Variation in maternal behaviour and production of sows in integrated loose housing systems in Norway. Appl. Anim. Behav. Sci. 41:53-62.

Bonnette, E. D. 1985. The effects of elevated sloped floor farrowing pens compared to conventional farrowing crates on sow and baby pig performance and behavior. Anim. Sci. Res. Rep. 4:114-117.

Bowman, G., and S. L. Ott. 1993. Comparing swine preweaning death losses between total confinement farrowing facilities and open barns and huts. Anim. Health. Insight. Winter meeting. pp 1-7.

Bradshaw, R. H., and D. M. Broom. 1999. A comparison of the behaviour and performance of sows and piglets in crates and oval pens. Anim. Sci. 69:327-333.

Brookes, J. B., and I. J. Lean. 1993. Teeth clipping in piglets. Anim. Prod. 56:437 (Abstr.).

Broom, D. M. 1993. Assessing the welfare of modified or treated animals. Live. Prod. Sci. 36:39-54.

Brown, J. M. E., S. A. Edwards, W. J. Smith, E. Thompson, and J. Duncan. 1996. Welfare and production implications of teeth clipping and iron injection of piglets housed in outdoor systems in Scotland. Prev. Vet. Med. 27:95-105.

Buchenauer, D. Parameters For Assessing Welfare, Ethological Criteria.. 1981. Curr. Top. Vet. Med. Anim. Sci. 11:75-94.

Chambers, C., L. Powell, E. Wilson, and L. E. Green. 1995. A postal survey of tail biting in pigs in south west England. Vet. Rec. 136:147-148.

Christison, G. I., N. J. Lewis, and G. R. Bayne. 1987. Effects of farrowing crate floors on health and performance of piglets and sows. Vet. Rec. 11: 37-41.

Cox, L. N., and J. J. Cooper. 2001. Observations on the pre- and post weaning behaviour of piglets reared in commercial indoor and outdoor environments. Anim. Sci. 72:75-86.

Cronin, G. M., and J. A. Cropley. 1991. The effect of piglet stimuli on the posture changing behaviour of recently farrowed sows. Appl. Anim. Behav. Sci. 30:167-172.

Cronin, G. M., G. J. Simpson, and G. J. Hemsworth. 1996. The effects of the gestation and farrowing environments on sow and piglet behaviour and piglet survival and growth in early lactation. Appl. Anim. Behav. Sci. 46:175-192.

Csermely, D. 1994. Maternal behaviour of free-ranging sows during the first 8 days after farrowing, J. Ethol. 12:53-62.

Curtis, S. E. 1985. Physiological responses and adaptations of swine. In: M. K. Yousef (ed.) Stress physiology in livestock pp 59-67. Volume II. CRC Press.

Curtis, S. E. 1995. The physical environment and mortality. In: M. A. Varley (ed.) The Neonatal Pig. Development and Survival. pp 269-285. CAB Int., Wallingford, Oxon, UK.

De Passillé, A. M. B., J. Rushen, and T. G. Hartsock. 1988. Ontogeny of teat fidelity in pigs and its relation to competition at suckling. Can. J. Anim. Sci. 68:325-338.

Duncan, I. J. H., and V. Molony. 1986. In: Proceedings of a Workshop on Assessing Pain in Farm Animals. Roslin, Scotland, 25-26 October 1984. Directorate General for Agriculture, Coordination of Agricultural Research, Commission of the European Communities, Publication EUR9742EN.

Dybkjaer, L. 1992. The identification of behavioural indicators of “stress” in early weaned piglets. Appl. Anim. Behav. Sci. 35:135-147.

Edwards, S. A., and S. J. Malkin. 1986. An analysis of piglet mortality with behavioural observations. Anim. Prod. 42: 470 (Abstr.).

Edwards, S. A., I. Riddoch, and C. Fordyce. 1994a. The effect of farrowing hut insulation on piglet survival and live-weight gain in outdoor systems. Paper presented at the 45^th Annu. Meet. EAAP., September 5-8^th, Edinburgh, UK. pp 1-5.

Edwards, S. A., W. J. Smith, C. Fordyce, and F. Macmenemy. 1994b. An analysis of the causes of piglet mortality in a breeding herd kept outdoors. Vet. Rec. 135:324-327.

Edwards, S. A., I. Riddoch, and C. Fordyce. 1995. The effect insulation in farrowing huts on the survival and growth of piglets in outdoor systems. Farm Build. Prog. 117:33-35.

English, P. R., W. J. Smith, and A. Maclean. 1977. Farrowing. In. The sow: Improving her efficiency pp 123-124. 2^nd edition. Farming Press Ltd., Ipswich, Suffolk.

English, P. R., and V. Wilkinson. 1982. Management of the sow and litter in late pregnancy and lactation in relation to piglet survival and growth. In: (D. J. A. Cole and G. R. Foxcroft (ed.) Control of mortality Pig Reproduction, pp 479-506. Butterworths, London.

English, P. R., and V. Morrison. 1984. A review of survival problems of the neonatal pig. Proc. Pig. Vet. Soc. 11:39-55.

English, P. R., V. R. Fowler, S. Baxter, and B. Smith. 1988. The growing and finishing pig: Improving efficiency. Farming Press Ltd., Ipswich, Suffolk.

Europa, 2002. Animal welfare on the farm. Avalibale at: http://europa.eu.int/comm/food/fs/aw/aw_farm_en.html Accessed on April, 5^th, 2002.

Federation of Animal Science Societies (FASS). 1999. Guide for the care and use of agricultural animals in agricultural research and teaching. 1^st rev. ed. Federation of Animal Science Societies, Savoy, IL.

Fisher, D. M. 1990. The application of electronic identification to groups of farrowing and lactating sows in straw bedded housing. In: Electronic Identification in Pig Production. RASE, Stoneleigh, p 101.

Frampton, A. V., S. E. Curtis, M. Ellis, and G. Hollis. 2000. Effect of hut design on farrowing and lactation performance of pigs housed in a hoop structure. Dept. Anim. Sci. Univ. Urbana-Champaign. Research Report pp 140-143.

Fraser, A. F., and D. M. Broom. 1997. Pig welfare problems. In: Farm animal behaviour and welfare pp 358-369. CAB INT, Norton, UK.

Fraser, D. 1978. Observations on the behavioural development of suckling and early-weaned piglets during the first 6 weeks after birth. Anim. Behav. 26:22-30.

Fraser, D. 1987a. Mineral deficient diets and the pig’s attraction to blood: implications for tail biting. Can. J. Anim. Sci. 67:909-918.

Fraser, D. 1987b. Attraction to blood as a factor in tail-biting. Appl. Anim. Behav. Sci. 17:61-68.

Fraser, D., and B. K. Thompson. 1986. Variation in piglet weights: relationship to suckling behavior, parity number and farrowing crate design. Can. J. Anim. Sci. 66:31-46.

Fraser, D., P. A. Phillips, and B. K. Thompson. 1988. Initial test of a farrowing crate with inward-sloping sides. Live. Prod. Sci. 20:249-256.

Fraser, D., P. A. Phillips, B. K. Thompson, E. A. Pajor, D. M. Weary, and L. A. Braithwaite. 1995. Behavioural aspects of piglet survival and growth. In: M. A. Varley (ed). The Neonatal Pig – Development and Survival. CAB Int., Wallingford, pp 287-312.

Friend, T., L. O'Connor, D. Knabe, and G. Dellmeier. 1989. Preliminary trials of a sound-activated device to reduce crushing of piglets by sows. Appl. Anim. Behav. Sci. 24:23-29.

Geers, R., B. Dellaert, V. Goedseels, A. Hoogerbrugge, E. Vranken, F. Maes, and D. Berkmans. 1989. An assessment of optimal air temperatures in pig houses by the quantification of behavioural and health-related problems Anim. Prod. 48:571-578.

Goetz, M., and J. Troxler. 1993. Farrowing and nursing in the group. In: E. Collins and C. Boon (eds.). Livestock Environment IV, ASAE, p 159.

Gonyou, H. W., and D. L. Whittington. 1997. Segregated early weaning. Effects of weaning at 12 days-of-age on subsequent behaviour of piglets. 3^rd Northern American Regional Mtg. Of the International Society for Applied Ethology. Lennoxville, Quebec, Canada. (Abstr.).

Hampson, D. J., M. Hinton, and D. E. Kidder. 1985. Coliform numbers in the stomach and small intestine of healthy pigs following weaning at three weeks of age. J. Comp. Pathol. 95:353-362.

Harris, M., and H. Gonyou. 1996. The birthing room: accommodation and behaviour in periparturient gilts. 31. ISAE, International Congress of the International Society for Applied Ethology.

Hatet, G., S. A. Edwards, K. Gall, and D. S. Arey. 1994. Effect of three lactation systems on sow and piglet performance and behaviour. Anim. Prod. 58:475 (Abstr.).

Hemsworth, P. H., G. J. Coleman, and J. L. Barnett. 1994. Improving the attitude and behaviour of stockpersons towards pigs and the consequences on the behaviour and reproductive performance of commercial pigs. Appl. Anim. Behav. Sci. 39:349-362.

Hemsworth, P. H., G. J. Coleman, G. M. Cronin and E. M. Spicer. 1995. Human care and the neonatal pig. In: The neonatal pig: development and survival. Ed. M. Varley. Pp. 313-331. CAB International. Oxon, UK.

Hessing, M. J. C., and M. J. M. Tielen. 1994. The effect of climatic environment and relocating and mixing on health status and productivity of pigs. Anim. Prod. 59:131-139.

Hohenshell, L. M., J. E. Cunnick, S. P. Ford, H. G. Kattesh, D. R. Zimmerman, M. E. Wilson, R. L. Matteri, J. A. Carroll, and D. C. Lay, Jr. 2000. Few differences found between early- and late-weaned pigs raised in the same environment. J. Anim. Sci. 78:38-49.

Honeyman, M. S., W. B. Roush, and A. D. Penner. 1998a. Pig crushing mortality by hut type in outdoor farrowing. Ann. Prog. Rep. Iowa State Univ. pp 16-17.

Honeyman, M. S., W. B. Roush, and A. D. Penner. 1998b. Effect of outdoor farrowing hut size on piglet mortality. Ann. Prog. Rep. Iowa State Univ. p 19.

Horrell, R. I. 1982. Immediate behavioural consequences of fostering 1-week-old piglets. J. Agric. Sci. 99:329-336.

Horrell, I., and J. Bennett. 1981. Disruption of teat preferences and retardation of growth following cross-fostering of 1-week-old pigs. Anim. Prod. 33:99-106.

Horrell, I. and J Hodgson. 1992. The bases of sow-piglet identification. 2. Cues used by piglets to identify their dam and home pen. Appl. Anim. Behav. Sci. 33:329-343.

Houszka, H. M., J. S. Strøm, and S. Morsing. 2000. Thermal conditions in a piglet nest covered in different ways. In Swine Housing Proc. First Int. Conf. October 9-11. Des Moines, IA. pp. 324-331.

Hrupka, B. J., V. D. Leibbrandt, T. D. Crenshaw, and N. J. Benevenga. 1998. The effect of farrowing crate heat lamp location on sow and pig patterns of lying and survival. J. Anim. Sci. 76:2995-3002.

Hrupka, B. J., V. D. Leibbrandt, T. D. Crenshaw, and N. J. Benevenga. 2000. The effect of thermal environment and age on neonatal pig behavior. J. Anim. Sci. 78:583-591.

Hunter, E. J., T. A. Jones, H. J. Guise, and R. H. C. Penny. 1997. A survey of the incidence and distribution of tail biting at five abattoirs. Cambac JMA Research.

Hutson, G. D. 1993. The response of sows to novel visual, olfactory, auditory and tactile stimuli. Appl. Anim. Behav. Sci. 35:255-266.

Hutson, G. D., J. L. Wilkinson, and B. G. Luxford. 1991. The response of lactating sows to tactile, visual and auditory stimuli associated with a model piglet. Appl. Anim. Behav. Sci. 32:129-137.

Jarvis, S., K. A. McLean, S. K. Calvert, L. A. Deans, J. Chirnside, and A. B. Lawrence. 1999. The responsiveness of sows to their piglets in relation to the length of parturition and the involvement of endogenous opioids. Appl. Anim. Behav. Sci. 63:195-207.

Jensen, P. 1988. Maternal behaviour and mother-young interactions during lactation on free-ranging domestic pigs. Appl. Anim. Behav. Sci. 20:297-308.

Jensen, P., and I. Redbo. 1987. Behaviour during nest leaving in free-ranging domestic pigs. Appl. Anim. Behav. Sci. 18:355-362.

Jensen, P., and B. Recén. 1989. When to wean – observations from free-ranging domestic pigs. Appl. Anim. Behav. Sci. 23:49-60.

Johnson, A. K. 2001. Behavior, physiology and performance of sows and their litters produced on a sustainable pork farm. PhD dissertation. Texas Tech University. Lubbock, TX USA.

Johnson, A. K., J. L. Morrow-Tesch and J. J. McGlone. 2001. Behavior and performance of sows and litters reared indoors or outdoors. J. Anim. Sci. 79:2571-2579.

Lawrence, A. 1987. Consumer demand theory and the assessment of animal welfare. Anim. Behav. 35:293-295.

Lay, D. C., M. F. Haussmann, H. S. Buchanan, and M. J. Daniels. 1999. Danger to pigs due to crushing can be reduced by the use of a simulated udder. J. Anim. Sci. 77:2060-2064.

Lean, I. J. 1994. Pigs. In: Universities Federation for Animal Welfare (UFAW). UFAW, Herts, UK.

Le Denmat, M., J. Dagorn, A. Aumaitre, and J. C. Vaudelet. 1997. Outdoor pig breeding in France. Porc Nuusbrief.

Le Dividich, J., P. Herpin, and P. Rousseau. 1996. How extreme environmental temperatures and nutrition affect the survival and the growth rate of piglets. Teagasc Pig Conf pp 1-12.

Leibbrandt, V. D., R. C. Ewan, V. C. Speer, and D. R. Zimmerman. 1975. Effect of weaning and age at weaning on baby pig performance. J. Anim. Sci. 40:1077-1080.

Lewis, N. J., and J. F. Hurnik. 1985. The development of nursing behaviour in swine. Appl. Anim. Behav. Sci. 14:225-232.

Lou, Z., and J. F. Hurnik. 1994. An ellipsoid farrowing crate: its ergonomic design and effects on pig productivity. J. Anim. Sci. 72:2610-2616.

Marchant, J. N., A. R. Rudd, M. T. Mendl, D. M. Broom, M. J. Meredith, S. Corning, and P. H. Simmins. 2000. Timing and causes of piglet mortality in alternative and conventional farrowing systems. Vet. Rec. 147:209-214.

Marchant, J. N., D. M. Broom, and S. Corning. 2001. The influence of sow behaviour on piglet mortality due to crushing in an open farrowing system. Anim. Sci. 72:19-28.

Martineau, G. P., J. P. Vaillancourt, and A. Broes. 1995. Principal neonatal diseases. In: M. A. Varley (ed). The Neonatal Pig – Development and Survival. CAB Int., Wallingford, pp 287-312.

National Pork Board (NPB). 2002. Swine Care Handbook. NPB. Des Moines, Iowa. USA.

McCaw, M. B., A. Holtcamp, J. Roberts, and P. Davies. 1996. McRebel management system (strictly limited cross-fostering) for controlling PRRS-associated disease losses in suckling and nursery pigs. In Proc. 14^th Int. Pig Vet. Sci. Congr. Bologna, Italy, p 67.

McGlone, J. J. 1985. A quantitative ethogram of aggressive and submissive behaviors in recently regrouped pigs. J. Animal Science. 61:559-565.

McGlone, J. J., and S. E. Curtis. 1985. Behavior and performance of weanling pigs in opens equipped with hide areas. J. Anim. Sci. 60:20-24.

McGlone, J. J., and F. Blecha. 1987. An examination of behavioral immunological and productive traits in four management systems for sows and piglets. Appl. Anim. Behav. Sci. 18:269-286.

McGlone, J. J. and J. L. Morrow. 1988. Reduction of pig agonistic behavior by androstenone. J. Animal Science. 66:880-884.

McGlone, J. J., and J. M. Hellman. 1988. Local and general anaesthetic effects on behavior and performance of 2- and 7-week old castrated and uncastrated piglets. J. Anim. Sci. 66:3049-3058.

McGlone, J. J. and J. Morrow-Tesch. 1990. Productivity and behavior of sows in level vs. sloped farrowing pens and crates. J. Anim. Sci. 68:82-87.

McGlone, J. J. and T. A. Hicks. 2000. Farrowing hut design and sow genotype (Camboroug-15 vs. 25% Meishan) effects on outdoor sow and litter productivity. J. Anim. Sci. 78:2832-2835.

McGlone, J. J., S. E. Curtis and E. M. Banks. 1987. Evidence for aggression-modulating pheromones in prepubertal pigs. Behav. Neural. Biol. 47:27-39.

McGlone, J. J. and D. L. Anderson. 2002. Synthetic maternal pheromone stimulates feeding behavior and weight gain in weaned pigs. J. Anim. Sci. (in press).

McGlone, J. J. S. E. Curtis and T. R. Houpt. 2001. Husbandry, anesthesia and surgery. In: Biology of the Domestic Pig. Ed. Pond, W. G and H. J. Mersmann. Cornell University Press, Ithaca, NY. pp 79-121.

McGlone, J. J., R. I. Nicholson, J. M. Hellman, and D. N. Herzog. 1993. Development of pain in young pigs associated with castration and attempts to prevent castration-induced behavioral changes. J. Anim. Sci. 71:1441-1446.

Meat and Livestock Commission (MLC). 1998. Pig Year book.. Milton Keynes, Meat and Livestock Commission, pp 53-54.

Metz, J. H. M., and H. W. Gonyou. 1990. Effect of age and housing conditions on the behavioural and haemolytic reaction of piglets to weaning. Appl. Anim. Behav. Sci. 27:299-309.

Ministry of Agriculture Fisheries and Food (MAFF). 1983. Codes of recommendations for the welfare of livestock: Pigs. MAFF, London.

Ministry of Agriculture Fisheries and Food (MAFF). 1996. Summary of the law relating to farm animal welfare. MAFF, London.

Morrison, V., P. R. English, and G. A. Lodge. 1983. The effects of alternative creep heating arrangements at two house temperatures on piglet lying behaviour and mortality in the neonatal period. Anim. Prod. 36:530-531.

Morrow, J. 1988. Behavioral, physiological and environmental factors in baby pig mortality. PhD dissertation. Texas Tech University. Lubbock, TX. USA.

Morrow-Tesch, J., and J. J. McGlone. 1990. Sources of maternal odors and the development of odor preferences in baby pigs. J. Anim. Sci. 68:3563-3571.

Mortensen, B., V. Ruby, B. K. Pedersen, J. Smidth, and V. A. Larsen. 1994. Outdoor pig production in Denmark. Pig News. Inf. 15:117N-120N.

Mount, L. E. 1963. Environmental temperature preferred by the young pig. Nature (Lond.). 199:1212-1213.

National Animal Health Monitoring System (NAHMS). 2000. Part I. Reference of swine health and management in then United States. CO, USA.

Newberry, R. C., and D. G. M. Wood-Gush. 1985. The suckling behaviour of domestic pigs in a semi-natural environment. Behav. 95:11-25.

Newberry, R. C., and D. G. M. Wood-Gush. 1988. Development of some behaviour patterns in piglets under semi-natural conditions. Anim. Prod. 46:103-109.

Noonan, G. J., J. S. Rand, J. Priest, and J. K. Blackshaw. 1994. Behavioural observations of piglets undergoing tail docking, teeth clipping, and ear notching. Appl. Anim. Behav. Sci. 39:203-213.

Ogunbameru, B. O., E. T. Kornegay, and C. M. Wood. 1991. Evaluation of methods of providing supplemental heat to newborn pigs during and after farrowing. J. Anim. Sci. 69:3939-3944.

Pageat, P. 2001. Pig appeasing pheromones to decrease stress, anxiety and aggressiveness. US Patent 6,169,113. Issued January 2, 2001.

Pageat, P. and Y. Teissier. 1998. Usefulness of a porcine pheromone analogue in the reduction of aggression between weaners on penning; behavioural study. Proceedings of the 15^th IPVS Congress, Birmingham, UK, July 5-9; pp. 413

Pajor, E. A., D. Fraser, and D. L. Kramer. 1991. Consumption of solid food by suckling pigs: individual variation and relation to weight gain. Appl. Anim. Behav. Sci. 32:139-155.

Peet, B. 1991. Welfare issues – a question of balance. Pigs Misset. 7:13-15.

Penner, A. D., M. S. Honeyman, and W. Roush. 1996. Pig crushing mortality by hut type in outdoor farrowing. J. Anim. Sci. 74:247 (Abstr.).

Pitts, A. D., D. M. Weary, E. A. Pajor, and D. Fraser. 2000. Mixing at young ages reduced fighting in unacquainted domestic pigs. Appl. Anim. Behav. Sci. 68:191-197.

Pittaway, M. J., and P. L. Brown. 1974. Early weaning and cage rearing. Pig Farm. 22:26-29.

Pond, W. G. and H. J. Mersmann. 2001. Biology of the domestic pig. Comstock Cornell University Press. Ithaca, NY. USA.

Price, E. O., G. D. Hutson, M. I. Price, and R. Borgwardt. 1994. Fostering in swine as affected by age of offspring. J. Anim. Sci. 72:1697-1701.

Puppe, B., and A. Tuchscherer. 2000. The development of suckling frequency in pigs from birth to weaning of their piglets: a sociobiological approach. Br. Soc. Anim. Sci. 71:273-279.

Ravel, A., S. D'Allaire, and M. Bigras-Poulin. 1996. Influence of management and the stockperson on preweaning performances according to the kind of farm. J. Rech. Porc. Fr. 28:51. (Abstr.).

Robert, S., and G. P. Martineau. 2001. Effects of repeated cross-fosterings on preweaning behavior and growth performance of piglets and on maternal behavior of sows. J. Anim. Sci. 79:88-93.

Rudd, A. R., P. H. Simmins, M. T. Mendl, and S. Malkin. 1993. Production comparisons between farrowing crates and community farrowing systems. Anim. Prod. 56:423 (Abstr.).

Rushen, J. 1987. A difference in weight reduces fighting when unacquainted newly weaned pigs first meet. Can. J. Anim. Sci. 67:951-960.

Sällvik, K., and K. Walberg. 1984. The effects of air velocity and temperature on the behaviour and growth of pigs. J. Agric. Eng. Res. 30:305-312.

Sarignac, C. N., J. P. Signoret, and J. J. McGlone. 1997. Sow and piglet performance and behavior in either intensive outdoor or indoor units with litters managed as individuals or as small social groups. J. Rech. Porcine. Fr. 29:123-128.

Scheel, D. E., H. B. Graves, and G. W. Sherritt. 1977. Nursing order, social dominance and growth in swine. J. Anim. Sci. 45:219-229.

Shimizu, M., Y. Shimizu and Y. Kodama. 1978. Effects of ambient temperature on induction of transmissible gastroenteritis in feeder pigs. Infect. Immun. 21:747-752.

Simonsen, H. B., L. Klinken, and E. Bindseil. 1991. Histopathology of intact and docked pig tails. Brit. Vet. J. 147:407-412.

Stangel, G., and P. Jensen. 1991. Behaviour of semi-naturally kept sows and piglets (except suckling) during 10 days post partum. Appl. Anim. Behav. Sci. 31:211-227.

Stanton, H. C., and R. L. Mueller. 1976. Sympathoadrenal neurochemistry and early weaning of swine. Am. J. Vet. Res. 37:779-783.

Stolba, A., and D. G. M. Wood-Gush. 1989. The behaviour of pigs in a semi-natural environment. Anim. Prod. 48: 419-425.

Straw, B. E., C. E. Dewey, and E. J. Bürgi. 1998. Patterns of cross-fostering and piglet mortality on commercial US and Canadian swine farms. Prev. Vet. Med. 33:83-89.

Suarez, S., C. Celemin,, E. Zdunczyr, E. Medina, and P. H. Williams. 1995. Aerobactin production by enterotoxigenic Escherichia coli of porcine intestine. Vet. Microbiol. 47:229-233.

Sunderland, S. 1978. Nerves and nerve injuries. 1978. 2^nd edition, Edinburgh, Churchill, Livingstone, p 377.

Svendsen, J. 1992. Perinatal mortality in pigs. Anim. Reprod. Sci. 28:59-67.

Svendsen, J., A. C. H. Bengtsson, and L. S. Svendsen. 1986. Occurrence and causes of traumatic injuries in neonatal pigs. Pig News Info. 7:159-170.

Taylor, A. A., and D. M. Weary. 2000. Vocal responses of piglets to castration: identifying procedural sources of pain. Appl. Anim. Behav. Sci. 70:17-26.

Taylor, A. A., D. M. Weary, M. Lessard, and L. Braithwaite. 2001. Behavioural responses of piglets to castration: the effect of piglet age. Appl. Anim. Behav. Sci. 73:35-43.

Thomas, P. K., and B. Holdorff. 1984. In: P. J. Dyck, P. K. Thomas, E. H. Lambert, and R. Burge (eds.). Peripheral Neuropathy, Vol II, Philadelphia, W. B. Saunders, p 1479.

Thornton, K. 1988. Outdoor pig production. Farming Press, Ipswich.

Titterington, R. W., and D. Fraser. 1975. The lying behavior of sows and piglets during early lactation in relation to the position of the creep heater. Appl. Anim. Ethol. 2:47-53.

Van der Steen, H. A. M., L. R. Schaeffer, H. de Jong, and P. N. de Groot. 1988. Aggressive behaviour of sows at parturition. J. Anim. Sci. 66:271-279.

Van der Steen, H. A. 1994. Genotypes for outdoor production. Pig News. Inf. 15:129N-130N.

Van Putten, G., and J. A. van de Burgwal. 1990. Group-housing systems for farrowing and lactating sows. IN: V. Carter and H. Carter (eds.) Group Housing of Sows. CEC, Brussels, Belgium.

Van Putten, G. 1969. An investigation into tail-biting among fattening pigs. Br. Vet. J. 125:511-517.

Van Putten, G. and I. J. A. van de Burgwal. 1990. Short communication - vulva biting in group-housed sows: preliminary report. Appl. Anim. Behav. Sci. 26:181-186.

Wallgren, P., and E. Lindahl. 1996. The influence of tail biting on performance of fattening pigs. Acta. Vet. Scand. 37:453-460.

Wattanakul, W., A. H. Stewart, S. A. Edwards, and P. R. English. 1998. The effect of cross-suckling and presence of additional piglets on suckling behaviour and performance of individually housed litters. Anim. Sci. 66:449-455.

Weary, D. M., and D. Fraser. 1997. Vocal responses of piglets to weaning: effect of piglet age. Appl. Anim. Behav. Sci. 54:153-160.

Weary, D. M., and D. Fraser. 1999. Partial tooth-clipping of suckling pigs: effects on neonatal competition and facial injuries. Appl. Anim. Behav. Sci. 65:21-27.

Weary, D. M., E. A. Pajor, B. K. Thompson, and D. Fraser. 1996a. Risky behaviour by piglets: a trade off between feeding and risk of mortality by maternal crushing? Anim. Behav. 51:619-624.

Weary, D. M., E. A. Pajor, D. Fraser, and A. M. Honkanen. 1996b. Sow body movements that crush piglets: a comparison between two types of farrowing accommodation. Appl. Anim. Behav. Sci. 49:149-158.

Webster, S., and M. Dawkins. 2000. The post-weaning behaviour of indoor-bred and outdoor-bred pigs. Anim. Sci. 71:265-271.

Wemelsfelder, F., and G. van Putten. 1985. Behaviour as a possible indicator for pain in piglets. Report B-260 of the Research Institute for Animal Production Schoonoord Zeist, Netherlands.

Weschler, B. 1996. Rearing pigs in species-specific family groups. Anim. Welf. 5:25-35.

Whatson, T. S., and J. L. Bertram. 1982. Some observations on mother-infant interactions in the pig (sus scrofa). Appl. Anim. Ethol. 9:253-261.

White, R. G., J. A. DeShazer, C. J. Tressler, G. M. Borcher, S. Davey, A. Waninge, A. M. Parkhurst, M. J. Milanuk, and E. T. Clemens. 1995. Vocalisation and physiological response of pigs during castration with or without a local anesthetic. J. Anim. Sci. 73:381-386.

Wilkinson, F. C., and J. K. Blackshaw. 1987. Do day old piglets need to have their teeth clipped? In: J. L. Barnett, E. S. Batterham, G. M. Cronin, C. Hansen, P. H. Hemsworth, D. P. Hennessy, P. E. Hughes, N. E. Johnston, and R. H. King (eds.). Manipulating Pig Production I. Australian Pig Science Association, Werribee, Australia, p 25.

Wiseman, B. S., T. W. Molitor, G. D. Dial and R. B. Morrison. 1995. Effect of segregated early weaning on performance of single source pigs. Res. Inv. Rep. NPPC, 541.

Worobec, E. K., I. J. H. Duncan, and T. M. Widowski. 1999. The effects of weaning at 7, 14, and 28 days on piglet behaviour. Appl. Anim. Behav. Sci. 62:173-182.

Worsaae, H., and M. Schmidt. 1980. Plasma cortisol and behaviour in early weaned piglets. Acta. Vet. Scan. 21:640-657.

Wyeth, G. S. F. and G. McBride. 1964. Social behaviour of domestic pigs. V. Note on suckling behaviour in young pigs. Anim. Prod. 245-247.

Zanella, A. J., D. M. Broom, and M. T. Mendl. 1991. Responses to housing conditions and immunological state in sows. Anim. Prod. 52:579. (Abstr.).

Zhou, H., and H. Xin. 1998. Responses of piglets to variable and constant wattage heat lamps with clear or red-color radiant rays. Iowa State Univ. Swine Res. Rep, pp 53-56.

End of nursery weight, kg

McGlone, J. J. and D. L. Anderson. 2002. Synthetic maternal pheromone stimulates feeding behavior and weight gain in weaned pigs. J. Anim. Sci. (in press).