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Pigs: Behavior and Welfare Assessment
Pigs: Behavior and Welfare Assessment J. Deen, University of Minnesota, St. Paul, MN, USA ã 2010 Elsevier Ltd. All rights reserved.
Current Uses of Behavior to Determine Welfare Status Introduction The welfare of farmed animals has received increased attention in the recent times. Compromised welfare leads to reduction in productivity. Additionally, market forces can be negative when the welfare is shown to be poor. Thus, compromised animal welfare affects the economic sustainability of animal agriculture in more than one way. However, from the producers’ perspective, there is considerable difficulty in demonstrating that adequate welfare has been ensured. The major reason for this is the lack of objective and scientific tools to evaluate animal welfare. Without objective quantification, a compromise in welfare cannot be approved nor can the efficacy of corrective measures assessed. Animal welfare involves several factors, many of which are influenced by factors other than threats to welfare. Nevertheless, behavioral changes are the first and obvious indicators of compromised welfare in animals, though the identification of the same requires thorough knowledge about the normal behavior of the species concerned. The aim of this article is to explain the importance of behavior in swine welfare assessment. Importance of Behavior in Animal Welfare Assessment Animal welfare is a multidisciplinary concept. Behavioral, physiological, and hormonal indicators are employed to assess the welfare of animals. Among these disciplines, the study of animal behavior is an important component. A major reason for the prominence of behavior as a tool in welfare assessment is that changes in behavior patterns are among the most rapid and visible responses of an animal to changes in its environment. Behavior is the way in which the animal expresses its basic needs, deficits, and happiness in an environment. The study of behavior (ethology) involves not only what an animal does but also when, how, why, and where the behavior occurred. Understanding animal behavior is the best way to know whether we are keeping the animals appropriately. The behavior of an animal is influenced by both the structure and function of the animal as well as by the interaction of the animal with the external environment. All categories of pigs under farm conditions are exposed to different types of challenges to their welfare. These challenges vary depending on different aspects of
farming such as routine management, housing, slaughter, and transport. The major welfare concern associated with housing is close confinement in barren environments. The significance of animal welfare is associated with an animal’s adaptive response to stress and its impact on biological functioning. The first response to stress is an alteration in behavior in order to cope with the stressful environment. This may or may not be accompanied by changes in physiological parameters such as respiration and/or heart rate to support the coping efforts. In many instances, it is possible to objectively assess the changes in physiological responses. However, the difficulty is in using the physiological changes alone to identify or quantify the compromise in welfare as many of the physiological parameters are influenced by factors not necessarily threats to the welfare. Therefore, a system evaluation, using a multidisciplinary approach, has been suggested to be the ideal way to assess animal welfare. By nature, each species has its own unique behavioral repertoire (the ethogram) to cope with problems in its natural environment. Scientific studies in farm animals under seminatural conditions have indicated only meager changes in their behavioral repertoire despite domestication. This is the major reason for the widespread consensus that animals should be able perform their natural behavior in order for their welfare to be at a high level. Thus, animal welfare is often defined in terms of natural living or normal functioning of behavioral systems. In other words, successful coping means both physiological health and the ability to perform normal behavior. Therefore, the occurrence of normal behavior is viewed as an indicator of welfare in farm animals. Despite the admittance of behavior as an important indicator of animal welfare, there has been a serious dearth of scientific studies on different aspects of animal behavior. This was a serious limitation as a thorough knowledge about the normal behavior of a species is a prerequisite to understand behavior pathologies. This fact was well understood by the formal official movement to ensure animal welfare, the Brambell committee of the United Kingdom. This committee reported that scientific research on animal behavior and related fields is essential to answer many questions that arose over the welfare of captive/farmed animals. The committee report proposed how behavioral research could be used to detect pain and discomfort, understand the cognitive powers of animals, and identify motivations that are thwarted in captivity by the use of preference tests. The committee stimulated
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several animal behavior studies in the United Kingdom and other parts of the world. In addition to the obvious use in animal welfare assessment, knowledge of animal behavior enables human caretakers to solve practical problems of animal housing, management, handling, transport, and health. It also contributes to the science of animal welfare and permits the humans to better use the skills and abilities of animals. Knowing the reasons for abnormal behavior, ethologists can offer ways to prevent or mitigate the problem. Further, behavior principles will help to better design animal accommodations thereby making the environments function better and improve the welfare of animals that live in such facilities. A mere knowledge of the behavior repertoire is not enough to assess the welfare of an animal. It is equally crucial to know whether animal welfare is at risk if the behavior observed differs from that in the natural environment for each species and farming system. This is achieved by animal motivation studies and by studies exploring the effect of environmental structures on animal behavior. In many instances, physiological and/or behavioral responses essential for survival under natural conditions become part of the biology of the species. Such responses persist despite a need for them under domestication. However, from the animal’s perspective, this is a true behavioral response to ensure survival and therefore not being able to perform such a behavior can be a compromise in welfare. An ideal example of such a behavior is altered nest building in periparturient sows despite the need for a nest for piglet survival. Although abnormal behaviors are the common indicators of a compromised welfare, there are positive behavior indicators as well suggestive of good welfare such as cheerful vocalizations and facial expressions in some species. Thus, well being comprises both the absence of negative effects and the presence of positive effects. Motivation and Behavior Behavior is a reflection of the inner state (motivation) of the animal, the brain process behind the overt behavior. Motivation also dictates when behavior is to be exhibited. Motivation studies are thus essential to understand the meaning of the behavior observed. Many altered/abnormal behaviors in animals suggestive of compromised welfare have been linked to motivational problems. Causal factors are the inputs to the decision-making center which are actually the interpretations of different internal and external states of the body like fear or hunger. The motivational state of an animal represents the combination of the levels of all relevant causal factors. Motivation may arise from internal or external source. For example, group-housed sows prefer to eat simultaneously. That means when one sow sees another sow
eating, she also is motivated to eat even if she is not hungry. Here, the source of motivation is external. Similarly, nest building is another behavior expressed by sows prior to farrowing. Even if there is no bedding material in the vicinity, sow will follow the same body movements as if she is building a nest. Here, the motivation is internal. There is no consensus regarding the strength of internal and external motivations. The causal components of a motivational state are difficult to quantify although behavior observation permits us to understand the motivational state of the animal. The motivational state and its strength in animals are studied using preference tests. Preference tests are generally performed in one of the two forms, to identify the motivation or to assess the strength of motivation. In the former, the animal is exposed to two conditions suitable to perform two different behaviors and is permitted to select one depending on its motivational state at that time. In the latter, the animal is given a condition suitable for a particular behavior and required to perform some work to access the condition. Depending on the amount of work performed, the strength of motivation is evaluated.
Behavioral Patterns in Swine The changes in housing and management patterns in swine farming have been rapid with respect to both evolutionary time and the domestication history of the pig. Thus, there is every chance to have problems in meeting the behavioral needs of pigs. This becomes a serious issue given the fact that the behavioral differences between wild pigs and domestic pigs are more quantitative than qualitative in nature.
Social Behavior Pigs in nature live in large social groups. The members within a group exhibit a fixed pattern of relationship between them and with their environment. Social behavior of pigs within a group comprises both agonistic and nonagonistic behaviors. Physical (size, age and sex composition of the group, degree of relationship between members) and social structures of the group as well as group cohesion (length of association between members) have effects on social behavior. Attempts to use the same resource at the same time by more than one individual in the group result in competition which may not necessarily lead to physical conflict. Hierarchy in the social group means that the dominant member is able to restrict the movements of subordinates and their access to resources. The key factor in a social group is communication. Vocal signals are the most important means of communication in pigs. The common vocalizations in pigs are the following.
Pigs: Behavior and Welfare Assessment
. Grunt : lasts for < 1 s and produced in response to familiar voices or during activities such as rooting. . Bark: produced when pigs are startled. . Squeal: intense vocalization produced when aroused. . Scream: vocalization produced by a pig when hurt. Olfactory signals are predominant in recognizing a new member in the group. Experiments using blindfolded pigs have indicated that olfactory stimuli are more important than visual or hearing senses in forming a dominance hierarchy among group members. Although vision plays a less significant role in social behavior, pigs have color vision, a panoramic range of about 310 , and binocular vision of 35–50 . Dominance hierarchy in social groups of pigs
When unfamiliar pigs are mixed together for the first time, they compete with others, characterized by aggressive interactions to establish a dominance hierarchy. Generally, a new hierarchy is established within 24 h of mixing, though the level of aggression drops considerably after 1 h of mixing. The time to establish a hierarchy is longer in older pigs. Once a hierarchy is established, the group may become stable. Hierarchy is not permanent; when a new pig enters or leaves the group, the hierarchy is reorganized. Both sex and body weight are predictors of success in achieving dominance. Female pigs are aggressive for longer duration than castrated males. Although boars are generally dominant over sows, in a group of castrated male pigs and sows, the males may not be dominant. Breed difference in aggression has also been noted, with the Yorkshire more aggressive than Berkshire breed. A breed x sex interaction in the extent of aggressiveness has also been observed, with Hampshire male dominance over females exceeding that of Duroc male pigs. Once a hierarchy is established in a group of pigs, it is maintained by the subordinate pigs in the group avoiding conflicts. Recognition between members in the group and the memory of the social encounters are thus vital factors in maintaining social stability; pigs can recognize and remember 20–30 of their group mates. During the process of hierarchy establishment, dominance is established between each pair of pigs, with aggression usually expressed by the dominant animal. However, once hierarchy is established, the same animal may not appear to be very aggressive, as the relationships are understood by other group members. Following hierarchy formation, overt aggression is replaced by threat (sharp loud grunt and feint with the snout by the dominant pig). Thus, a stable social group of pigs is characterized by a high level of group bonding with a minimal level of aggression. Aggression is an important social behavior in pigs even after the establishment of a social hierarchy since there will be competition for some resources at all times (see section ‘Social Behavior’). The most common aggressive
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behavior is thrusting the head upward or sideways against the head or body of the opponent pig. The fighting pigs strut shoulder to shoulder while attempting to bite each other, usually at the neck, ears, and shoulder region while in a parallel posture. Another common aggressive behavior is levering (snout is put under the body of the opponent from behind). The losing pig in a fight will exhibit the characteristic submissive gesture (twisting the head away from the opponent) and will be usually chased by the winner. The various components of agonistic interactions in pigs, as developed by Jensen and Wood-Gush, are given in Table 1. In many swine-breeding herds, a dynamic grouping system (sows are removed and new sows are added to the group at frequent intervals) is followed to make best use of resources. This results in disruption of the social hierarchy and consequent aggression. When sufficient space is available in such situations, subordinate pigs could inhibit aggression by moving away from the dominant ones. However, if there is physical limitation in performing submissive responses, the aggression remains unresolved and persists at a high level. The problem is exacerbated when resources such as feed are limited. This can be a serious challenge to the welfare of pigs. Similarly, in stall housing systems, the pigs are unable to exhibit submissive behaviors resulting in unresolved aggression. Both the quantity and the quality of space are important as a resource given that in natural surroundings groups of pigs occupy vast areas and forage over long distances daily. Characteristic association between individuals within a group is another feature of social behavior. Certain
Table 1
Agonistic interaction patterns in swine
Agonistic behavior components Inverse parallel pressing Parallel pressing Head-to-body knock Head-to-head knock Nose to nose Nose to body Anal-genital nosing Head tilt Aiming
Retreat
Description Pressing of shoulders against each other, facing opposite directions Pressing of shoulders against each other, facing same direction Hitting with the snout against the body of the receiver Hitting with the snout against the head of the receiver The nose approaches the snout or the head of the receiver The nose approaches the body of the receiver The nose approaches the anogenital area of the receiver The head is lowered and turned away from another animal An upward-directed thrust of the snout, slightly directed at the receiver, from a distance of 2–3 m Takes several steps away from the other animal
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individual members within a group will have closer relationships (affiliation). These pairs evolve by themselves and support each other for their benefit. Strong social relationship between and within sexes and age groups has also been observed. Allogrooming (in pigs – nosing another pig) is another social behavior observed in pigs which is considered to reinforce social bonds within groups and reduce tension between group mates.
Feeding and Drinking Behavior Pigs show characteristic behavior during feeding. Feeding behavior is affected by diurnal rhythms and social factors. Brain inputs such as visual input or input from taste receptors can also influence feeding behavior. Drinking is closely associated with feeding; social factors, diet composition and texture, and environmental temperature strongly influence drinking behavior as well. Social facilitation (tendency for animals to join in an activity) is another factor influencing feeding behavior. Pigs in general prefer to eat simultaneously. This means that a pig fed ad libitum will be motivated eat again if it sees another pig eating. Thus, social facilitation can influence both the frequency of feeding and the quantity consumed. In facilities like the electronic feeding system (ESF), sows are not able to eat simultaneously. This blocks social facilitation and is suggested to cause behavioral and welfare problems. Often, waiting to enter the ESF appears to frustrate the sows, making them aggressive and causing injuries and compromised welfare. The competitive order for feeding is not necessarily linear and varies considerably in different situations. The social hierarchy dictates the feeding order to a great extent, with the dominant sow entering the feeder first. It is also possible that a dominant sow may enter the station repeatedly even after eating their allotted feed, thus restricting the access of submissive sows. Rooting is another important component of feeding behavior in pigs. The snout of the pig is a highly developed sense organ and olfaction plays an important role in feeding behavior. Rooting involves moving the feed material or straw or mud using the snout. Pigs also show distinctive defecation behavior. Pigs prefer to defecate in an area away from the place where they feed or rest.
Nonlocomotory Postural Behaviors Stretching, standing, sitting, lying down, and getting up are some of the nonlocomotory behaviors exhibited by pigs. The definitions of various nonlocomotory behaviors are provided as follows. . Standing : an upright position on extended legs while remaining stationary.
. Sitting : the posture in which most of the body weight and the posterior part of the trunk are in contact and supported by the ground. . Lying : the posture in which the side or ventral part of the body is in contact with the ground. Specific sequences of movements are involved in assuming each posture with a pause of few seconds between phases. Animal needs a certain amount of space for these postures. The first step in preparation for a lying down posture is adopting a stable standing posture. This is followed by the sow dropping down onto the knees and adopting a half-kneeling position. The sow then slides one knee under the body and rests on one knee and one shoulder. This is followed by gradual rotation of the upper part of the body to rest the shoulder and side of the head on the floor. Then, the sow rotates the front half of the body so that the front part becomes almost recumbent on the floor. Subsequently, the sow drops the hind quarters and adopts a sternal or lateral recumbency, in which the ventral surface or the side of the body is supported by the ground, respectively. Similarly, when standing up, the sow first raises up on the front knees to a position similar to sitting, followed by lifting the hind quarters. A sow may lie down vertically (on the belly), laterally (on the side); she may fall down on the side or may lie down by leaning on a wall. The lying down process can thus significantly affect the chances of piglet crushing since most crushing occurs when the sow lies down. . Stretching : Stretching is generally performed after a period of rest or after a period when the limbs are folded. Stretching helps the animal to keep its joints and muscles in a functional state. Sideways, backward, and forward movements are associated with nonlocomotory postural behavioral changes. These impose a dynamic space requirement, which is greater than the static space requirements associated with standing or lying stationary. For instance, while lying down or getting up, the animal makes forward and backward movements. During these postural changes, the animal moves its center of gravity and uses its weight as a counterbalance for rising or as a direct pull when lying down. The movement of center of gravity is achieved by the forward and backward movements of the body and this requires additional space.
Locomotion and Gait Locomotion is an important component of an animal’s activities. Locomotion enables an animal to respond in space and time to meet its different needs. Locomotion disorders have a major impact on the welfare status of animals. In locomotion, limbs act in definite synchronized patterns which are called ‘gaits.’ Gait may be symmetrical
Pigs: Behavior and Welfare Assessment
(limbs on one side repeat those of the other side, but half a stride later) or asymmetrical (limbs from one side do not repeat those of the other). Walk, pace, and trot in horses are symmetrical gaits, whereas canter and gallop in horse are examples of asymmetrical gaits. The full cycle of leg movement during the phases of support, propulsion, and movement of the body through the air is called ‘stride’; stride length is the distance between successive imprints of the same foot. Various aspects of locomotory behavior are important in diagnosing conditions like lameness. For instance, in lame animals, the stride length will be affected. Lame animals will adopt peculiar body movements to adjust the center of gravity. Spacing Behavior There are behavioral parameters associated with space also, which are important especially in social animals such as pigs. Individual space depends on the body dimensions of the animal in a particular posture and individual space moves with the animal. The static area used by an animal refers to its home range and territory. The common terms related to spacing behavior are given as follows. . Flight distance : the radius of space within which the animal will not voluntarily permit the intrusion of man or other animals. The animal may respond by startle, alarm, fight-or-flight display, and vocalizations if the flight distance is violated. . Territory : an area defended by fighting or by demarcation that deters other animals from entering the area. There may not be a permanent territory for an animal. . Individual distance : the minimum distance between an animal and other members in the group; each animal prevents other animals from entering this space. Individual distance includes the physical space (space for its basic movements of lying, rising, standing, stretching, and scratching). The space will be larger in the head region to accommodate the head movements during ingestion, grooming, and gesturing and it includes both vertical and horizontal distances. Individual space protects the animal from body damage due to contact and reduces competition and interference while feeding. Individual distance also provides sufficient space for escape when needed and for separation from diseased animals. Animals have quantitative and qualitative needs in relation to space. The former are related to space occupation, social distance, flight distance, and actual territory, whereas qualitative needs are related to activities such as eating, body care, exploration, kinetics, and social behavior which are space dependent. The quality of space includes the presence of barriers to avoid visual contact with others and concealment locations to avoid aggression from other animals.
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. Social limit : the maximum distance any animal moves away from the group. There is always a balance between individual distance and social limit in stable social groups. The space occupied by an animal is a function of its body weight and its need for various activities. The relationship between space occupied and weight is a constant (‘k’) multiplied by the body weight to the power of 0.67. This constant depends on the extent to which the body shape of the animal deviates from a sphere and the activities that are important for the animal to perform. The values of ‘k’ are different for lateral recumbency and sternal recumbency as the space required differs. Sharing of space occurs when animals are housed in groups since all animals are not performing the same postural behavior at the same time. Generally a ‘k’ value of 0.034 is considered sufficient in group housing systems. Crowding in a group means that the movement of members in the group is restricted by the physical presence of other group members; this increases the chance for violating individual space, which may affect the fitness of the group members especially when resources are limited. Exploratory Behavior Exploration is another important component of swine behavior. Animals are strongly motivated to explore when they are in a new environment. Exploration subsides as the environment becomes familiar and it resumes when there is a change in the environment. Fear associated with novelty is a major reason for exploratory behavior; a novel situation causes the animal some degree of fear. Exploration also helps in preparation for the future such as escape from predator, escape from inclement weather, and ensuring food security. A high degree of awareness is needed to evaluate the situation and to prepare for the future. Given the link between fear and exploration, welfare scientists have suggested that estimating the potential of a new environment or a novel object to induce fear can be used to evaluate the welfare status associated with the housing system. Exploration may be inquisitive (the animal looks for a change) or inspective (the animal responds to a change). The former is considered to be a pleasurable activity for the animal and indicates no immediate needs, whereas the latter represents the behavioral outcome of an interaction between fear and curiosity. In any case, interpretation of this behavior remains the subject of some debate. Sexual Behavior Both sexes of swine exhibit characteristic sexual behaviors. Standing still when pressed on the back (immobility) which is facilitated by the boar odor is a characteristic sign of female sexual behavior in pigs. While in estrus,
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the female pig may become restless at night. Some breeds also show erect ears (ears held stiffly close to the head and turned upward and backward). Female pigs in estrus may also urinate frequently and may produce a soft rhythmic grunt. The female pig will also approach the boar and sniff the boar’s head and genitals. The female pig in estrus will try to mount other estrus females. This behavior eventually transforms into searching behavior for the boar, a behavior that is successfully used to detect estrus in sows using electronic monitoring system. Female pigs are able to identify intact males by the strong boar odor produced by androgen metabolites present in both the saliva and the preputial secretions of boars. Approaching a female pig and nosing her sides, flanks, and vulva is a major sexual behavior in boars. Boars also make a characteristic series (6–8 s 1) of soft guttural grunts (courting song). The boar urinates rhythmically and the pheromones in the urine further stimulate the standing behavior of the female pig. The boar will also foam at the mouth and move its jaw from side to side. Boars do not exhibit flehmen (lip curling; turning up of the upper lip in response to an odor). Instead, boars gape when they encounter sow urine. The major sexual arousing factor in boar is suggested to be the female pig’s willingness to stand still and not the olfactory signals. Prepartum Behaviors During the preparturient period (ranging from late gestation to the beginning of the first stage of labor), sows exhibit different behaviors when in the natural surroundings. However, not all of them may be visible in the confined systems. Nest building (gathering nest materials such as grass or sticks and arranging it by rooting and nosing), which starts between 3 days and 24 h before farrowing, is the most notable prepartum behavior. The duration of nest building may vary among sows. During nest building, the sow uses her forelimbs to move the bedding, known as ‘pawing.’ Sows may show nest-building behavior even if there are no materials available to them. Sows will stop all these activities as time advances and adopt a lateral recumbency before farrowing. This is followed by a period of restlessness and frequent change of position. The frequency of postural changes increases before the sow adopts a final lying posture. Piglets are farrowed every 15–30 min and the sow will remain in lateral recumbency until farrowing is completed. Sows remain mostly inactive during the first 48 h after farrowing which helps to minimize piglet crushing and to facilitate establishment of a teat order. Postpartum Behavior Postpartum behavior by the sow forms part of the strategy to protect the piglets. Like bovines, sows also eat placenta
(placentophagia) which may help to recycle nutrients and to minimize chances of predation by removing odors. Sows generally do not lick or groom their piglets, but may nose the piglets. The sow also produces repeated short grunts to invite the piglets to feed on colostrum. She appears very nervous at this time and is easily disturbed by the presence of an intruder; this may lead to movements by the sow causing piglet crushing. Sows are very defensive of the piglets and may attack with barks and open mouth if approached. Piglets will stand on their feet within minutes after birth and will start searching for a teat, facilitated by the grunts of the sow. The firstborn piglet uses thermal, tactile, and olfactory cues to locate the teat and may be slow to find teat. However, subsequent piglets respond to the voices of their littermates and quickly locate the udder. The sow will remain stationary in lateral recumbency and may change position to help the piglet locate a teat. Sensory inputs such as vocalization, odors from mammary and birth fluids, and hair patterns of the sow are suggested to help the piglets to locate the teat. Colostrum is available continuously for the first few hours; 10 h after farrowing, milk let down becomes synchronized and periodic. Letting down occurs once in every 50–60 min and each letting down lasts for 10–25 s. The piglets learn the sow’s call and will be ready at the teat for milk. The interval between letting down is longer at night than during the day. Sows generally do not respond to feel or sight of a piglet under them though they respond to loud squeals. Sows are reported to be most responsive to piglet squeals on the first 2 days postpartum. New-Born Piglet Behavior The most import aspect of neonatal behavior is the huddling together of piglets to conserve heat since their thermoregulatory mechanism is poorly developed. The first stage in the suckling process is marked by the vigorous, rhythmic up-and-down movements around one segment of udder by the piglet using its snout for about a minute. This is followed by slow suckling with the tongue wrapped around the teat for about 20 s. Then, the slow suckling is followed by rapid mouth movements as milk starts to flow for about 10–20 s. During this phase, the piglets’ ears are flattened, and their head moves along with suckling movements. After 10–20 s of milk flow, the piglets may show slow mouth movement or move to another teat for more milk. After nursing, the piglets leave the udder or fall asleep in position. The sow stops rhythmic grunts once the piglets stop suckling. Piglets establish a teat order within the first day of their life and will return to the same teat during the entire lactation. Piglets compete for the most productive teat regardless of its position in the udder. Piglets show their
Pigs: Behavior and Welfare Assessment
characteristic defecation behavior within 4 days of birth. Piglets sleep on average 10.5 h day 1 during the first 5 weeks. In nature, sows and their piglets stay together for several weeks. Piglets start showing play behavior (tossing and waving the head, spinning around) when they are 2-days old and will reach a peak between 2 and 6 weeks of age. The play behavior facilitates socialization with group members. Abnormal Behavior Abnormal behaviors are generally considered indicators of compromised welfare in animals. Abnormal behavior is defined as a clear deviation from the normal behavior expressed by majority of the members of the species when they are allowed to perform their full range of behaviors. Abnormal behavior may be harmful to animal itself and/or to other members in the group. Provision of manipulable substances and thereby avoiding barren environments will help reduce most of the abnormal behaviors. Common abnormal behaviors in pigs are described as follows. Stereotypy
Stereotypy is a repetition of sequence of movements without any apparent reason. The repetition may be regular or irregular and may be short or long. Stereotypies are linked to the dopamine release systems in the brain that control body movements. Stereotypies are generally exhibited when the animal has no control over its environment, causing frustration. The argument that stereotypy is part of an animal’s coping mechanism has not been widely accepted. Even if it is so, the indication is that welfare is compromised. Sham chewing (pig imitates chewing movements even when there is no food to chew, characterized by chewing, mouth gaping, and frothing and foaming of saliva), bar biting (animal opens and closes its mouth around a bar/metal piping of the stall, engaging the tongue and teeth with surface and performing chewing movements) are common stereotypies noticed in pigs especially in stall-housed pigs. Continuous repeated pressing of the drinker by some sows is also considered to be a stereotypy. Provision of straw or other manipulable material has shown to reduce most of the stereotypic behaviors. Tail biting
Tail biting is an abnormal behavior that occurs mainly in grow-finish pigs and that is directed to group mates. Crowding and consequent inadequacy of feeder and waterer spaces in group housing is associated with tail biting. Environmental factors such as high temperature, humidity, and noise may exacerbate the situation. However, lack of oral stimulation is suggested to be the major reason for this abnormal behavior. The incidence of tail biting is increased among pigs housed without bedding on
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slatted floors and ones that are fed automatically. Hunger also predisposes pigs to tail biting. The bleeding from tail biting stimulates further tail biting. Provision of rooting materials has been shown to reduce tail biting. Docking may reduce tail biting though it may lead to another abnormal behavior, ear chewing. Vulva biting
This is very common in ESF systems where the hungry sows are forced to wait to access the feeder. As in tail biting, the bleeding from the wound stimulates further biting. Anal massage
Anal massage is an abnormal behavior noticed in growing pigs, especially in docked pigs. Providing objects to chew and root will help to minimize this problem. Belly nosing
It is the up-and-down movement of the snout and the top of the nose on the belly of other pigs, on the soft tissue between their hind legs and between their forelegs. This is common in early weaned piglets, especially those that continue to show teat-seeking behavior, which gets directed toward other piglets. Cannibalism
This is an abnormal behavior mostly seen in sows with first litters where the sow may kill and eat her own piglets. In its mildest form, the hyper-reactive sow may accidentally crush and kill the piglets which are then eaten partially or fully. In severe forms, the sow tries actively to avoid piglets and approaching piglets are attacked, killed, and eaten fully or partially. Once started, cannibalism usually stops only after the death of the entire litter. Cannibalism is associated with hyperexcitability of the sow following farrowing, due to the novelty of the farrowing environment. Providing bedding before farrowing and allowing sows to build nests may reduce cannibalism. Pigs are highly motivated to explore their environment and spend 75% of their active time in foraging-related behavior. Provision of concentrates in a single location as in confined systems requires the animal to satisfy all its food intake needs within a short time, while not satisfying the motivation to explore and forage. In the barren environment, these behavioral needs are redirected at unsuitable targets such as pen mates. Lack of substrates is the major reason for abnormal behaviors such as tail biting and ear chewing. Studies have suggested that even the modern swine breeds retain the behavioral features of wild boars. Most of these natural behaviors are controlled by internal factors, and therefore swine welfare is compromised by a lack of opportunities to perform the behaviors that they are strongly motivated to perform.
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Sickness Behavior Sickness behavior is defined as the expression of the adaptive reorganization of the priorities of the host during an infectious period. The major feature of sickness behavior is a general decrease in activity (immobility, sleepiness, reduced food and water intake). Sickness behavior may be interrupted in response to important strong stimuli (e.g., a sick sow may respond to a newborn piglet). The reduction in activity helps the animal conserve energy, and spend more time resting and sleeping. However, reduction in activity may not occur in all cases. A sick animal will try to move away from its group. This helps the animal to be away from the disturbances of its group mates and minimizes the chances of transmission of disease. It is argued that the behaviors shown by sick animals are part of a strategy to fight disease. Behaviors such as play, grooming, sexual behavior will be reduced in illness, as animals divert resources for maintaining body temperature and combating pathogens.
Using Behavioral Principles to Improve Pig Welfare Pigs prefer to live in large static groups with plenty of space and opportunities to perform many of their natural motivations. However, it is a practical and economic challenge to offer these facilities under commercial farming. For instance, space is a limiting factor in farms. Similarly, dynamic grouping with frequent mixing of pigs may be required to ensure better facility use. However, a knowledge of swine behavior can be successfully utilized to mitigate the threats to the welfare of domestic swine. Aggression is unavoidable when unfamiliar pigs are mixed together. However, the extent of aggression is determined by the method of feeding, and the amount and quality of space. Similarly, aggression at mixing can be influenced by design of the system and by management techniques. For instance, allowing small subgroup formation has been indicated to reduce aggression at mixing. The shape of the pen is also important in determining the level of aggression, with higher aggression in circular pens, and lower aggression in pens with a solid barrier. Aggressive interactions can be reduced over the short term by mixing pigs after sunset, administering some pharmacologic compounds, and the presence of boar at the time of mixing. Space availability is another issue as pigs in groups require space to show submissive behavior (e.g., running away). Providing the space necessary to perform this behavior will ensure quick establishment of social hierarchy and stability in the group. It has been suggested that the psychological stress associated with nonresolvable aggressive interactions among stall-housed sows is a chronic stressor.
Unique Problems in Assessing Welfare by Behavior Obviously, welfare is a multifactorial concept. Therefore, behavior alone cannot be an adequate indicator of welfare in animals. However, given that behavior change is the first overt and perhaps the major indicator of compromised welfare, we are justified in using it in animal welfare assessment. At the same time, it is important to remember that we as humans are ascribing meanings to the behaviors of another species, and to that extent our interpretations can be erroneous. Often, behavioral pathologies are used as indicators of compromised welfare. However, it is important to understand the positive behaviors in animals and their link to welfare. Many times, stress physiology is used to assess the existence of a positive state or at least the absence of a negative emotional state in animals. However, physiological parameters such as heart rate, respiration rate, and cortisol levels are influenced by factors not adversely affecting the welfare of the animals. For instance, sexual excitement can increase the heart rate and respiration rate without any adverse effect on the welfare of the animals. Individual differences, developmental changes, and diurnal variations in measures can also affect the interpretation of the final result. Thus, subjective assessment is also frequently needed for successful welfare assessment. Nonetheless, the extent to which a human observer can accurately assess the mental feeling of the animal is debatable. This is a serious limitation in using behavioral indicators for welfare assessment. Motivational studies evaluating the animal’s ‘willingness to work’ have been suggested as useful in assessing the state of the animal. Even then the correct interpretation demands appropriate experimental designs and sophisticated operant equipment. Even though preference tests are used in housing system studies, they are not perfect. The main limitation is that the results are unique to the testing situation. The behavioral choice of the animal may vary with the duration of exposure. Above all, it may be difficult to establish a scientific rationale for the choices made by the animal because those choices may not always be the best for the subject. The multifactorial nature of animal welfare also raises the issue of how to weight those factors. Often, a higher importance is given to factors which humans value had they been exposed to such a welfare threat. It is also possible that different indicators may provide conflicting interpretations. For instance, physiological and behavioral indicators provide different assessment of the pain associated with castration. Similarly, behavioral and health indicators have come up with different conclusions regarding the welfare implications of providing bedding for pigs. Another difficult issue, even when positive behaviors are used to assess the welfare status, is the level of such
Pigs: Behavior and Welfare Assessment
behaviors. For example, allogrooming is generally considered as a positive behavior in social groups of pigs. Nevertheless, excessive levels of allogrooming activity may not necessarily reflect positive states of the animal as they are likely to disturb the receiver. Obviously, there are no objective indicators to assess this and no gold standard has been established. Similarly, the ability of the animal to perform various postural behaviors is critical with respect to its welfare. But there are no scientifically valid numbers available regarding the duration or frequency of postural behaviors, leaving the assessor to resort to subjective judgments.
Areas Where More Research Is Needed Obviously, all the limitations mentioned earlier warrant further research. However, there are promising areas that are expected to advance human knowledge about animal behavior. These have the potential to improve the welfare of domestic animals. One little-researched area is sickness
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behavior and its value as a disease indicator. Similarly, studies are needed to understand how to assess the positive experiences in animals that are suggested to be important components of good welfare. This issue is crucial because well being is not merely the absence of negative effects, but instead, predominantly the presence of positive effects. Affiliation (closer relationship between certain pairs of individuals) is a type of social behavior exhibited by many farm animal species. Affiliative behavior has been suggested to create a ‘positive mood’ in animals. However, the number of studies focusing on this behavior is considerably less than those involving social competition. Our efforts to focus on negative behaviors will only enable us to help the animal meet its needs and thereby avoid suffering. Research is also needed to understand how to use positive experiences to a better quality of life to the animals and to improve their health. See also: Beyond Fever: Comparative Perspectives on Sickness Behavior; Self-Medication: Passive Prevention and Active Treatment; Welfare of Animals: Introduction.
Current Uses of Behavior to Determine Welfare Status Introduction The welfare of farmed animals has received increased attention in the recent times. Compromised welfare leads to reduction in productivity. Additionally, market forces can be negative when the welfare is shown to be poor. Thus, compromised animal welfare affects the economic sustainability of animal agriculture in more than one way. However, from the producers’ perspective, there is considerable difficulty in demonstrating that adequate welfare has been ensured. The major reason for this is the lack of objective and scientific tools to evaluate animal welfare. Without objective quantification, a compromise in welfare cannot be approved nor can the efficacy of corrective measures assessed. Animal welfare involves several factors, many of which are influenced by factors other than threats to welfare. Nevertheless, behavioral changes are the first and obvious indicators of compromised welfare in animals, though the identification of the same requires thorough knowledge about the normal behavior of the species concerned. The aim of this article is to explain the importance of behavior in swine welfare assessment. Importance of Behavior in Animal Welfare Assessment Animal welfare is a multidisciplinary concept. Behavioral, physiological, and hormonal indicators are employed to assess the welfare of animals. Among these disciplines, the study of animal behavior is an important component. A major reason for the prominence of behavior as a tool in welfare assessment is that changes in behavior patterns are among the most rapid and visible responses of an animal to changes in its environment. Behavior is the way in which the animal expresses its basic needs, deficits, and happiness in an environment. The study of behavior (ethology) involves not only what an animal does but also when, how, why, and where the behavior occurred. Understanding animal behavior is the best way to know whether we are keeping the animals appropriately. The behavior of an animal is influenced by both the structure and function of the animal as well as by the interaction of the animal with the external environment. All categories of pigs under farm conditions are exposed to different types of challenges to their welfare. These challenges vary depending on different aspects of
farming such as routine management, housing, slaughter, and transport. The major welfare concern associated with housing is close confinement in barren environments. The significance of animal welfare is associated with an animal’s adaptive response to stress and its impact on biological functioning. The first response to stress is an alteration in behavior in order to cope with the stressful environment. This may or may not be accompanied by changes in physiological parameters such as respiration and/or heart rate to support the coping efforts. In many instances, it is possible to objectively assess the changes in physiological responses. However, the difficulty is in using the physiological changes alone to identify or quantify the compromise in welfare as many of the physiological parameters are influenced by factors not necessarily threats to the welfare. Therefore, a system evaluation, using a multidisciplinary approach, has been suggested to be the ideal way to assess animal welfare. By nature, each species has its own unique behavioral repertoire (the ethogram) to cope with problems in its natural environment. Scientific studies in farm animals under seminatural conditions have indicated only meager changes in their behavioral repertoire despite domestication. This is the major reason for the widespread consensus that animals should be able perform their natural behavior in order for their welfare to be at a high level. Thus, animal welfare is often defined in terms of natural living or normal functioning of behavioral systems. In other words, successful coping means both physiological health and the ability to perform normal behavior. Therefore, the occurrence of normal behavior is viewed as an indicator of welfare in farm animals. Despite the admittance of behavior as an important indicator of animal welfare, there has been a serious dearth of scientific studies on different aspects of animal behavior. This was a serious limitation as a thorough knowledge about the normal behavior of a species is a prerequisite to understand behavior pathologies. This fact was well understood by the formal official movement to ensure animal welfare, the Brambell committee of the United Kingdom. This committee reported that scientific research on animal behavior and related fields is essential to answer many questions that arose over the welfare of captive/farmed animals. The committee report proposed how behavioral research could be used to detect pain and discomfort, understand the cognitive powers of animals, and identify motivations that are thwarted in captivity by the use of preference tests. The committee stimulated
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several animal behavior studies in the United Kingdom and other parts of the world. In addition to the obvious use in animal welfare assessment, knowledge of animal behavior enables human caretakers to solve practical problems of animal housing, management, handling, transport, and health. It also contributes to the science of animal welfare and permits the humans to better use the skills and abilities of animals. Knowing the reasons for abnormal behavior, ethologists can offer ways to prevent or mitigate the problem. Further, behavior principles will help to better design animal accommodations thereby making the environments function better and improve the welfare of animals that live in such facilities. A mere knowledge of the behavior repertoire is not enough to assess the welfare of an animal. It is equally crucial to know whether animal welfare is at risk if the behavior observed differs from that in the natural environment for each species and farming system. This is achieved by animal motivation studies and by studies exploring the effect of environmental structures on animal behavior. In many instances, physiological and/or behavioral responses essential for survival under natural conditions become part of the biology of the species. Such responses persist despite a need for them under domestication. However, from the animal’s perspective, this is a true behavioral response to ensure survival and therefore not being able to perform such a behavior can be a compromise in welfare. An ideal example of such a behavior is altered nest building in periparturient sows despite the need for a nest for piglet survival. Although abnormal behaviors are the common indicators of a compromised welfare, there are positive behavior indicators as well suggestive of good welfare such as cheerful vocalizations and facial expressions in some species. Thus, well being comprises both the absence of negative effects and the presence of positive effects. Motivation and Behavior Behavior is a reflection of the inner state (motivation) of the animal, the brain process behind the overt behavior. Motivation also dictates when behavior is to be exhibited. Motivation studies are thus essential to understand the meaning of the behavior observed. Many altered/abnormal behaviors in animals suggestive of compromised welfare have been linked to motivational problems. Causal factors are the inputs to the decision-making center which are actually the interpretations of different internal and external states of the body like fear or hunger. The motivational state of an animal represents the combination of the levels of all relevant causal factors. Motivation may arise from internal or external source. For example, group-housed sows prefer to eat simultaneously. That means when one sow sees another sow
eating, she also is motivated to eat even if she is not hungry. Here, the source of motivation is external. Similarly, nest building is another behavior expressed by sows prior to farrowing. Even if there is no bedding material in the vicinity, sow will follow the same body movements as if she is building a nest. Here, the motivation is internal. There is no consensus regarding the strength of internal and external motivations. The causal components of a motivational state are difficult to quantify although behavior observation permits us to understand the motivational state of the animal. The motivational state and its strength in animals are studied using preference tests. Preference tests are generally performed in one of the two forms, to identify the motivation or to assess the strength of motivation. In the former, the animal is exposed to two conditions suitable to perform two different behaviors and is permitted to select one depending on its motivational state at that time. In the latter, the animal is given a condition suitable for a particular behavior and required to perform some work to access the condition. Depending on the amount of work performed, the strength of motivation is evaluated.
Behavioral Patterns in Swine The changes in housing and management patterns in swine farming have been rapid with respect to both evolutionary time and the domestication history of the pig. Thus, there is every chance to have problems in meeting the behavioral needs of pigs. This becomes a serious issue given the fact that the behavioral differences between wild pigs and domestic pigs are more quantitative than qualitative in nature.
Social Behavior Pigs in nature live in large social groups. The members within a group exhibit a fixed pattern of relationship between them and with their environment. Social behavior of pigs within a group comprises both agonistic and nonagonistic behaviors. Physical (size, age and sex composition of the group, degree of relationship between members) and social structures of the group as well as group cohesion (length of association between members) have effects on social behavior. Attempts to use the same resource at the same time by more than one individual in the group result in competition which may not necessarily lead to physical conflict. Hierarchy in the social group means that the dominant member is able to restrict the movements of subordinates and their access to resources. The key factor in a social group is communication. Vocal signals are the most important means of communication in pigs. The common vocalizations in pigs are the following.
Pigs: Behavior and Welfare Assessment
. Grunt : lasts for < 1 s and produced in response to familiar voices or during activities such as rooting. . Bark: produced when pigs are startled. . Squeal: intense vocalization produced when aroused. . Scream: vocalization produced by a pig when hurt. Olfactory signals are predominant in recognizing a new member in the group. Experiments using blindfolded pigs have indicated that olfactory stimuli are more important than visual or hearing senses in forming a dominance hierarchy among group members. Although vision plays a less significant role in social behavior, pigs have color vision, a panoramic range of about 310 , and binocular vision of 35–50 . Dominance hierarchy in social groups of pigs
When unfamiliar pigs are mixed together for the first time, they compete with others, characterized by aggressive interactions to establish a dominance hierarchy. Generally, a new hierarchy is established within 24 h of mixing, though the level of aggression drops considerably after 1 h of mixing. The time to establish a hierarchy is longer in older pigs. Once a hierarchy is established, the group may become stable. Hierarchy is not permanent; when a new pig enters or leaves the group, the hierarchy is reorganized. Both sex and body weight are predictors of success in achieving dominance. Female pigs are aggressive for longer duration than castrated males. Although boars are generally dominant over sows, in a group of castrated male pigs and sows, the males may not be dominant. Breed difference in aggression has also been noted, with the Yorkshire more aggressive than Berkshire breed. A breed x sex interaction in the extent of aggressiveness has also been observed, with Hampshire male dominance over females exceeding that of Duroc male pigs. Once a hierarchy is established in a group of pigs, it is maintained by the subordinate pigs in the group avoiding conflicts. Recognition between members in the group and the memory of the social encounters are thus vital factors in maintaining social stability; pigs can recognize and remember 20–30 of their group mates. During the process of hierarchy establishment, dominance is established between each pair of pigs, with aggression usually expressed by the dominant animal. However, once hierarchy is established, the same animal may not appear to be very aggressive, as the relationships are understood by other group members. Following hierarchy formation, overt aggression is replaced by threat (sharp loud grunt and feint with the snout by the dominant pig). Thus, a stable social group of pigs is characterized by a high level of group bonding with a minimal level of aggression. Aggression is an important social behavior in pigs even after the establishment of a social hierarchy since there will be competition for some resources at all times (see section ‘Social Behavior’). The most common aggressive
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behavior is thrusting the head upward or sideways against the head or body of the opponent pig. The fighting pigs strut shoulder to shoulder while attempting to bite each other, usually at the neck, ears, and shoulder region while in a parallel posture. Another common aggressive behavior is levering (snout is put under the body of the opponent from behind). The losing pig in a fight will exhibit the characteristic submissive gesture (twisting the head away from the opponent) and will be usually chased by the winner. The various components of agonistic interactions in pigs, as developed by Jensen and Wood-Gush, are given in Table 1. In many swine-breeding herds, a dynamic grouping system (sows are removed and new sows are added to the group at frequent intervals) is followed to make best use of resources. This results in disruption of the social hierarchy and consequent aggression. When sufficient space is available in such situations, subordinate pigs could inhibit aggression by moving away from the dominant ones. However, if there is physical limitation in performing submissive responses, the aggression remains unresolved and persists at a high level. The problem is exacerbated when resources such as feed are limited. This can be a serious challenge to the welfare of pigs. Similarly, in stall housing systems, the pigs are unable to exhibit submissive behaviors resulting in unresolved aggression. Both the quantity and the quality of space are important as a resource given that in natural surroundings groups of pigs occupy vast areas and forage over long distances daily. Characteristic association between individuals within a group is another feature of social behavior. Certain
Table 1
Agonistic interaction patterns in swine
Agonistic behavior components Inverse parallel pressing Parallel pressing Head-to-body knock Head-to-head knock Nose to nose Nose to body Anal-genital nosing Head tilt Aiming
Retreat
Description Pressing of shoulders against each other, facing opposite directions Pressing of shoulders against each other, facing same direction Hitting with the snout against the body of the receiver Hitting with the snout against the head of the receiver The nose approaches the snout or the head of the receiver The nose approaches the body of the receiver The nose approaches the anogenital area of the receiver The head is lowered and turned away from another animal An upward-directed thrust of the snout, slightly directed at the receiver, from a distance of 2–3 m Takes several steps away from the other animal
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individual members within a group will have closer relationships (affiliation). These pairs evolve by themselves and support each other for their benefit. Strong social relationship between and within sexes and age groups has also been observed. Allogrooming (in pigs – nosing another pig) is another social behavior observed in pigs which is considered to reinforce social bonds within groups and reduce tension between group mates.
Feeding and Drinking Behavior Pigs show characteristic behavior during feeding. Feeding behavior is affected by diurnal rhythms and social factors. Brain inputs such as visual input or input from taste receptors can also influence feeding behavior. Drinking is closely associated with feeding; social factors, diet composition and texture, and environmental temperature strongly influence drinking behavior as well. Social facilitation (tendency for animals to join in an activity) is another factor influencing feeding behavior. Pigs in general prefer to eat simultaneously. This means that a pig fed ad libitum will be motivated eat again if it sees another pig eating. Thus, social facilitation can influence both the frequency of feeding and the quantity consumed. In facilities like the electronic feeding system (ESF), sows are not able to eat simultaneously. This blocks social facilitation and is suggested to cause behavioral and welfare problems. Often, waiting to enter the ESF appears to frustrate the sows, making them aggressive and causing injuries and compromised welfare. The competitive order for feeding is not necessarily linear and varies considerably in different situations. The social hierarchy dictates the feeding order to a great extent, with the dominant sow entering the feeder first. It is also possible that a dominant sow may enter the station repeatedly even after eating their allotted feed, thus restricting the access of submissive sows. Rooting is another important component of feeding behavior in pigs. The snout of the pig is a highly developed sense organ and olfaction plays an important role in feeding behavior. Rooting involves moving the feed material or straw or mud using the snout. Pigs also show distinctive defecation behavior. Pigs prefer to defecate in an area away from the place where they feed or rest.
Nonlocomotory Postural Behaviors Stretching, standing, sitting, lying down, and getting up are some of the nonlocomotory behaviors exhibited by pigs. The definitions of various nonlocomotory behaviors are provided as follows. . Standing : an upright position on extended legs while remaining stationary.
. Sitting : the posture in which most of the body weight and the posterior part of the trunk are in contact and supported by the ground. . Lying : the posture in which the side or ventral part of the body is in contact with the ground. Specific sequences of movements are involved in assuming each posture with a pause of few seconds between phases. Animal needs a certain amount of space for these postures. The first step in preparation for a lying down posture is adopting a stable standing posture. This is followed by the sow dropping down onto the knees and adopting a half-kneeling position. The sow then slides one knee under the body and rests on one knee and one shoulder. This is followed by gradual rotation of the upper part of the body to rest the shoulder and side of the head on the floor. Then, the sow rotates the front half of the body so that the front part becomes almost recumbent on the floor. Subsequently, the sow drops the hind quarters and adopts a sternal or lateral recumbency, in which the ventral surface or the side of the body is supported by the ground, respectively. Similarly, when standing up, the sow first raises up on the front knees to a position similar to sitting, followed by lifting the hind quarters. A sow may lie down vertically (on the belly), laterally (on the side); she may fall down on the side or may lie down by leaning on a wall. The lying down process can thus significantly affect the chances of piglet crushing since most crushing occurs when the sow lies down. . Stretching : Stretching is generally performed after a period of rest or after a period when the limbs are folded. Stretching helps the animal to keep its joints and muscles in a functional state. Sideways, backward, and forward movements are associated with nonlocomotory postural behavioral changes. These impose a dynamic space requirement, which is greater than the static space requirements associated with standing or lying stationary. For instance, while lying down or getting up, the animal makes forward and backward movements. During these postural changes, the animal moves its center of gravity and uses its weight as a counterbalance for rising or as a direct pull when lying down. The movement of center of gravity is achieved by the forward and backward movements of the body and this requires additional space.
Locomotion and Gait Locomotion is an important component of an animal’s activities. Locomotion enables an animal to respond in space and time to meet its different needs. Locomotion disorders have a major impact on the welfare status of animals. In locomotion, limbs act in definite synchronized patterns which are called ‘gaits.’ Gait may be symmetrical
Pigs: Behavior and Welfare Assessment
(limbs on one side repeat those of the other side, but half a stride later) or asymmetrical (limbs from one side do not repeat those of the other). Walk, pace, and trot in horses are symmetrical gaits, whereas canter and gallop in horse are examples of asymmetrical gaits. The full cycle of leg movement during the phases of support, propulsion, and movement of the body through the air is called ‘stride’; stride length is the distance between successive imprints of the same foot. Various aspects of locomotory behavior are important in diagnosing conditions like lameness. For instance, in lame animals, the stride length will be affected. Lame animals will adopt peculiar body movements to adjust the center of gravity. Spacing Behavior There are behavioral parameters associated with space also, which are important especially in social animals such as pigs. Individual space depends on the body dimensions of the animal in a particular posture and individual space moves with the animal. The static area used by an animal refers to its home range and territory. The common terms related to spacing behavior are given as follows. . Flight distance : the radius of space within which the animal will not voluntarily permit the intrusion of man or other animals. The animal may respond by startle, alarm, fight-or-flight display, and vocalizations if the flight distance is violated. . Territory : an area defended by fighting or by demarcation that deters other animals from entering the area. There may not be a permanent territory for an animal. . Individual distance : the minimum distance between an animal and other members in the group; each animal prevents other animals from entering this space. Individual distance includes the physical space (space for its basic movements of lying, rising, standing, stretching, and scratching). The space will be larger in the head region to accommodate the head movements during ingestion, grooming, and gesturing and it includes both vertical and horizontal distances. Individual space protects the animal from body damage due to contact and reduces competition and interference while feeding. Individual distance also provides sufficient space for escape when needed and for separation from diseased animals. Animals have quantitative and qualitative needs in relation to space. The former are related to space occupation, social distance, flight distance, and actual territory, whereas qualitative needs are related to activities such as eating, body care, exploration, kinetics, and social behavior which are space dependent. The quality of space includes the presence of barriers to avoid visual contact with others and concealment locations to avoid aggression from other animals.
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. Social limit : the maximum distance any animal moves away from the group. There is always a balance between individual distance and social limit in stable social groups. The space occupied by an animal is a function of its body weight and its need for various activities. The relationship between space occupied and weight is a constant (‘k’) multiplied by the body weight to the power of 0.67. This constant depends on the extent to which the body shape of the animal deviates from a sphere and the activities that are important for the animal to perform. The values of ‘k’ are different for lateral recumbency and sternal recumbency as the space required differs. Sharing of space occurs when animals are housed in groups since all animals are not performing the same postural behavior at the same time. Generally a ‘k’ value of 0.034 is considered sufficient in group housing systems. Crowding in a group means that the movement of members in the group is restricted by the physical presence of other group members; this increases the chance for violating individual space, which may affect the fitness of the group members especially when resources are limited. Exploratory Behavior Exploration is another important component of swine behavior. Animals are strongly motivated to explore when they are in a new environment. Exploration subsides as the environment becomes familiar and it resumes when there is a change in the environment. Fear associated with novelty is a major reason for exploratory behavior; a novel situation causes the animal some degree of fear. Exploration also helps in preparation for the future such as escape from predator, escape from inclement weather, and ensuring food security. A high degree of awareness is needed to evaluate the situation and to prepare for the future. Given the link between fear and exploration, welfare scientists have suggested that estimating the potential of a new environment or a novel object to induce fear can be used to evaluate the welfare status associated with the housing system. Exploration may be inquisitive (the animal looks for a change) or inspective (the animal responds to a change). The former is considered to be a pleasurable activity for the animal and indicates no immediate needs, whereas the latter represents the behavioral outcome of an interaction between fear and curiosity. In any case, interpretation of this behavior remains the subject of some debate. Sexual Behavior Both sexes of swine exhibit characteristic sexual behaviors. Standing still when pressed on the back (immobility) which is facilitated by the boar odor is a characteristic sign of female sexual behavior in pigs. While in estrus,
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the female pig may become restless at night. Some breeds also show erect ears (ears held stiffly close to the head and turned upward and backward). Female pigs in estrus may also urinate frequently and may produce a soft rhythmic grunt. The female pig will also approach the boar and sniff the boar’s head and genitals. The female pig in estrus will try to mount other estrus females. This behavior eventually transforms into searching behavior for the boar, a behavior that is successfully used to detect estrus in sows using electronic monitoring system. Female pigs are able to identify intact males by the strong boar odor produced by androgen metabolites present in both the saliva and the preputial secretions of boars. Approaching a female pig and nosing her sides, flanks, and vulva is a major sexual behavior in boars. Boars also make a characteristic series (6–8 s 1) of soft guttural grunts (courting song). The boar urinates rhythmically and the pheromones in the urine further stimulate the standing behavior of the female pig. The boar will also foam at the mouth and move its jaw from side to side. Boars do not exhibit flehmen (lip curling; turning up of the upper lip in response to an odor). Instead, boars gape when they encounter sow urine. The major sexual arousing factor in boar is suggested to be the female pig’s willingness to stand still and not the olfactory signals. Prepartum Behaviors During the preparturient period (ranging from late gestation to the beginning of the first stage of labor), sows exhibit different behaviors when in the natural surroundings. However, not all of them may be visible in the confined systems. Nest building (gathering nest materials such as grass or sticks and arranging it by rooting and nosing), which starts between 3 days and 24 h before farrowing, is the most notable prepartum behavior. The duration of nest building may vary among sows. During nest building, the sow uses her forelimbs to move the bedding, known as ‘pawing.’ Sows may show nest-building behavior even if there are no materials available to them. Sows will stop all these activities as time advances and adopt a lateral recumbency before farrowing. This is followed by a period of restlessness and frequent change of position. The frequency of postural changes increases before the sow adopts a final lying posture. Piglets are farrowed every 15–30 min and the sow will remain in lateral recumbency until farrowing is completed. Sows remain mostly inactive during the first 48 h after farrowing which helps to minimize piglet crushing and to facilitate establishment of a teat order. Postpartum Behavior Postpartum behavior by the sow forms part of the strategy to protect the piglets. Like bovines, sows also eat placenta
(placentophagia) which may help to recycle nutrients and to minimize chances of predation by removing odors. Sows generally do not lick or groom their piglets, but may nose the piglets. The sow also produces repeated short grunts to invite the piglets to feed on colostrum. She appears very nervous at this time and is easily disturbed by the presence of an intruder; this may lead to movements by the sow causing piglet crushing. Sows are very defensive of the piglets and may attack with barks and open mouth if approached. Piglets will stand on their feet within minutes after birth and will start searching for a teat, facilitated by the grunts of the sow. The firstborn piglet uses thermal, tactile, and olfactory cues to locate the teat and may be slow to find teat. However, subsequent piglets respond to the voices of their littermates and quickly locate the udder. The sow will remain stationary in lateral recumbency and may change position to help the piglet locate a teat. Sensory inputs such as vocalization, odors from mammary and birth fluids, and hair patterns of the sow are suggested to help the piglets to locate the teat. Colostrum is available continuously for the first few hours; 10 h after farrowing, milk let down becomes synchronized and periodic. Letting down occurs once in every 50–60 min and each letting down lasts for 10–25 s. The piglets learn the sow’s call and will be ready at the teat for milk. The interval between letting down is longer at night than during the day. Sows generally do not respond to feel or sight of a piglet under them though they respond to loud squeals. Sows are reported to be most responsive to piglet squeals on the first 2 days postpartum. New-Born Piglet Behavior The most import aspect of neonatal behavior is the huddling together of piglets to conserve heat since their thermoregulatory mechanism is poorly developed. The first stage in the suckling process is marked by the vigorous, rhythmic up-and-down movements around one segment of udder by the piglet using its snout for about a minute. This is followed by slow suckling with the tongue wrapped around the teat for about 20 s. Then, the slow suckling is followed by rapid mouth movements as milk starts to flow for about 10–20 s. During this phase, the piglets’ ears are flattened, and their head moves along with suckling movements. After 10–20 s of milk flow, the piglets may show slow mouth movement or move to another teat for more milk. After nursing, the piglets leave the udder or fall asleep in position. The sow stops rhythmic grunts once the piglets stop suckling. Piglets establish a teat order within the first day of their life and will return to the same teat during the entire lactation. Piglets compete for the most productive teat regardless of its position in the udder. Piglets show their
Pigs: Behavior and Welfare Assessment
characteristic defecation behavior within 4 days of birth. Piglets sleep on average 10.5 h day 1 during the first 5 weeks. In nature, sows and their piglets stay together for several weeks. Piglets start showing play behavior (tossing and waving the head, spinning around) when they are 2-days old and will reach a peak between 2 and 6 weeks of age. The play behavior facilitates socialization with group members. Abnormal Behavior Abnormal behaviors are generally considered indicators of compromised welfare in animals. Abnormal behavior is defined as a clear deviation from the normal behavior expressed by majority of the members of the species when they are allowed to perform their full range of behaviors. Abnormal behavior may be harmful to animal itself and/or to other members in the group. Provision of manipulable substances and thereby avoiding barren environments will help reduce most of the abnormal behaviors. Common abnormal behaviors in pigs are described as follows. Stereotypy
Stereotypy is a repetition of sequence of movements without any apparent reason. The repetition may be regular or irregular and may be short or long. Stereotypies are linked to the dopamine release systems in the brain that control body movements. Stereotypies are generally exhibited when the animal has no control over its environment, causing frustration. The argument that stereotypy is part of an animal’s coping mechanism has not been widely accepted. Even if it is so, the indication is that welfare is compromised. Sham chewing (pig imitates chewing movements even when there is no food to chew, characterized by chewing, mouth gaping, and frothing and foaming of saliva), bar biting (animal opens and closes its mouth around a bar/metal piping of the stall, engaging the tongue and teeth with surface and performing chewing movements) are common stereotypies noticed in pigs especially in stall-housed pigs. Continuous repeated pressing of the drinker by some sows is also considered to be a stereotypy. Provision of straw or other manipulable material has shown to reduce most of the stereotypic behaviors. Tail biting
Tail biting is an abnormal behavior that occurs mainly in grow-finish pigs and that is directed to group mates. Crowding and consequent inadequacy of feeder and waterer spaces in group housing is associated with tail biting. Environmental factors such as high temperature, humidity, and noise may exacerbate the situation. However, lack of oral stimulation is suggested to be the major reason for this abnormal behavior. The incidence of tail biting is increased among pigs housed without bedding on
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slatted floors and ones that are fed automatically. Hunger also predisposes pigs to tail biting. The bleeding from tail biting stimulates further tail biting. Provision of rooting materials has been shown to reduce tail biting. Docking may reduce tail biting though it may lead to another abnormal behavior, ear chewing. Vulva biting
This is very common in ESF systems where the hungry sows are forced to wait to access the feeder. As in tail biting, the bleeding from the wound stimulates further biting. Anal massage
Anal massage is an abnormal behavior noticed in growing pigs, especially in docked pigs. Providing objects to chew and root will help to minimize this problem. Belly nosing
It is the up-and-down movement of the snout and the top of the nose on the belly of other pigs, on the soft tissue between their hind legs and between their forelegs. This is common in early weaned piglets, especially those that continue to show teat-seeking behavior, which gets directed toward other piglets. Cannibalism
This is an abnormal behavior mostly seen in sows with first litters where the sow may kill and eat her own piglets. In its mildest form, the hyper-reactive sow may accidentally crush and kill the piglets which are then eaten partially or fully. In severe forms, the sow tries actively to avoid piglets and approaching piglets are attacked, killed, and eaten fully or partially. Once started, cannibalism usually stops only after the death of the entire litter. Cannibalism is associated with hyperexcitability of the sow following farrowing, due to the novelty of the farrowing environment. Providing bedding before farrowing and allowing sows to build nests may reduce cannibalism. Pigs are highly motivated to explore their environment and spend 75% of their active time in foraging-related behavior. Provision of concentrates in a single location as in confined systems requires the animal to satisfy all its food intake needs within a short time, while not satisfying the motivation to explore and forage. In the barren environment, these behavioral needs are redirected at unsuitable targets such as pen mates. Lack of substrates is the major reason for abnormal behaviors such as tail biting and ear chewing. Studies have suggested that even the modern swine breeds retain the behavioral features of wild boars. Most of these natural behaviors are controlled by internal factors, and therefore swine welfare is compromised by a lack of opportunities to perform the behaviors that they are strongly motivated to perform.
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Pigs: Behavior and Welfare Assessment
Sickness Behavior Sickness behavior is defined as the expression of the adaptive reorganization of the priorities of the host during an infectious period. The major feature of sickness behavior is a general decrease in activity (immobility, sleepiness, reduced food and water intake). Sickness behavior may be interrupted in response to important strong stimuli (e.g., a sick sow may respond to a newborn piglet). The reduction in activity helps the animal conserve energy, and spend more time resting and sleeping. However, reduction in activity may not occur in all cases. A sick animal will try to move away from its group. This helps the animal to be away from the disturbances of its group mates and minimizes the chances of transmission of disease. It is argued that the behaviors shown by sick animals are part of a strategy to fight disease. Behaviors such as play, grooming, sexual behavior will be reduced in illness, as animals divert resources for maintaining body temperature and combating pathogens.
Using Behavioral Principles to Improve Pig Welfare Pigs prefer to live in large static groups with plenty of space and opportunities to perform many of their natural motivations. However, it is a practical and economic challenge to offer these facilities under commercial farming. For instance, space is a limiting factor in farms. Similarly, dynamic grouping with frequent mixing of pigs may be required to ensure better facility use. However, a knowledge of swine behavior can be successfully utilized to mitigate the threats to the welfare of domestic swine. Aggression is unavoidable when unfamiliar pigs are mixed together. However, the extent of aggression is determined by the method of feeding, and the amount and quality of space. Similarly, aggression at mixing can be influenced by design of the system and by management techniques. For instance, allowing small subgroup formation has been indicated to reduce aggression at mixing. The shape of the pen is also important in determining the level of aggression, with higher aggression in circular pens, and lower aggression in pens with a solid barrier. Aggressive interactions can be reduced over the short term by mixing pigs after sunset, administering some pharmacologic compounds, and the presence of boar at the time of mixing. Space availability is another issue as pigs in groups require space to show submissive behavior (e.g., running away). Providing the space necessary to perform this behavior will ensure quick establishment of social hierarchy and stability in the group. It has been suggested that the psychological stress associated with nonresolvable aggressive interactions among stall-housed sows is a chronic stressor.
Unique Problems in Assessing Welfare by Behavior Obviously, welfare is a multifactorial concept. Therefore, behavior alone cannot be an adequate indicator of welfare in animals. However, given that behavior change is the first overt and perhaps the major indicator of compromised welfare, we are justified in using it in animal welfare assessment. At the same time, it is important to remember that we as humans are ascribing meanings to the behaviors of another species, and to that extent our interpretations can be erroneous. Often, behavioral pathologies are used as indicators of compromised welfare. However, it is important to understand the positive behaviors in animals and their link to welfare. Many times, stress physiology is used to assess the existence of a positive state or at least the absence of a negative emotional state in animals. However, physiological parameters such as heart rate, respiration rate, and cortisol levels are influenced by factors not adversely affecting the welfare of the animals. For instance, sexual excitement can increase the heart rate and respiration rate without any adverse effect on the welfare of the animals. Individual differences, developmental changes, and diurnal variations in measures can also affect the interpretation of the final result. Thus, subjective assessment is also frequently needed for successful welfare assessment. Nonetheless, the extent to which a human observer can accurately assess the mental feeling of the animal is debatable. This is a serious limitation in using behavioral indicators for welfare assessment. Motivational studies evaluating the animal’s ‘willingness to work’ have been suggested as useful in assessing the state of the animal. Even then the correct interpretation demands appropriate experimental designs and sophisticated operant equipment. Even though preference tests are used in housing system studies, they are not perfect. The main limitation is that the results are unique to the testing situation. The behavioral choice of the animal may vary with the duration of exposure. Above all, it may be difficult to establish a scientific rationale for the choices made by the animal because those choices may not always be the best for the subject. The multifactorial nature of animal welfare also raises the issue of how to weight those factors. Often, a higher importance is given to factors which humans value had they been exposed to such a welfare threat. It is also possible that different indicators may provide conflicting interpretations. For instance, physiological and behavioral indicators provide different assessment of the pain associated with castration. Similarly, behavioral and health indicators have come up with different conclusions regarding the welfare implications of providing bedding for pigs. Another difficult issue, even when positive behaviors are used to assess the welfare status, is the level of such
Pigs: Behavior and Welfare Assessment
behaviors. For example, allogrooming is generally considered as a positive behavior in social groups of pigs. Nevertheless, excessive levels of allogrooming activity may not necessarily reflect positive states of the animal as they are likely to disturb the receiver. Obviously, there are no objective indicators to assess this and no gold standard has been established. Similarly, the ability of the animal to perform various postural behaviors is critical with respect to its welfare. But there are no scientifically valid numbers available regarding the duration or frequency of postural behaviors, leaving the assessor to resort to subjective judgments.
Areas Where More Research Is Needed Obviously, all the limitations mentioned earlier warrant further research. However, there are promising areas that are expected to advance human knowledge about animal behavior. These have the potential to improve the welfare of domestic animals. One little-researched area is sickness
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behavior and its value as a disease indicator. Similarly, studies are needed to understand how to assess the positive experiences in animals that are suggested to be important components of good welfare. This issue is crucial because well being is not merely the absence of negative effects, but instead, predominantly the presence of positive effects. Affiliation (closer relationship between certain pairs of individuals) is a type of social behavior exhibited by many farm animal species. Affiliative behavior has been suggested to create a ‘positive mood’ in animals. However, the number of studies focusing on this behavior is considerably less than those involving social competition. Our efforts to focus on negative behaviors will only enable us to help the animal meet its needs and thereby avoid suffering. Research is also needed to understand how to use positive experiences to a better quality of life to the animals and to improve their health. See also: Beyond Fever: Comparative Perspectives on Sickness Behavior; Self-Medication: Passive Prevention and Active Treatment; Welfare of Animals: Introduction.