Management factors affecting gestating sows’ welfare in group housing systems — A review

Article information

Anim Biosci. 2022;35(12):1817-1826
Publication date (electronic) : 2022 October 11
doi :
1Department of Animal Science, College of Agriculture and Life Sciences, Gyeongsang National University, Jinju 52725, Korea
*Corresponding Author: Sang-Hyon Oh, Tel: +82-55-772-3285, Fax: +82-55-772-3689, E-mail:
Received 2022 July 25; Revised 2022 September 8; Accepted 2022 October 1.


Public concern on the methods of raising food-producing animals has increased, especially in the last two decades, leading to voluntary and mandated changes in the animal production methods. The primary objective of these changes is to improve the welfare of farm animals. The use of gestational stalls is currently a major welfare issue in swine production. Several studies assessed the welfare of alternative housing systems for gestating sows. A comparative study was performed with gestating sows housed in either individual stalls or in groups in a pen with an electronic sow feeder. This review assessed the welfare of each housing system using physiological, behavioral, and reproductive performance criteria. The current review identified clear advantages and disadvantages of each housing system. Individual stall housing allowed each sow to be given an individually tailored diet without competition, but the sows had behavioral restrictions and showed stereotypical behaviors (e.g., bar biting, nosing, palate grinding, etc.). Group-housed sows had increased opportunities to display such behavior (e.g., ability to move around and social interactions); however, a higher prevalence of aggressive behavior, especially first mixing in static group type, caused a negative impact on longevity (more body lesions, scratch and bite injuries, and lameness, especially in subordinate sows). Conclusively, a more segmented and diversified welfare assessment could be beneficial for a precise evaluation of each housing system for sows. Further efforts should be made to reduce aggression-driven injuries and design housing systems (feeding regimen, floor, bedding, etc.) to improve the welfare of group-housed sows.


Animal production management has changed significantly across the European Union (EU) over the latter half of the 20th century [1]. During this period, pork production intensified, implying that the total number of breeding animals has increased, while the ratio of animal breeding farms has drastically decreased [2]. This phenomenon appears to be strongly related to increased household income. With global economic development, per capita income has grown rapidly, leading to significant changes in the patterns of food consumption—from grains to livestock-derived products [3]. To meet consumer demand, large numbers of animals are moved to indoor housing systems with lower space allowances, and the use of prophylactic medicines and growth promoters has increased [4]. This intensification of the industry increased productivity but decreased the monetary value of any given animal [5]. Widespread concern about farm animal welfare was highlighted in response to this campaign because evidence showed that keeping farm animals in intensive conditions may lead to a reduction in the welfare status of animals [6]. Pigs (Sus scofa domesticus) are the most intensively reared mammals in the world [7], with approximately 1.3 billion pigs slaughtered annually for meat. Although legislation to optimize conditions for the protection of pigs has recently surpassed that required by EU law (e.g., Animal Welfare Act 2006), it does not solve all the welfare concerns associated with conventional pig rearing [1].

Several studies suggested ways to protect livestock against confinement conditions. In gestating sows, individual stall management is widely used for the ease of artificial insemination, low capital cost, and minimization of overt aggressive behaviors [8]. However, the restriction of movement, impossibility of performing normal feeding, and disruptive patterns of behavior cause welfare problems, such as the development of stereotypes, chronic stress, lameness, and decubital ulcers [9]. Several studies compared the different indicators of welfare and productivity in stalls and in modern commercial group housing systems. Group-housed sows with an electronic sow feeding (ESF) system have similar or improved productivity compared with sows housed in stalls [10]. Furthermore, no differences in stress-related serum cortisol concentrations were evident between sows housed in stalls and those housed in groups [11,12].

This review explores the definition of animal welfare, parameters for welfare assessment, and rapidly accumulating data concerning the impact of the housing systems on welfare in gestating sows. The main factor affecting welfare issues include group housing for gestating sows. Welfare during the other phases of pig production (nursery, growing-finishing pigs, and farrowing sows) is outside the scope of this review


Animal welfare started with the publication of the Brambell report on the welfare of farm animals, issued by the World Organisation for Animal Health (formerly the Office International des Epizooties; OIE) in 1965 [13]. In the report, animal welfare is defined as “the physical and mental state of an animal in relation to the conditions in which it lives and dies” [13]. Since then, considerable research has been conducted on animal welfare problems involving scientific fields of interest, such as the development of welfare assessment in various environmental conditions, as well as on more fundamental questions linking the biological bases of welfare and stress [14]. Freedom plays a key role in animal husbandry. In fact, the Farm Animal Welfare Council defined knowledge about the needs of animals, which is related to the proposal to give animals some freedom (Table 1).

The five freedoms as the fundamental experience goals for animals

According to the study of Carenzi and Verga [14], there are three aspects of welfare evaluation. The first approach emphasizes the biological functions of the organism, such as growth and reproductive performance, as well as its health status and behavioral characteristics. Behavior reflects the foremost response to environmental stimuli and may provide a clear signal of stressors. Qualitative welfare levels reflect the absence of distress or a strong stress response [15]. A second approach suggests that the relationship between stress and welfare stress in terms of psychological aspects, considering feelings as a key element in determining quality of life. The third approach emphasizes natural living, insisting that animals should be allowed to live according to their natural attitudes and behaviors, mainly developing and using their natural adaptations. However, due to the domestication process, domestic animals differ in many ways from their co-specifics, and it is difficult to assess welfare levels in a scientific way. A more comprehensive approach to animal welfare, categorized into four main issues, was proposed by Dockès and Kling-Eveillard [16]:

  • i) Biological and technical definitions stress the fundamental needs of animals and their freedom, as well as the possibilities to cope with environmental challenges.

  • ii) Regulation approaches, which recognize the animal as a sensitive being and as such must be put in conditions “compatible with the biological needs of the species.”

  • iii) Philosophical approaches, which consider the “status of the animal” and its role in human society.

  • vi) Communication between humans and animals is of great importance to the farmer-animal interaction and its effects on industrial breeding systems.


Welfare criteria is a multifactorial concept that relies on the analysis of the interaction between animals and their environment, which include behavior and the biology between the hypothalamic-pituitary-adrenocortical (HPA) axis and the autonomic nervous system (ANS), as well as animal’s consequences on production traits and possibly the health status [17]. This is the reason the welfare categories are not uniformly agreed upon by various stakeholders, including scientists, producers, and consumer protection unions. Based on this standard, welfare methods can be categorized into three types: animal-, resource-, and management-based. Welfare Quality is one of the most widespread animal welfare assessment protocols for animal-based indicators, including lameness, body condition score, qualitative behavior assessment, and the human-animal relationship test [18]. In this review, we focus on welfare assessment based on resource indicators, as followed by McGlone et al [19].


Various biological systems, such as the cardiovascular system, gastrointestinal system, exocrine system, and adrenal medulla, are controlled and influenced by the ANS during stress [20]. However, it is controversial whether stress activation of the ANS significantly affects the long-term welfare of an animal, owing to the relatively short duration of the biological effect on autonomic responses [21]. In fact, the plasma levels of catecholamines are extremely sensitive to handling, and hence, more surgical blood sampling methods, such as direct venous puncture or chronic catheter, must be considered [22]. Fernández et al [23] suggested that this short-term acute response can be diagnosed using various measurements, such as heart rate, blood pressure, plasma glucose, and fatty acid levels. Furthermore, the value of monitoring ANS activity is subject to various factors, such as locomotion, physical activity, and/or feed intake [24]. The concentrations of plasma glucose and fatty acids represent the energy balance between the mobilization of energy stores and use of energetic metabolites, whereas the concentration of serum lactic acid reflects anaerobic metabolism [25]. These metabolic measurements are frequently connected with assays for the determination of circulating enzyme activity, such as transaminases and creatine kinase, which are widely used to detect susceptibility to stress in pigs [26].

Contrastingly, HPA activity, with the release of cortisol, a cholesterol-derived steroid synthesized in the fascicular zone of the adrenal cortex under the control of the pituitary hormone adrenocorticotropic hormone, released in the general circulation to reach its receptors in tissues, has a broad and long-lasting effect on the body [27]. Cortisol exhibits catabolic activity in peripheral tissues and anabolic activity in the liver, including gluconeogenesis and protein synthesis [28]. Since cortisol also reduces the entrance of glucose into cells, it increases blood glucose and insulin secretion, resulting in the storage of energy as fat in adipose tissue. Consequently, this increases fat deposits at the expense of tissue proteins [29]. Furthermore, cortisol increases appetite by stimulating the arcuate and ventromedial hypothalamus in the brain [30]. This is frequently the case in homeostatic regulations; the increase in energy availability is a coordinated process via peripheral and central mechanisms [31]. Although the features of the HPA axis are not specifically documented in pigs, cortisol is highly susceptible to a diurnal cycle that is genetically determined by light and feed intake [32] (Figure 1).

Figure 1

Diurnal changes in plasma cortisol of gestating sows fitted with an indwelling jugular catheter. The meal-induced release of cortisol is clearly visible [32].


Behavior is the primary way of interaction; therefore, it can be a sensitive indicator of the animal’s perception of environmental changes [33]. Various behavioral patterns often reflect the first level of response of an animal to a stressful environment. Thus, behavior is used extensively to analyze environmental needs and preferences [34]. Additionally, it is also a classical symptom in the examination of health problems, such as general behavioral depression accompanying fever, known as sickness behavior, or lameness indicative of locomotor problems [35].

In addition to sickness-related behavior, other changes in the duration and frequency of normal behavior are recognized as indicators of mental suffering [36]. Furthermore, Cook et al [36] noted that there are numerous possible signs of stress, including startle or defense response, avoidance, excessive aggression, stereotypic behavior, and lack of responsiveness. Although not all these various behaviors are signs of poor welfare, they can be a warning sign if accompanied by other symptoms [37]. Redirected injurious behaviors, such as tail biting in pigs, correlated with a lack of exploratory activity, are abnormal behaviors that may easily lead to pain. Thus, acceptance of the behavioral need for this exploration, as well as frequencies of redirected behaviors, can be used as indicators of welfare [38,39].

Aggressive behaviors are major expressions of the social interaction of pigs [40]. The most aggressive behavior appears in relation to feed competition or mixing [4143]. Such behavior can be observed in intensive commercial pig housing systems, especially when unknown pigs are mixed into new groups [44]. Aggressive behavior occurs in several circumstances, such as body weight difference, various space or group sizes, or familiarity [33,45]. Aggressive encounters often result in skin injury and can have immunosuppressive effects [46].

An animal displaying stereotypical behavior repeats a relatively invariant sequence of behaviors that has a purposeless function [47]. The impossibility of displaying a behavioral need can also lead to the appearance of stereotypies. Various abnormal behaviors occur in farm animals, including bar biting in confined sows, tongue rolling in cows, and crib-biting in horses [48].


Although the relationship between production and welfare is not simple and difficult to interpret, performance parameters provide an overview of the problems that reflect optimum welfare [49,50]. Practices to improve production via the use of growth promoters are questioned because they may have a detrimental impact on welfare or mask the negative impact or poor welfare on production performance [51]. Therefore, it is better to approach the welfare assessment of performance in terms of health status rather than productivity. Representative parameters include mortality in growing-finishing pigs and reproductive performance of sows (stillborn, mummy, weaned pigs, culling rate, farrowing rate, and weaning to estrus interval). Mortality rate is influenced by various factors, such as housing conditions, management, group size, and stockmanship [52]. In sows, poor reproductive performance may be related to stress. A possible explanation reported by Wan et al [53] is that glucocorticoid hormones reduce the activity of sex neuroendocrine systems and therefore reduce the efficiency of reproductive performance. In finishing pigs, agonistic productivity can have detrimental effects on welfare and reduce weight gain [54]. They also compromise pork quality, giving pork low pH and pale, soft, and exudative, which reflects the economic crisis underlying pig production [55].


A major public concern regarding farm animal welfare is focused on gestating sows (Council Directive 91/630/EEC, 1991). Under commercial conditions, gestating sows are predominantly accommodated in gestation stalls, which are both physically and psychologically detrimental to sows [19,56]. In fact, much compelling evidence exists that the European Union’s (EU) Agriculture Council, which consists of agriculture ministers from 15 member countries of the EU, issued a directive addressing gestation stalls (Council Directive 2001/88/EC, herein referred to as the “EU Pigs Directive”) that will apply to newly built facilities as of 2003 and all other facilities as of 2013. The directive bans the use of stalls after the fourth week of pregnancy and tethers completely. Nevertheless, the major pork-producing countries (e.g., East and South-East Asia, USA, and South America) still use stall housing because of the ease of artificial insemination, low capital cost, individual feeding, and minimization of aggressive behavior [8]. However, stall housing has a negative effect on muscle weight and bone strength [57], decubital ulcers, chronic diseases, and stereotypes, which indicates poor welfare of sows [9].

There are advantages and disadvantages to group housing and individual stall systems. Individual stalls can reduce labor costs, are more manageable, have earlier morbidity detection, and can control feed intake [58]. Additionally, the stall protects the sow from aggressive encounters that normally occur during the regrouping of sows in group pens, which occur throughout a sow’s lifetime [59]. Contrastingly, the major difference between the group housing system and stall management is that the former provides freedom of movement by providing enough space to turn around, lie down, stand up, stretch limbs, and groom [60]. This is commonly known as dynamic space, or the space necessary to make postural adjustments or turn around [59]. Restricting the ability of the sow to walk and turn around may affect their health, performance, and overall wellbeing [58,60].


Space allowance

The minimum space requirement for a sow in group housing remains controversial. The European Food Safety Authority [61] describes the three types of space required to aid the estimation of the levels of space required by pigs: static, behavioral, and interaction space. The static space required for pigs to lie, or stand can be calculated using the equation A = k×W0.666, where A is the area in m2, W is body weight in kg, and k is a constant depending on the posture of the animal. Examples of k = 0.019 for sternal lying (and standing) and k = 0.047 for fully recumbent pigs [62].

Many scientific studies related to space allowance in pigs measured the occurrence of aggressive interactions as an important outcome of feeding system types [6366]. They concluded that the effect of floor space on aggression particularly increased early after mixing. In gilts, Barnett et al [63] observed that on days 2 to 54 after mixing, increasing space reduced aggressive behaviors, such as bites and butts. Similarly, the number of threats, withdrawals, and head interactions, including bite and nose interactions, were reduced with increasing space on days 6 and 7 after mixing in sows [64]. Furthermore, Remience et al [66] found that nonreciprocal aggression on days 3 and 8 after mixing was greater in pregnant sows in a smaller floor space, although reciprocal aggressive behavior (bites or knocks) did not differ. For sows mixed soon after insemination, increasing space reduced feeding aggression on day 2 after mixing, but not on day 8 [67].

Increased aggressive behavior was correlated with decreased space allowance. Weng et al [64] reported that more injuries were observed with greater space restrictions in the group housing system. Similarly, Remience et al [66] noted that more fresh superficial injuries and deep skin injuries were reported when less space (2.25 versus 3.0 m2/sow) was provided in ESF group housing. Furthermore, Salak-Johnson et al [65] stated that skin injuries increased as floor space decreased. However, Hemsworth et al [67] concluded that although space affected aggression and stress, it did not affect skin injuries. These conflicting results may be due to different experimental conditions, such as floor feeding, ESF, and static and dynamic groups.

The immune system is one of the mechanisms developed by organisms to defend against environmental challenges and other perceived threats [68]. Several studies concluded that chronic stress exerts a general immunosuppressive effect that suppresses or withholds the ability of the body to initiate a prompt and efficient immune reaction [69]. This is due to high levels of corticosteroid production during chronic stress, which produces an imbalance in corticosteroid levels [70]. Plasma cortisol levels and changes in leukocyte populations are the most common physiological parameters used to measure farm animal welfare [19]. A study by Salak-Johnson et al [68] found differences in cortisol, neutrophil, and lymphocyte populations, and neutrophil-to-lymphocyte (N:L) ratio, with sows housed at the greatest floor space allowance having the lowest N:L ratio but the highest plasma cortisol. Contrastingly, most studies found no difference in plasma cortisol [12,71] or immune activity, more specifically N:L ratio [12,72] among sows housed in stalls or pens.

Group size

Group size is defined by the number of sows in a pen rather than by the amount of space allotted to each sow [73]. It was reported earlier that aggression increases in large groups due to the establishment of a dominance hierarchy [34,74]. However, recent reviews concluded that there is no evidence to suggest that there is more aggression in large groups of up to 40 and 300 sows in experimental settings and commercial conditions, respectively [58,75]. This also supports the findings of Hemsworth et al [67], who indicated that there was no statistical difference in the frequency of aggression in group-housing sows in the early gestation period (days 2 and 8 after mixing) into groups of 10, 30, and 80. Therefore, the author speculated that group size is correlated with the ability to socialize sows [67]. In large groups, where individual recognition is less likely, animals use methods other than aggression to establish social dominance, such as body size [76]. Group size had no effect on reproductive performance [67,74], as well as serum cortisol concentration [67]. Anil et al [77] noted that sows exposed to the aggression associated with mixing and the ESF before implantation may have a lack of difference in reproductive performance between the different size groups.

Group type

Under commercial conditions, gestating sows can be managed in either static or dynamic groups. For the static groups, all sows in a group were introduced on the same day and remained until the entire group was moved to the farrowing facility. Static grouping involves forming a pen group once without adding more females after the group is established. In dynamic groups, small groups of sows are added to a larger existing group periodically throughout gestation, and groups are removed periodically as sows move farrowing. A new bout of aggression occurs each time a new group is added [78]. However, sows in large dynamic groups are shown to adopt a more tolerant and passive response to unfamiliar animals [79].

Although few studies pointed out that greater aggressive behavior originates from frequent mixing in dynamic groups [34,58,80], other findings do not support this interpretation. According to a study by Van der Mheen et al [81], sows in large dynamic groups (50 sows) consumed their individual ration in smaller portions due to disturbances in the feeders compared to that in small static groups (13 sows). Additionally, these authors found that sows in dynamic groups recorded higher incidences of skin scratches, but no differences between treatments were observed in pregnancy rates, litter size, or litter weight [81]. In agreement with this, Anil et al [82] found that although skin injury scores were greatest in the dynamic group both in general and 2 weeks after mixing, there were no effects on aggression, cortisol concentrations, farrowing performance, and longevity. Furthermore, a study by Strawford et al [83] found no differences in aggression, skin injuries, and cortisol concentrations between sows in static and dynamic groups with ESF.

Feeding regime

It is considered that a restricted amount of feed is commonly provided to breeding sows to prevent excess BW gain and fat deposition, which can cause farrowing and locomotion problems and subsequently reduce reproductive performance [84]. In the pork industry, it is generally considered that a restricted level of feeding during gestation is sufficient for maintenance and fetal development, suggesting that animals do not have a negative energy balance [85]. However, limited feeding results in more competition for feed or access to feeding areas, and the development of stereotypies [58]. In the condition of group housing, there is no clear evidence in the literature on increased aggression, stress, or injuries associated with restricted feeding levels. According to a study by Spoolder at al [86], although there were no effects on aggression or skin injuries, grouped sows fed 1.8 kg (23 MJ digestible energy (DE)/d) in “lock-in” stalls spent more time standing and manipulating bars and chains after feeding than those that were fed 3.2 kg (40 MJ DE/d). Bergeron and Gonyou [87] found that sows fed either a high-energy diet (23.7 MJ DE/kg) or a “high-foraging” diet (a standard diet [14.0 MJ DE/kg] but with a device in the feeder that increased the feeding time) spent less time active and displaying stereotypies than sows fed with a standard diet (14.0 MJ DE/kg). Therefore, a lack of energy from diet and time spent feeding may contribute to the development of stereotypies [85]. However, although increased feeding times are shown to reduce sow hunger, sequential feeding systems such as ESF can cause crowding, thereby reducing the overall feeder capacity [88].

The type of feeding system affects the level of aggression related to feed competition [75]. There are three representative feeding types in the group-housing system: floor feeding, partial stalls, and ESF. Floor feeding is the simplest and cheapest among the systems. This system allows sows to feed simultaneously, and thus fulfills some elements of natural feeding behavior. However, variation in feed consumption between dominant and subordinate sows is also observed in floor feeding systems, causing subordinates to suffer from undernourishment and low weight gain [89]. Contrastingly, partial stall reduces aggression and plasma cortisol concentrations in the long term in group-housed gestating gilts [90,91]. Most welfare concerns in this system are the incidence of vulvar biting. Andersen et al [91] found that sows housed in pens with full-body feeding stalls had increased vulva bites and suggested that feeding arrangement influences nature as well as the amount of aggression. Although floor feeding is competitive, gaining access to feeding stalls can also lead to competition and aggression between group-housed sows [73]. The most advantageous group housing system that deals with the individual feed consumption of sows is the ESF. This allowed for the greatest possible control over individual sow intake. However, this system forces the sows to feed in sequence, and as such, the sows queue at the ESF entrance gate. These findings support recent work by Olsson et al [92], who observed that approximately 4 to 6 sows often queue at the ESF entrance, although one-third of queued sows have already eaten daily feed rations. Consequently, preventing queuing was identified as an important development for improving welfare in ESF systems [82].


Although the influence of bedding quality on welfare, health, and performance of animals is not extensively studied, the most common enrichment and bedding materials for group-housed sows reported in the literature are straw [93] or rice hulls [94]. In fact, straw offers excellent possibilities for diverse manipulations: to root or scratch in, to chew, and to eat. Andersen et al [91] found that in group-housed sows, the supply of a bedding substrate reduced the frequency of abnormal gait compared to sows raised on a slatted floor. Beddings also play an important role in group housing designs, as they absorb excreta and are used to enhance the thermoregulatory abilities in sows [95]. Therefore, group housing with straw bedding is almost always associated with large dynamic groups and ESF feeding [75]. This suggests that in large groups with a tendency for higher incidences of aggression, enrichment and bedding may be an effective means of improving sow welfare [73]. However, the use of straw is not without its disadvantages, mainly due to cost, increased labor, hygiene concerns, and most importantly, incompatibility with manure and drainage systems [96]. Bench et al [88] stated that several factors make it difficult to evaluate the welfare relevance of straw from the scientific literature: i) the variation in the composition, structure, quality, and quantity of straw; ii) no scientifically authorized or qualified assessment of animal welfare on the effect of straw; iii) lack of specific investigation on the welfare impact of straw; and v) the importance of straw with the age of the animal and their housing conditions and management.


In this review, the advantages and disadvantages of welfare indicators are highlighted and broadly discussed. For gestating sows, group-housed sows negatively influence aggressive behavior during the establishment of a social hierarchy, causing a negative impact on longevity (more body lesions and lameness). Sow housing in individual stalls leads to more stereotypical behaviors. However, there were inconsistent results on reproductive performance across studies. More validated and reliable resource-based sow welfare assessment protocols should be developed with the help of farmers, experts, stakeholders, and consumers.


A part of this manuscript was presented in the Ph.D. dissertation of Jae-Cheol Jang (2016).



We certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.


The authors received no financial support for this article.


1. Tawse J. Consumer attitudes towards farm animals and their welfare: a pig production case study. Biosci Horiz 2010;3:156–65. .
2. Blokhuis HJ, Jones RB, Geers R, Miele M, Veissier I. Measuring and monitoring animal welfare: transparency in the food product quality chain. Anim Welf 2003;12:445–55.
3. Huang JK, Bouis H. Structural changes in the demand for food in Asia: empirical evidence from Taiwan. Agric Econ 2001;26:57–69. .
4. Fraser D. Assessing animal welfare at the farm and group level: the interplay of science and values. Anim Welf 2003;12:433–43.
5. Winter M, Fry C, Carruthers SP. European agricultural policy and farm animal welfare. Food Policy 1998;23:305–23. .
6. Harper GC, Makatouni A. Consumer perception of organic food production and farm animal welfare. Br Food J 2002;104:287–99. .
7. Arey D, Brooke P. Animal welfare aspects of good agricultural practice: pig production Petersfield, UK: Compassion in World Farming Trust; 2006.
8. Jang JC, Jung SW, Jin SS, Ohh SJ, Kim JE, Kim YY. The effects of gilts housed either in group with the electronic sow feeding system or conventional stall. Asian-Australas J Anim Sci 2015;28:1512–8. .
9. Scientific Veterinary Committee. 1997 The welfare of intensively kept pigs. In : Report of the Scientific Veterinary Committee, Animal Welfare Section, to the Comission of the European Union. Doc. XXIV/ScVc/0005/1997; 1997 September 30; Brussels, Belgium.
10. Bates RO, Edwards DB, Korthals RL. Sow performance when housed either in groups with electronic sow feeders or stalls. Livest Prod Sci 2003;79:29–35. .
11. Barnett JL, Hemsworth PH, Newman EA, McCallum TH, Winfield CG. The effect of design of tether and stall housing on some behavioural and physiological responses related to the welfare of pregnant pigs. Appl Anim Behav Sci 1989;24:1–12. .
12. von Borell EH, Morris JR, Hurnik JF, Mallard BA, Buhr MM. The performance of gilts in a new group housing system: endocrinological and immunological functions. J Anim Sci 1992;70:2714–21. .
13. Brambell Report. Report of the Technical Committee to enquire into the welfare of animals kept under intensive livestock husbandry systems London, UK: Her Majesty’s Stationery Office; 1965.
14. Carenzi C, Verga M. Animal welfare: review of the scientific concept and definition. Ital J Anim Sci 2007;8(suppl 1):21–30. .
15. Broom DM. Indicators of poor welfare. Br Vet J 1986;142:524–6. .
16. Dockès AC, Kling-Eveillard F. Farmers’ and advisers’ representations of animals and animal welfare. Livest Sci 2006;103:243–9. .
17. Ulrich-Lai YM, Herman JP. Neural regulation of endocrine and autonomic stress responses. Nat Rev Neurosci 2009;10:397–409. .
18. Welfare Quality®. Welfare Quality® assessment protocol for pigs (sows and piglets, growing and finishing pigs) Lelystad, Netherlands: Welfare Quality® Consortium; 2009.
19. McGlone JJ, Borell EH, von Deen J, et al. Compilation of the scientific literatures comparing housing systems for gestating sows and gilts using measures of physiology, behavior, performance and health. Prof Anim Sci 2004;20:105–17. .
20. Cannon WB. Organization for physiological homeostasis. Physiol Rev 1929;9:399–431. .
21. Moberg GP. Problems in defining stress and distress in animals. J Am Vet Med Assoc 1987;191:1207–11.
22. Fernández X, Meunier-Salaun MC, Mormede P. Agonistic behavior, plasma stress hormones, and metabolites in response to dyadic encounters in domestic pigs: interrelationships and effect of dominance status. Physiol Behav 1994;56:841–7. .
23. Fernández X, Meunier-Salaun MC, Ecolan P, Mormede P. Interactive effect of food deprivation and agonistic behavior on blood parameters and muscle glycogen in pigs. Physiol Behav 1995;58:337–45. .
24. Villé H, Bertels S, Geers R, et al. Electrocardiogram parameters of piglets during housing, handling and transport. Anim Sci 1993;56:211–6. .
25. Guise HJ, Riches HL, Hunter EJ, Jones TA, Warriss PD, Kettlewell PJ. The effect of stocking density in transit on the carcass quality and welfare of slaughter pigs: 1. Carcass measurements. Meat Sci 1998;50:439–46. .
26. Pérez MP, Palacio J, Santolaria MP, et al. Effect of transport time on welfare and meat quality in pigs. Meat Sci 2002;61:425–33. .
27. Reichlin S. Williams textbook of endocrinology. In : Wilson JD, Foster DW, Kronenberg HM, Larsen PR, eds. Williams textbook of endocrinology 10Philadelphia PA, USA: WB Saunders Co; 1998. p. 165–248.
28. McMahon M, Gerich J, Rizza R. Effects of glucocorticoids on carbohydrate metabolism. Diabetes Metab Rev 1988;4:17–30. .
29. Sapolsky RM, Romero LM, Munck AU. How do glucocorticoids influence stress response? Integrating permissive, suppressive, stimulatory, and preparative actions. Endocr Rev 2000;21:55–89. .
30. Leshin LS, Barb C, Kiser TE, Rampacek GB, Kraeling RR. Growth hormone-releasing hormone and somatostatin neurons within the porcine and bovine hypothalamus. Neuroendocrinology 1994;59:251–64. .
31. Tempel DL, Leibowitz SF. Adrenal steroid receptors: interactions with brain neuropeptide systems in relation to nutrient intake and metabolism. J Neuroendocrinol 1994;6:479–501. .
32. Hay M, Meunier-Salaün MC, Brulaud F, Monnier M, Mormède P. Assessment of hypothalamic-pituitary-adrenal axis and sympathetic nervous system activity in pregnant sows through the measurement of glucocorticoids and catecholamines in urine. J Anim Sci 2000;78:420–8. .
33. Rushen J. A difference in weight reduces fighting when unacquainted newly weaned pigs first meet. Can J Anim Sci 1987;67:951–60. .
34. Arey DS, Edwards SA. Factors influencing aggression between sows after mixing and the consequences for welfare and production. Livest Prod Sci 1998;56:61–70. .
35. Dantzer R, Kelley KW. Twenty years of research on cytokine-induced sickness behavior. Brain Behav Immun 2007;21:153–60. .
36. Cook CJ, Mellor DJ, Harris PJ, Ingram JR, Mathews LR. Hands-on and hands-off measurement of stress. In : Moberg GP, Mench JA, eds. The Biology of Animal Stress: Basic Principles and Implications for Animal Welfare Cambridge, MA, USA: CABI Publishing; 2000. p. 123–46. .
37. Mason GJ, Latham NR. Can’t stop, won’t stop: is stereotypy a reliable animal welfare indicator? Anim Welf 2004;13(Suppl):S57–69.
38. Day JEL, Burfoot A, Docking C, Whittaker X, Spoolder HA, Edwards SA. The effects of prior experience of straw and the level of straw provision on the behaviour of growing pigs. Appl Anim Behav Sci 2002;76:189–202. .
39. Guy JH, Rowlinson P, Chadwick JP, Ellis M. Behaviour of two genotypes of growing–finishing pig in three different housing systems. Appl Anim Behav Sci 2002;75:193–206. .
40. McGlone JJ. Influence of resources on pig aggression and dominance. Behav Processes 1986;12:135–44. .
41. Ewald PW, Carpenter FL. Territorial responses to energy manipulations in the Anna hummingbird. Oecologia 1978;31:277–92.
42. Armstrong DP. Aggressiveness of breeding territorial honeyeaters corresponds to seasonal changes in nectar availability. Behav Ecol Sociobiol 1991;29:103–11. .
43. Chapman MR, Kramer DL. Guarded resources: the effect of intruder number on the tactics and success of defenders and intruders. Anim Behav 1996;52:83–94. .
44. Meese GB, Ewbank RA. A note on instability of the dominance hierarchy and variations in level of aggression within groups of fattening pigs. Anim Sci 1972;14:359–62. .
45. Algers B, Jensen P, Steinwall L. Behaviour and weight changes at weaning and regrouping of pigs in relation to teat quality. Appl Anim Behav Sci 1990;26:143–55. .
46. Tuchscherer M, Manteuffel G. The effect of psycho stress on the immune system. Another reason for pursuing animal welfare (Review). Arch Anim Breed 2000;43:547–60. .
47. Fraser AF, Broom DM. Farm animal behaviour and welfare London, UK: Ballière Tindall. Print; 1990.
48. Bergeron R, Badnell-Waters AJ, Lambton S, Mason G. Stereotypic oral behaviour in captive ungulates: foraging, diet and gastrointestinal function. In : Mason G, Rushen J, eds. Stereotypic animal behaviour: fundamentals and applications to welfare 2nd Editionth ed. Wallingford, UK: CABI Publishing; 2006. p. 19–57.
49. Gregory NG. Animal welfare and meat science Wallingford, UK: CABI Publishing; 1998. p. 53–74.
50. Jones RB, Boissy A. Fear and other negative emotions. In : Appleby MC, Mench JA, Olsson IAS, Hughes BO, eds. Animal welfare Wallingford, UK: CABI Publishing; 2011. p. 78–97.
51. Mormède P, Lemaire V, Castanon N, Dulluc J, Laval M, Le Moal M. Multiple neuroendocrine responses to chronic social stress: interaction between individual characteristics and situational factors. Physiol Behav 1990;47:1099–105. .
52. Losinger WC, Heinrichs AJ. Management practices associated with high mortality among preweaned dairy heifers. J Dairy Res 1997;64:1–11. .
53. Wan R-Q, Pang K, Olton DS. Hippocampal and amygdaloid involvement in nonspatial and spatial working memory in rats: effects of delay and interference. Behav Neurosci 1994;108:866–82. .
54. Stookey JM, Gonyou HW. The effects of regrouping on behavioral and production parameters in finishing swine. J Anim Sci 1994;72:2804–11. .
55. Sellier P. Genetics of meat and carcass traits. In : Rothschild MF, Ruvinski A, eds. The Genetics of the Pig Wallingford, UK: CABI Publishing; 1998. p. 463.
56. Bracke MBM, Metz JHM, Spruijt BM, Schouten WGP. Decision support system for overall welfare assessment in pregnant sows. B. Validation by expert opinion. J Anim Sci 2002;80:1835–45. .
57. Marchant JN, Broom DM. Factors affecting posture-changing in loose-housed and confined gestation sows. Anim Sci 1996;63:477–85. .
58. Barnett JL, Hemsworth PH, Cronin GM, Jongman EC, Hutson GD. A review of the welfare issues for sows and piglets in relation to housing. Aust J Agric Res 2001;52:1–28. .
59. Gonyou HW. Experience with alternative methods of sow housing. In: Animal Welfare Forum: Sow Housing and Welfare. J Am Vet Med Assoc 2005;226:1336–9.
60. Jensen KH, Pedersen BK, Pedersen LJ, Jørgensen E. Well-being in pregnant sows: Confinement versus group housing with electronic sow feeding. Acta Agric Scand A, Anim Sci 1995;45:266–75. .
61. EFSA (European Food Safety Authority). Opinion of the Scientific Panel on Animal Health and Welfare on a request from the Commission related to welfare of weaners and rearing pigs: effects of different space allowances and floor. EFSA J 2005;268:1–19. .
62. Baxter M. Social space requirements of pigs. In : Zayan R, ed. Social space for domestic animals Dordrecht, the Netherlands: Martinus Nijhoff Publishers; 1985. p. 116–27.
63. Barnett JL, Hemsworth PH, Cronin GM, Newman EA, McCallum TH, Chilton D. Effects of pen size, partial stalls and method of feeding on welfare-related behavioural and physiological responses of group-housed pigs. Appl Anim Behav Sci 1992;34:207–20. .
64. Weng RC, Edwards SA, English PR. Behaviour, social interactions and lesion scores of group-housed sows in relation to floor space allowance. Appl Anim Behav Sci 1998;59:307–16. .
65. Salak-Johnson JL, Niekamp SR, Rodriguez-Zas SL, Ellis M, Curtis SE. Space allowance for dry, pregnant sows in pens: Body condition, skin lesions, and performance. J Anim Sci 2007;85:1758–69. .
66. Remience V, Wavreille J, Canart B, et al. Effects of space allowance on the welfare of dry sows kept in dynamic groups and fed with an electronic sow feeder. Appl Anim Behav Sci 2008;112:284–96. .
67. Hemsworth PH, Rice M, Nash J, et al. Effects of group size and floor space allowance on grouped sows: Aggression, stress, skin injuries, and reproductive performance. J Anim Sci 2013;91:4953–64. .
68. Salak-Johnson JL, DeDecker AE, Horsman MJ, Rodriguez-Zas SL. Space allowance for gestating sows in pens: Behavior and immunity. J Anim Sci 2012;90:3232–42. .
69. Huebner ES. Burnout among school psychologists: An exploratory investigation into its nature, extent, and correlates. Sch Psychol Q 1992;7:129–36. .
70. Salleh MR. Live events, stress and illness. Malays J Med Sci 2008;15:9–18.
71. Tsuma VT, Einarsson S, Madej A, Kindahl H, Lundeheim N, Rojkittikhun T. Endocrine changes during group housing of primiparous sows in early pregnancy. Acta Vet Scand 1996;37:481–90. .
72. McGlone JJ, Newby BE. Space requirements for finishing pigs in confinement: behavior and performance while group size and space vary. Appl Anim Behav Sci 1994;39:331–8. .
73. Bench CJ, Rioja-Lang FC, Hayne SM, Gonyou HW. Group gestation housing with individual feeding-II: How space allowance, group size and composition, and flooring affect sow welfare. Livest Sci 2013;152:218–27. .
74. Taylor IA, Barnett JL, Cronin GM. Optimum group size for pigs. In : Bottcher RW, Hoff SJ, eds. Livestock Environment V, (2 Proc. 5th. Int. Symp. Am. Soc. Agri. Eng. St Joseph, MI, USA; 1997; p. 965–71.
75. Spoolder HAM, Geudeke MJ, van der Peet-Schwering CMC, Soede NM. Group housing of sows in early pregnancy: a review of success and risk factors. Livest Sci 2009;125:1–14. .
76. Rodenburg B, Koene P. The impact of group size on damaging behaviours, aggression, fear and stress in farm animals. Appl Anim Behav Sci 2007;103:205–14. .
77. Anil SS, Anil L, Deen J, Baidoo SK, Walker RD. Factors associated with claw lesions in gestating sows. J Swine Health Prod 2007;15:78–83.
78. Marchant-Forde JN. Welfare of dry sows. In : Marchant-Forde JN, ed. The welfare of pigs New York, USA: Springer; 2009. p. 95–139.
79. Spoolder HAM, Burbidge JA, Edwards SA, Lawrence AB, Simmins PH. Effects of food level on performance and behaviour of sows in a dynamic group housing system with electronic feeding. Anim Sci 1997;65:473–82. .
80. Li YZ, Gonyou HW. Comparison of management options for sows kept in pens with electronic feeding stations. Can J Anim Sci 2013;93:445–52. .
81. Van der Mheen H, Spoolder HAM, Kiezebrink MC. Stable versus dynamic group housing systems for pregnant sows and the moment of introduction. In : Proc. 37th. Int. Cong. Appl. Etho; 2003 June 24–28; Albano, Terme, Italy; 2003. 90. .
82. Anil L, Anil SS, Deen J, Baidoo SK, Walker RD. Effect of group size and structure on the welfare and performance of pregnant sows in pens with electronic sow feeders. Can J Vet Res 2006;70:128–36.
83. Strawford ML, Li YZ, Gonyou HW. The effect of management strategies and parity on the behaviour and physiology of gestating sows housed in an electronic sow feeding system. Can J Anim Sci 2008;88:559–67. .
84. Meunier-Salaün MC, Edwards SA, Robert S. Effect of dietary fibre on the behaviour and health of the restricted fed sow. Anim Feed Sci Technol 2001;90:53–69. .
85. Verdon M, Hansen CF, Rault JL, et al. Effects of group housing on sow welfare: a review. J Anim Sci 2015;93:1999–2017. .
86. Spoolder HAM, Burbidge JA, Edwards SA, Simmins PH, Lawrence AB. Provision of straw as a foraging substrate reduces the development of excessive chain and bar manipulation in food restricted sows. Appl Anim Behav Sci 1995;43:249–62. .
87. Bergeron R, Gonyou HW. Effects of increasing energy intake and foraging behaviours on the development of stereotypies in pregnant sows. Appl Anim Behav Sci 1997;53:259–70. .
88. Bench CJ, Rioja-Lang FC, Hayne SM, Gonyou HW. Group gestation housing with individual feeding—I: How feeding regime, resource allocation, and genetic factors affect sow welfare. Livest Sci 2013;152:208–17. .
89. Brouns F, Edwards SA. Social rank and feeding behaviour of group-housed sows fed competitively or ad libitum. Appl Anim Behav Sci 1994;39:225–35. .
90. Barnett JL. Measuring pain in animals. Aust Vet J 1997;75:878–9. .
91. Andersen IL, Bøe KE, Kristiansen AL. The influence of different feeding arrangements and food type on competition at feeding in pregnant sows. Appl Anim Behav Sci 1999;65:91–104. .
92. Olsson A-Ch, Andersson M, Botermans J, Rantzer D, Svendsen J. Animal interaction and response to electronic sow feeding (ESF) in 3 different herds and effects of function settings to increase capacity. Livest Sci 2011;137:268–72. .
93. Arey DS. The effect of bedding on the behaviour and welfare of pigs. Anim Welf 1993;2:235–46.
94. Jang JC, Hong JS, Jin SS, Kim YY. Comparing gestating sows housing between electronic sow feeding system and a conventional stall over three consecutive parities. Livest Sci 2017;199:37–45. .
95. Bruce JM, Clark JJ. Models of heat production and critical temperature for growing pigs. Anim Sci 1979;28:353–69. .
96. Tuyttens FAM. The importance of straw for pig and cattle welfare: a review. Appl Anim Behav Sci 2005;92:261–82. .

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Figure 1

Diurnal changes in plasma cortisol of gestating sows fitted with an indwelling jugular catheter. The meal-induced release of cortisol is clearly visible [32].

Table 1

The five freedoms as the fundamental experience goals for animals

Freedom How
1. Freedom from hunger and thirst By ready access to fresh water and a diet to maintain full health and behavior.
2. Freedom from discomfort By providing an appropriate environment including shelter and a comfortable resting area.
3. Freedom from pain, injury, or disease By prevention or rapid diagnosis and treatment
4. Freedom to express normal behavior By providing sufficient space, proper facilities, and a company of the animal’s own kind. Also: Possibility to carry out natural behaviors.
5. Freedom from fear and distress By ensuring conditions and treatment which avoid mental suffering.

Farm Animal Welfare Council [13].