Group gestation housing with individual feeding—I: How feeding regime, resource allocation, and genetic factors affect sow welfare

Livestock Science 152 (2013) 208–217

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Livestock Science journal homepage: www.elsevier.com/locate/livsci

Review article

Group gestation housing with individual feeding—I: How feeding regime, resource allocation, and genetic factors affect sow welfare C.J. Bench a,n, F.C. Rioja-Lang b, S.M. Hayne b, H.W. Gonyou b,c a b c

Department of Agricultural, 3-18A Ag/Forestry Centre, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2V8 Prairie Swine Centre, Inc. Floral, Saskatchewan, Canada S7H 5N9 Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5A8

a r t i c l e in f o

abstract

Article history: Received 8 March 2012 Received in revised form 21 December 2012 Accepted 26 December 2012

As group gestation housing replaces the use of sow stalls, research consensus on how to best manage welfare challenges associated with group systems is needed and valued by industry and policymakers. At present, there is a lack of welfare research directly comparing different group sow housing systems which incorporate individual feeding methods. The aim of this review was to assess current research findings and highlight further areas of research required to provide producers with information about which individual feeding methods best promote sow welfare and productivity in group systems. Regardless of feeder type, feed restriction during gestation is associated with hunger-motivated stereotypic activity, increased aggression, and feeding competition within group sow housing. Further, some systems, such as ESFs which provide sows with a high degree of protection while eating, present unique challenges by requiring sows to eat sequentially rather than simultaneously as a group. Bulking diets with fibre effectively alleviates many hunger-motivated behaviour and welfare concerns. However, dietary fibre also increases feeding time which can cause crowding of sequential feeding systems, thereby reducing feeder capacity. Artificial selection against aggression and aberrant behaviours and the tailoring of genotypes to specific feeding systems as a means of increasing sow welfare is largely unstudied in the scientific literature and presents a valuable area for future sow research. & 2013 Elsevier B.V. All rights reserved.

Keywords: Gestation sows Group housing Individual feeding Genetics Welfare Resource allocation

Contents 1. 2. 3.

n

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of individual feeding systems for group housed sows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors affecting the welfare of individually fed group housed sows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Feeding regime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1. Restricted feeding practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2. Diet formulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3. Diet supplements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.4. Feeding schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.5. Feeding regime key messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Corresponding author. Tel.: þ 1 780 492 9081; fax: þ1 780 492 4265. E-mail address: [email protected] (C.J. Bench).

1871-1413/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.livsci.2012.12.021

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3.2.

4.

Feed/water resource allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Feeder area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2. Direct comparisons of feeder types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3. Resource allocation key messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Sow genetics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1. Sow genetics key messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conflict of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction In the developed world, many swine producers are converting to group housing for sows either voluntarily or under legislation. To date, several states in the United States have imposed bans on sow gestation stalls as a result of successful ballot initiatives and in reaction to public concern, including: Florida, Maine, Arizona, Oregon, California, Colorado, Michigan, and Ohio. Gestation stalls were banned in the United Kingdom in 1999, with the rest of the European Union restricting use from 4 weeks after service until 1 week before the expected time of farrowing from 2013 (Council Directive 2001/88/EC, 2001). Whether driven by corporate competitiveness or government legislation, the intent of the move towards group housing for sows has been to improve sow welfare by allowing greater freedom of movement during gestation. However, due to feed restriction in gestation, intersow aggression remains a major welfare concern in group housing which, in turn, affects many other aspects of sow welfare (Marchant et al., 1995). Further complicating the transition to group housing is the number of feeding methods available to allocate feed to restricted gestating sows. Within group systems, sows may be fed collectively (either on the floor or in troughs) or individually (e.g. electronic sow feeder (ESF), free stalls, Fitmix, or walk-in lock-in stalls; Fig. 1). Individual feeding

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typically denotes that individual sows are ‘‘protected’’ from other sows while eating, which is not the case with floor, trough, short feeding stalls (partial stalls) or Fitmix feeding (despite being a type of non-stall, unprotected ESF). Even in the case of trickle feeding systems (Hulbert and McGlone, 2006), partial stalls may be utilised in an attempt to reduce competitiveness and aggression during feeding. However, such systems would not be considered truly protective due to the variation in the length of barriers and other design attributes. For this review, individual feeding is simply defined as the attempt to feed sows individually (i.e. provide some control over feeding and does not include feeding on the floor) whether the system is protected or not (i.e. with at least a partial barrier). With regard to sow welfare, whether an individual feeding method provides protection during feed consumption will naturally impact levels of sow aggression and competition in a group sow environment. As the industry moves towards group housing of sows, individual feeders are the most likely systems to be utilised. For this reason, the objective of this review is not to compare the use of gestation stalls versus group housing, but to take an in-depth look at group sow housing systems which specifically utilise some form of individual feeding (protected and unprotected; sequential and simultaneous), and to identify gaps in the current research literature in order to shed light on what is known

Fig. 1. Group gestation sow housing system using walk-in lock-in style individual feeding system which provides for simultaneous, protected feeding. Photo courtesy of Dr. Fiona Rioja-Lang, Prairie Swine Centre, Canada.

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and still left to be discovered about these housing systems. Previous reviews regarding group-housed sows have focused on early pregnancy, with some discussion on feeding systems and/or reproductive success (e.g. Spoolder et al., 2009). Due to the various factors which contribute to a sow’s overall well-being, the current review specifically focuses on three key aspects of group gestation sow housing: feeding regimes, resource allocation, and sow genetics. Space allowance, group size and composition, and flooring aspects are covered in a companion comprehensive review regarding the welfare of individually-fed, group-housed gestating sows (Bench et al., in press). 2. Comparison of individual feeding systems for group housed sows A scientific literature search was conducted and resulted in almost 400 research abstracts identified on the topic of group housing of gestating sows involving individual feeding systems. Of these identified abstracts, 225 research articles were chosen based on the variables measured in the research (e.g. feeding regime, resource allocation, and sow genetics) as well as factors affected (e.g. production performance, overall well-being, and lifetime productivity). The three main databases that were used included AGRICOLA (USDA, indexes 2500 journals since 1970), CAB International (indexes over 9000 journals, books and conference proceedings), and Scopus (indexes over 16,000 peer-reviewed journals, and numerous conference proceedings and books). As a measure of overall sow welfare in group sow housing systems which utilise one or more types of individual feeding method, the current review used a variety of outcome measures including: behaviour (i.e., aggression, responses to behavioural tests, general behavioural time budgets, stereotypies), injuries (i.e., scratches, lesions, vulva bites, lameness), physiology (i.e., cortisol concentration, heart rate, muscle/bone strength) and productivity (i.e., fertility, litter size, litter weight, piglets/sow/year, and body condition). These parameters are validated as welfare measures in the existing scientific literature and based on the Five Freedoms (Webster, 2001), which include freedom from: (1) hunger, thirst and malnutrition, (2) thermal and physical discomfort, (3) injury or disease, (4) suppression of normal behaviour, and (5) fear and distress. 3. Factors affecting the welfare of individually fed group housed sows 3.1. Feeding regime For the sake of this review, feeding regime includes data available on diet formulations (e.g. effect of increased fibre in the diet), feeding schedule, and feeding order. It is important to note, that regardless of the feeding method, all gestating sows are feed restricted as a means of reducing reproductive problems. Furthermore, straw has been studied in the scientific literature as a feed supplement (i.e. bulking agent or straw racks),

environmental enrichment (e.g. straw racks), and as a flooring substrate. As such, discussions regarding straw are found throughout the review depending on the capacity within which straw was investigated. 3.1.1. Restricted feeding practices In many research findings, feed restriction, and not physical restraint (i.e. confinement), has been found to be a major contributor to increased activity levels and higher incidences of drinking and chain manipulation in sows fed with individual stalls (Terlouw et al., 1991). Furthermore, such activities do not seem to replace or alleviate the need for post-feeding nosing and rooting of substrates. Petherick and Blackshaw (1989) investigated the effects of three feeding regimes (restricted ration, ad libitum, and restricted ration þsupplemental straw) on sow reproductive performance (in groups of 4 sows over three consecutive gestations) using partial barriers on all feed stalls. Sows fed ad libitum ate approximately three times the amount of feed that was allocated to them on restricted ration and supplemental straw, suggesting that feed restricted sows will eat more if provided the opportunity. However, feeding regime was not found to affect any reproductive performance measures (i.e. numbers of piglets live born, stillborn, weaned, birth or weaning weights) when the partial feeding stalls were used. The authors found it probable that no adverse effects of the feeding regimes were found due to the short time (13 days) of each treatment and because multiparous animals were used in the study. These results suggest that the welfare of ration-fed sows, whose appetite is not satiated, may be improved without a loss in sow productivity when fibrous feedstuffs are provided using partial feed barriers. While conventional restricted feeding practices during gestation help to maximise economic performance (Meunier¨ et al., 2001), sows often exhibit hunger-motivated Salaun stereotypic activity, increased aggression, and feeding competition in group housing systems. As such, individual feeding helps to alleviate aggression amongst sow groups related to competition over limited feed resources. Due to a combination of feeling hungry and social competitiveness, feed restricted sows have been found to exhibit higher basal cortisol levels and rectal temperatures ¨ et al., 2001) indicating elevated levels (Meunier-Salaun of perceived stress. Unmitigated, this stress may lead to smaller litter sizes and decreased pregnancy rates (Kongsted, 2005), thereby effecting sow productivity. Spoolder et al. (1997) investigated the effects of food level (restricted vs. ad libitum) on performance, aggression, and skin damage in combination with a deep-straw system. Feed restricted sows exhibited more activity and showed more straw manipulation compared with ad libitum sows. While Spoolder et al.’s (1997) findings echo previous findings (Terlouw et al., 1991) that feed restriction is a leading cause of sow activity, the study results also found effective ways to redirect hunger-motivated behaviours while not compromising sow performance. However, Spoolder et al. (1997) found no difference in aggression or skin damage between feeding regimes. Thus, the authors concluded that within a deep-straw system, aggression may not always be influenced by

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feeding level. In addition, the incidence of stereotypies, inactivity, self-directed behaviour, and substrate-directed behaviour in stall-fed sows is a useful indicator of satiety as part of overall sow welfare assessment (Zonderland et al., 2004). 3.1.2. Diet formulation Diet formulation includes the use of high energy ingredients, feedstuffs and moisture that provide bulk to the diet in order to influence hunger motivation and sow behaviour. The effects of diet formulation (e.g. low vs. high fibre or using ingredients such as sugar beet pulp) and feeding level during gestation was investigated for effects on behaviour patterns in group housed gilts fed in individual feeding stalls (Brouns et al., 1994). Gilts fed a high fibre diet took longer to consume their daily feed, were less active, and engaged in less oral behaviours. In a ¨ et al. (2001) found that later study, Meunier-Salaun adding fibre to the gestating sow diet to increase bulk (and satiety) resulted in doubled eating times as well as a 20% reduction in feeding rate, a 30% reduction in operant response in feed motivation tests, and a 7–50% reduction in stereotypic behaviour. Thus, providing dietary fibre effectively reduced some of the key behavioural concerns associated with feed restriction. However, while increased feeding times have been shown to reduce sow hunger, the practice can also crowd sequential feeding systems such as protected ESF, thereby reducing overall feeder capacity within a sow group. When provided with a low-energy conventional diet formulation, individually-fed sows exhibit a slightly higher incidence of skin lesions than those on a highfibre diet (Martin and Edwards, 1994). These results further highlight the importance of roughage in the sow diet as a means of reducing injuries due to aggression within a group housing system. A study by Gjein and Larssen (1995) similarly found that sows in loose herds with an ESF not fed additional roughage had 1.7 times greater risk of body lesions than sows in commercial herds that used additional roughage feeding. In fact, the relative risk of vulva biting was 2.6 times higher in loose herds with no roughage feeding as compared with loose herds with adequate feeding of roughage. In addition to dietary fibre, Gjein and Larssen (1995) also found that gate design on an ESF influences the incidence of vulva biting. Sows in loose herds with an ESF feeding station with a mechanical hind gate had 1.8 times greater risk of vulva lesions than sows in loose herds that used a feeding station with an electronic gate. In the earlier mentioned Brouns et al. (1994) study, the incidence of aberrant oral behaviours was minimised when a fibrous diet sourced from sugar beet pulp was offered ad libitum. Thus, showing that fibre for the sow diet can come from a variety of sources and have welfare benefits. van der PeetSchering et al. (2003) studied the effect of a starch diet or a diet with a high level of fermentable non-starch polysaccharide (fNSP) feed using individual stalls during gestation over the first two parities on the development of stereotypic behaviour. High fNSP-fed sows reduced the frequency of total non-feeding oral activities in gestating sows. Later studies also investigating fNSP-rich diets

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(sugar beet pulp) found similar reductions in stereotypic sow behaviour (de Leeuw et al., 2004, 2005). Using an ESF system, Ru and Bao (2004) also found that feeding high fibre diets to dry sows enables sows to be fed ad libitum rather than in a restricted manner. However, the effect of dietary fibre on feed intake and nutrient utilisation is dependent on the quality of fibre sources. Most research has focused on sugar beet pulp, straw, lucerne meal and by-products. Through the course of this review, the need was identified for future research to evaluate widely available and cheap fibre materials and feed grains for developing the best strategy to control nutrient intake of dry sows while feeding ad libitum. Furthermore, the authors were unable to find scientific literature which specifically investigated the effect of liquid versus dry feed on the welfare of group-housed sows which provided direct comparisons between individual feeding methods.

3.1.3. Diet supplements In addition to diet formulations, dietary supplements have also been used in conjunction with individual feeding systems as a means of providing greater gut-fill and satiation to feed restricted sows. Some of this research has investigated the use of straw racks to provide fibre supplemental to the sow diet. The actual degree to which supplemental fibre compensates for a lack of dietary fibre has not been determined with regard to sow welfare. In group housing systems with free access stalls, Spoolder et al. (1995, 1996) evaluated activity levels in both ad libitum and restricted-fed sows with and without access to supplemental straw. Activity levels were found to be the highest immediately after feeding, with restricted-fed sows more active than ad libitum sows. Most activity in the post-feed period was directed toward substrates. In restricted-fed ‘‘no straw’’ sows, most behaviour was directed towards chains and bars, resulting in levels 3 to 4 times higher than in other treatment groups. Restrictedfed straw sows directed their foraging behaviour mainly towards straw provided in racks. The authors concluded that feed-restricted pregnant sows have abnormally high levels of chain and bar manipulation which can be prevented by providing ‘straw-access’ which acts as a foraging substrate. These findings suggest that when dietary fibre is not a feasible option for producers, access to supplemental fibre sources such as straw has important welfare benefits for the sow. Krause et al. (1997) further studied the provision of supplemental straw placed in ‘‘feeding racks’’ and feeder types by comparing four treatments: (1) ESF for sequential feeding of sows with straw rack (ESF with straw), or not (ESF without straw), and electronically-controlled simultaneous feeding in boxes (FB) and with straw available (FB with straw) or no straw in the feeding rack (FB without straw). Krause et al. (1997) concluded that the sequential feeding of group housed ESF-fed sows contributes toward the development of serious behavioural problems (e.g. agonistic interactions resulting in injury) among sows. Sows in the study were most active in FB with straw and least active in ESF without straw. Thus, some types of individual

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feeding may be better suited to the provision of supplemental fibre compared with others. Some studies have investigated the welfare implications of supplemental fibre provided pre- versus postfeeding. For example, large, dynamic groups of ESF sows provided with access to barley straw in racks (placed preand post-feeding exercise areas) was investigated by Stewart et al. (2008). The results found an average 6% of sows visited each rack during the morning hours (08:00– 12:00). On average, more sows spent time at the postrather than pre-feeding racks provided during a 24 h period. In addition, sows provided straw spent significantly less time exploring the floor as a result of providing an outlet for exploratory and unsatisfied foraging behaviour. While average sham chewing levels did not differ between treatments, sows exhibited most sham chewing post-feeding. However, use of straw did not affect the incidence of sham chewing. As such, the authors concluded that the welfare benefits associated with barley straw racks is limited. In contrast, when ESF-fed sows were provided with grass silage racks as opposed to straw racks, O’Connell (2007) found that on average 78.5% of sows observed using the grass silage racks were newlyintroduced animals in a large, dynamic group. Furthermore, sham chewing behaviour was reduced through the provision of grass silage racks. This is in conflict to Stewart et al. (2008) which found no difference in sham chewing between sows provided with barley straw racks and those without racks. Further investigation is required to determine if grass silage is more effective at reducing sham chewing compared with barley straw within ESF feeding systems. As a whole, the utility and effectiveness of supplemental straw and bulked diet formulations may be significantly impacted by the individual feeding system used. Also, depending on time since introduction (newly introduced vs. later), as well as how supplemental straw is presented, behavioural benefits can be achieved which have implications for sow welfare. For example, aggression was found to be a problem as a result of increased activity levels associated with the straw racks, but decreased activity around the ESF feeding station (Kroneman et al., 1993a, 1993b). In these studies, sows exhibited a strong preference for taking straw from a rack compared with straw from the floor in the lying area. As a result, the provision of straw racks increased the number of aggressive interactions among sows, and led animals away from the waiting and feeding station areas. 3.1.4. Feeding schedule Feeding schedule specifically refers to a 24 h cycle used in conjunction with individual feeding methods, particularly those that result in sows feeding in series rather than simultaneously (e.g. ESF stations). In the Netherlands, early experience with group sow housing which utilised ESF feeding was not entirely satisfactory. This was primarily because vulva biting and hoof lesions were the predominant health problems in the system (Kroneman et al., 1993a, 1993b). When feeding stations were re-designed with separate entrances and exits (e.g. walk through stations with side and front exits, instead of back-out exit stations), the incidence of vulva biting

decreased (largely due to the decrease of sows queuing to enter the feed station). This may have been influenced by the fact that, by nature, pigs eat in social groups rather than individually or sequentially. Rizvi et al. (1998) found when grouped sows were ESF fed once a day with ad libitum access to water, the number of sows per drinker correlated with vulva biting, tail biting, and an increased percentage of cull sows. These findings support recent work by Zurbrigg and Blackwell (2006) who observed once daily feeding using an ESF in a dynamic system led to a higher incidence of vulva lesions and welfare concerns compared to other automatic feeding methods and manual feeding. In a recent study, Olsson et al. (2011) reported that more than 50% of sow visits to ESF feeders are non-nutritional in nature, with approximately 33% of sow visits resulting in sows biting one another while entering the feeding system. On average, 4–6 sows often queue at the ESF entrance gate, despite one-third of queued sows having previously eaten (Olsson et al., 2011). Feeders set to shorten feeding time per sow (thus increasing feeder capacity), resulted in more sow queuing. Furthermore, herds with greater feeder capacities (shortest feeding times), had the highest incidence of vulva biting and feed wastage. As such, the authors concluded that sow behaviour is heavily influenced by feeder settings. In addition to queuing and vulva biting, feeding schedule can also impact the feeding order of sows. It should be noted that deviations in feeding order in ESF systems may indicate disease, oestrus, reproductive and/or other problems (Bressers et al., 1993.) Sows in protected ESF systems adapt to a daily feeding schedule and routine by establishing a relatively stable feeding order which is determined by social rank (Csermely, 1989; Hunter et al., 1988), duration of stay in the system, experience with the feeding station gained in earlier pregnancies and parity (Lembeck et al., 1996). Changing feeding start from daytime to nighttime is often accompanied by reduced ESF feeder occupation in the period following start of the feeding cycle (Jensen et al., 2000). Even in non-protected ESF, such as Fitmix, feeding order tends to be relatively stable, is quickly established and maintained (Chapinal et al., 2008). High ranking sows fed earlier and made the same number, but longer, visits compared with lowranking sows. Thus, higher ranking sows occupied the feeder for longer periods of time every day. As such, in medium-size (e.g. groups of 20 sows each), stable groups of sows, Fitmix seems to be an efficient feeding system. In ESF systems with a forward exit from the feed station, the results have shown increased station visits daily, but non-feeding visits tend to be of shorter duration so that total occupation time is similar (Edwards et al., 1988). In some cases, sows learn to circumvent the computercontrolled mechanism locking the rear gates and may show aggression towards other animals in the station. As such, a forward exit station with positive closing of the rear gate is desirable, but some problems with station design remain to be solved. Another alternative method which was designed to reduce aggression is simultaneous trickle feeding (which aims to reduce competition by feeding sows all at the

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same time, but is not considered a ‘protected’ feeding system). Chapinal et al. (2010) investigated the effect of trickle feeding versus an unprotected (i.e. competitive system which does not include a feeding stall) electronic sow feeding (Fitmix) and found aggression increased when the unprotected system was utilised in grouped sows. The authors concluded that sequential feeding associated with unprotected feeding caused the system to be more competitive in nature, thus resulting in more aggressive encounters and sow injuries. These results agree with earlier work by Turner et al. (2000) which found that high levels of competitive aggression can be induced due to limited resources such as water, feed and space. Limitations to resources can be due to restrictions on quantity, temporal access, or distribution. When aggression occurs, subordinates within the group tend to experience compromised welfare (Csermely and WoodGush, 1990). 3.1.5. Feeding regime key messages Welfare concerns due to feed restriction are not alleviated by either group housing or individual feeding methods. It is well-documented that restricted feeding in group housed sows leads to increased hunger and frustration, which subsequently leads to increased stereotypic and aggressive behaviours, increased incidence of skin and hoof lesions, vulva biting and cull sows. The benefit of individual feeding systems is that they allow each sow some degree of protection from aggression while feeding. However, hunger-motivated behavioural concerns and aggression in common areas remain welfare and productivity concerns within group systems that utilise any type of individual feeder. As such, the incidence of stereotypies, inactivity, self-directed behaviour, and substratedirected behaviour, which are indicative of satiety, should be included in any sow welfare assessment model. Bulking diets with fibre effectively alleviates several behavioural concerns due to feed restriction. Several dietary fibre sources have been studied, but the effect on feed intake and nutrient utilisation is dependent on the quality of the fibre sources. As such, this review has identified the need for future research in this area. Furthermore, while dietary fibre increases feeding times, it can also crowd sequential feeding systems such as protected ESF, thereby reducing feeder capacity. As a result, the provision of supplemental fibre, particularly post-feeder, has been investigated and determined to have important welfare benefits for sows. However, some sources of supplemental fibre may prove more effective than others and should be investigated further. Individual feeding systems which require sows to feed sequentially (e.g. ESF) should not be used in conjunction with supplemental fibre sources unless aggression and injury related to competition for access to the supplemental source can be prevented. With regard to feeding schedules, individual feeders that require sows to feed in series rather than simultaneously often cause increased vulva biting due to queuing of hungry sows. Thus, sow behaviour is heavily influenced by feeder settings. Feeder schedule and feeder type also influences feeder order, with more dominant sows

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feeding first. As such, sequential systems that allow for protected feeding and a forward exit with positive closing of the rear gate has been identified as important design components. 3.2. Feed/water resource allocation Feed and water resource allocation includes those studies which have focused on feeder area design in combination with feeder type. For example, where feeders are located in a pen, space around the feeder, gated versus non-gated design features, and the amount of protection provided during feeding. Feeder types and amount of protection offered during feeding are compared throughout this review, however special emphasis is placed on it within this section. 3.2.1. Feeder area The design of the feeding area in any group housing system is extremely important, as it affects how sows behave and interact with one another. Leeb et al. (2001) studied the effect of group size, design of the feeding area, and area per sow and found all had a significant influence on the extent of sow injuries. Smooth lying surfaces around feeders and the opportunity for sows to move around within the group system reduced the incidence of callosites. The authors concluded that skin lesion patterns in sows can be used as a good indicator of welfare and effectiveness of feeder area provisions. Durrell et al. (1997) found that providing spent mushroom compost in suspended racks in the area of stall feeders also reduced aggression and injuries. It is important to note that the authors considered the compost racks to be enrichment rather than part of a feeding regime strategy. Relatively little research has been conducted on the impact of the design of the feeding area and resource allocation in individual feeding systems within group housing on sow productivity. Spoolder et al. (1996) studied sows in loose housed groups of 6 with individual free access feeding stalls and found that significantly more ‘‘no-straw’’ sows failed to start the second parity compared with sows provided with supplemental straw. In a study using drop-fed vs. trickle fed individual feeding stalls, Hulbert and McGlone (2006) found that productivity measures did not differ among feeder treatments. However, in simultaneous drop-fed feeding systems, sows were found to have greater phagocytosis compared with trickle-fed sows. It is important to note that non-gated feeding stalls are used for drop and trickle feeding, which makes these systems an overlap between individual and non-individual feeding as sows can be displaced from a non-gated stall. As a result, aggression often occurs during feeding periods. While feeder treatment did not influence sow productivity, drop-feeding seemed to affect sow immune function, which could have been due to the level of displacement as a result of feeder design. However, a review of the scientific literature was unable to identify specific research regarding how feeder type or design of the feeding area affects the sow immune system apart from how housing effects stress cortisol levels and the incidence of stereotypies (Pol et al., 2002).

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3.2.2. Direct comparisons of feeder types Throughout the review of the scientific literature, it was possible to conduct a small number of direct comparisons of individual feeder types. For example, Broom et al. (1995) studied two group sow housing systems with individual feeding (one with feeding stalls, the other with ESF) which were compared with gestation stalls. When the two group sow housing systems were compared, sows fed with an ESF exhibited more fighting, especially immediately after mixing, but fewer total agonistic interactions compared with sows in groups of 5 during the first pregnancy. Oral stereotypies were slightly higher in small groups, compared with larger groups. These results may have been confounded by pen space allowance for the smaller groups since groups of pigs tend to cluster within large spaces as part of their species-typical thigmotaxic behaviour. By the fourth pregnancy, few differences in aberrant behaviour between sows in small and large groups were observed. The authors concluded that all sows seemed to have adapted well to the housing and feeder system. In comparison, sows provided with partial stalls have been found to exhibit fewer aggressive interactions around feeding (Barnett et al., 1996). These findings support previous physiological data obtained by the same research group in which pregnant sows provided with partial feeding stalls had lower average daytime cortisol concentrations once social relationships in the group had stabilized (Barnett et al., 1992). However, this type of stabilisation effect can take anywhere from 10 days to 4 weeks to achieve. On the basis of the cortisol data, both studies (Barnett et al., 1992, 1996) suggest a welfare benefit to the provision of partial feeding stalls. It is important to note that activity levels were highest just after feeding in free access stalls which had frontmounted chain loops as part of the feeder design. Furthermore, during the post-feeding period, activity toward substrates in the pen would be expected (Spoolder et al., 1995). When comparing ESF and trickle feeding with free access stalls, Backus et al. (1997) observed a higher percentage of gait disorders, claw lesions, and skin scratches. Similarly, a Zurbrigg and Blackwell (2006) survey found that ESF-fed sows show a higher incidence of lameness compared to other systems. However, the results may have been biased as the study included a farm which had ESF mechanical problems. Thus, the increased lameness observed in some of the study’s ESF sows may have been due to an unconnected malfunction rather than the system itself. The same survey found that pigs in ESF dynamic systems were dirtier than other group sow systems. In this case, sow dirtiness was used as an indicator of lameness since lame sows tend to lay more and are therefore more likely to be dirty. Hulbert and McGlone (2006) found that scratch scores did not differ among feeding stall treatments. However, earlier studies found that ESF are associated with greater vulva biting, tail biting, and an increased percentage of cull sows (Rizvi et al., 1998). Specifically, the survey study by Rizvi et al. (1998) reported vulva biting incidences as high as 70% of farms. In contrast, Scott et al. (2009) found that 21% of ESF-fed sows had a score of 1 or more for skin

lesions, which the authors attributed to sows lining up to enter the ESF and biting the sow in front to dislodge her from the feeder. Scott et al. (2009) further suggest that any group sow housing that utilises individual feeding can be expected to have higher levels of vulva biting. These results agree with the findings of previously discussed studies by Chapinal et al. (2010) and Turner et al. (2000) that expressed concern for sows fed in systems requiring animals to feed in series rather than simultaneously. Kongsted et al. (2007) monitored indicators of feed intake, fear of humans, and social behaviour in group housed sows in 14 herds, which utilised both ESF and individual feeding stalls. Within the different individual feeding systems, first parity sows exhibited significantly more skin scratches than older sows in herds with no escape possibilities (e.g. small group sizes with no protected feeding stalls). These findings may explain why Chapinal et al. (2008) found subordinate sows and gilts feed later in the feeding order as a result of experiencing displacement at the feeder. These studies indicate that within individual feeding systems, subordinate gilts and sows can experience aggression and dislodging from the feeder which results in welfare concerns (Csermely and Wood-Gush, 1990). 3.2.3. Resource allocation key messages Feed station design is a very important determinant of behaviour, and subsequent resource allocation, in group sow housing systems. Group size, design of feeding area, and area per sow all has a significant influence on the incidence of sow injuries. Smooth lying surfaces around feeders and opportunities for sows to move around within the group system were found to reduce sow injuries the greatest. Generally, most studies have focused on aggression and injuries associated with ESF systems (e.g. lameness, vulva biting, tail biting, and agonistic interactions resulting in injuries). The use of supplemental straw either pre/post-feeding station has been investigated, however the literature does not reach a conclusion on the optimum practice. While little research has been conducted on the effect of feeder area design on sow productivity, the research that does exist concludes there is little effect. However, drop feeding was found to influence sow immune function which may have been due to increased displacement during feeding. Future research is required to determine whether feeder design and surrounding resources influence sow immune function in addition to perceived stress and sow injury. When comparing different feeder types, sows housed with partial stalls were found to exhibit fewer aggressive interactions around feeding. If non-gated feeding stalls are used as part of group sow housing, the extent of stall protection (i.e. gated vs. non-gated) affects aggression, sow displacement at the feeder, and more. For example, on the basis of cortisol data, it is suggested that partial feeding stalls will provide welfare benefits. However, even with individual feeding systems, subordinate gilts and sows will generally experience aggression, resulting in welfare concerns. Overall, more research is required with regard to the effect of individual feeding systems on sow productivity measures, including

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considerations for dominance hierarchy formation in grouped sows. 3.3. Sow genetics By estimating the heritability of factors such as sow aggression it may be possible to genetically select for the strength or elimination of specific behavioural and welfare concerns. Based on their review of the impact of group size on damaging behaviours, aggression, fear and stress in animals, Rodenburg and Koene (2007) suggested that genetic selection against aberrant behaviour seems promising. For example, Bench (2005) found breed differences in belly nosing and belly sucking in early weaned nursery pigs. Breuer et al. (2003) found breed differences in tail biting behaviour among grow/finish pigs, which was also found to be negatively correlated with leanness (Breuer et al., 2005). In a study designed to estimate the genetic variation in aggressive behaviour of sows at mixing and movement into group housing, as well as maternal ability, Lovendahl et al. (2005) calculated heritability for performed aggression traits and found it to be intermediate (h2 ¼ 0.17 and 0.24), but lower for received aggression (h2 ¼0.06 and 0.04). Heritability of maternal behaviour was also low (h2 ¼0.08). The authors conceded that while the standard errors for the estimates of genetic correlation were large, they indicate that less aggressive sows are stronger-responding mothers (rg ¼  0.3). The authors concluded that performed aggression in sows is a heritable trait, and selection against aggression is possible without off-setting maternal behaviour. However, specific studies on the genetic correlation of injuries to group housed sows (e.g. lameness or lesions) which are individually fed, were found to be lacking in the current scientific literature. Selection against stereotypic behaviour has also been considered. Stereotypies observed in the post-feeding period for 2 stall-fed genotypes (Large White and Large White  Landrace; Vieuille-Thomas et al., 1995) revealed genotypic differences. In this case, sows were separated by metal bars placed at the feeding trough. However, the genotypes were confounded by housing treatment comparisons (e.g. group-housed stall-fed systems at 2 farms). A reduction in stereotypies was observed when the Large White  Landrace treatment was housed in groups, however it is not known whether the same reduction would have been observed in the Large White only genotype. Despite group housed sows exhibiting the lowest incidence of stereotypies, the incidence in groups was 66% of sows performing stereotypies for this particular study. Breed differences have also been investigated in relation to how the sows physically relate to a group housing system. Marchant and Broom (1996) studied the amount of time taken to lie down and stand up in an ESF group sow housing systems in relation to physical space based on genotype. Specifically, 2 crossbred genotypes were used: (1) Tribred  Landrace and (2) Tribred  Hampshire. Compared with stalled sows, group housed sows took longer to lie down in an open area versus against a wall. There was no genetic difference found in the total time taken for sows to stand up or lie down, however body

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length was significant. ESF-fed sows tended to be longer (1573 mm) than stalled sows (1524 mm) despite being the same age and from the same genetic stock. These results point to the importance of genetics and factors affecting lying down and standing (e.g. body length, weight and conformation) being considered when designing sow housing as it may affect sow welfare. In stall-fed sows, Dailey and McGlone (1997) found few significant genotype and genotype by environment interactions in a study using pregnant gilts of PIC Camborough-15, PIC Camborough-Blue and York  Landrace based on overall behaviours observed, which indicated that these particular genotypes generally express similar behaviour. 3.3.1. Sow genetics key messages It has been suggested that genetics may play a role in stereotypy development and general activity (e.g. aggression and overall activity) in group housed sows, and that genetic selection against aberrant behaviour may be a solution. However, comparisons of sow breeds, selected lines, or studies on the genetic correlation of injuries in group housed sows (e.g. lameness or lesions) which are individually fed, are limited and currently lacking in the scientific literature. As such, no conclusion can be drawn at this time with regard to how different sow lines should be best managed in group housing which incorporate individual feeding methods (e.g. aggression in protected vs. non-protected systems). It is considered that feeding competition issues are likely to be more prevalent in some sow lines compared with others and this should be taken into consideration when choosing an individual feeding method. Overall, in terms of sow behavioural traits, non-aggressive sows may be more advantageous for rearing in group housing to avoid feed aggression. Preliminary data suggests that it may be possible to select against aggression in sows without reducing maternal behaviour. As such, future group sow housing should place greater emphasis on sow behavioural genetics. 4. Conclusions As the swine industry transitions away from gestation stalls, group housing which allows barn managers tight control over the feed intake of individual sows are the most likely systems to be utilised by industry. As such, this review has focused on group housing which includes some form of individual feeding method in order to evaluate what is currently reported in the scientific literature regarding the welfare of sows in these types of systems. Regardless of feeder type, feed restriction during gestation is associated with hunger-motivated stereotypic activity, increased aggression, and feeding competition within group sow housing. While individual feeding methods help alleviate some aggression due to sow displacement during meals, it is difficult to eliminate it completely. Further, some systems, such as ESFs which provide sows with a high degree of protection while eating, present unique challenges by requiring sows to eat sequentially rather than simultaneously as a group. As a result, such systems often lead to queuing of hungry sows and increased levels of vulva biting. Higher levels of

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lameness, gait disorders, claw lesions, tail biting, and cull sows within ESF systems have also been noted in some of the scientific literature. One common explanation provided for this is that ESF, by requiring sows to eat one at a time, results in more dominant sows eating first. As a result, smaller and more subordinate sows can experience aggression and dislodging from the feeder which is a welfare concern. Bulking diets with fibre effectively alleviates many hunger-motivated behaviour and welfare concerns. However, dietary fibre also increases feeding time which can cause crowding of sequential feeding systems, thereby reducing feeder capacity. Studies which have used supplementary fibre (e.g. straw provided in racks) have similarly found them to be effective in alleviating some problem behaviours. Although, some studies also reported increased levels of sow aggression related to competition over these same supplemental resources. Artificial selection against aggression and aberrant behaviours and the tailoring of genotypes to specific feeding systems as a means of increasing sow welfare is largely unstudied in the scientific literature and presents a valuable area for future sow research. Conflict of interest There are no conflicts of interests professionally or financially with this manuscript that the co-authors are aware of.

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