University of Minnesota, West Central Research and Outreach Center, Morris, MN, USA Accepted 4 April 2006 Available online 19 May 2006

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1 Applied Animal Behaviour Science 103 (2007) The behaviour, welfare, growth performance and meat quality of pigs housed in a deep-litter, large group housing system compared to a conventional confinement system Rebecca S. Morrison *, Lee J. Johnston, Adrienne M. Hilbrands University of Minnesota, West Central Research and Outreach Center, Morris, MN, USA Accepted 4 April 2006 Available online 19 May 2006 Abstract The behaviour, welfare, growth performance, and meat quality of deep-litter, large group-housed pigs were compared to pigs raised in a conventional housing system. Castrated males were housed from 9 weeks of age in a conventional housing (15 pigs/pen; 1.0 m 2 /pig) or deep-litter, large group housing system (90 pigs/pen; 1.7 m 2 /pig). Behavioural observations and stress physiology measurements were conducted at 9, 17 and 22 weeks of age. The willingness of the pigs to approach a novel object was assessed using a standard novel object test at 22 weeks of age. Pigs in the deep-litter, group housing system spent more time (P < 0.05) standing, locomoting, and interacting with their environment compared with contemporaries housed in the conventional system. At 17 weeks but not at 9 or 22 weeks, pigs in the conventional housing engaged in more (P < 0.05) social interactions than deep-litter housed pigs. Salivary cortisol was higher (P < 0.05) in deep-litter pigs compared to conventional pigs at 9 weeks of age but were similar at 17 and 22 weeks of age. Pigs in the deep-litter, large group system exhibited more exploratory behaviour (P < 0.05) compared to conventionally raised pigs in the novel test. Loins from pigs housed in the deep-litter, large group treatment had lower (P < 0.01) loin ph, more (P < 0.05) purge loss, more glucose in purge (P < 0.05) and were lighter in subjective colour (P < 0.05) than loins from conventionally housed pigs. However, there were no significant differences observed in the objective colour measurements of L *, a * and b *. A trained sensory panel detected no differences in tenderness, juiciness or overall desirability of loins from deep-litter or conventionally housed pigs. In this experiment, housing system modified pig behaviour, * Corresponding author at: QAF Meat Industries Pty Ltd, PO Box 78, Corowa, NSW 2646, Australia. Tel.: ; fax: address: rmorrison@qafmeats.com.au (R.S. Morrison) /$ see front matter # 2006 Elsevier B.V. All rights reserved. doi: /j.applanim

2 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) fearfulness and stress physiology (at 9 weeks of age) but these differences did not negatively impact meat quality. # 2006 Elsevier B.V. All rights reserved. Keywords: Pig-social behaviour; Fearfulness; Deep-litter; Large groups; Meat quality 1. Introduction Deep-litter, large group systems have been developed as an alternative housing system for growing pigs. These systems are cheaper to establish and are perceived as being more welfare friendly for pigs, compared to conventional housing systems. Deep-litter, large group systems offer more pen space per pig (approximately 1 m 2 per pig), larger group sizes (ranging from 150 to 2000 pigs per pen), an enriched environment (an environment which provides an outlet for rooting and foraging in deep bedding), together with the opportunity for increased social interaction among pigs (Morrison et al., 2003a,b). Conventionally, pigs are housed in more confined systems with fully, or partially slatted floors, liquid effluent system, group sizes ranging from 5 to 50 pigs with a floor space allowance of approximately 0.7 m 2 per pig. There is limited scientific literature to verify the perceived welfare benefits of deep-litter, large group systems. Therefore, it is essential to conduct rigorous assessments of welfare, using measures of stress physiology and behaviour, on pigs raised in deep-litter systems compared to conventional housing systems (Barnett et al., 2001). Anecdotal evidence suggests that pigs raised in deep-litter, large group systems are less fearful of humans and novel objects and are easier to handle when transporting. Temperamental characteristics such as fearfulness (Pearce et al., 1989; Jones and Waddington, 1992) and learning ability (Warren et al., 1982) are affected by environmental enrichment. Environmental enrichment may affect the pig s behaviour by increasing the time they interact with their environment, and reducing pen-mate directed behaviour (Beattie et al., 1995a; O Connell and Beattie, 1999). These changes may influence the pigs behavioural and physiological responses when they encounter a novel environment (Klont et al., 2001). There is considerable debate in the scientific literature concerning the concept and measurement of fear. Gray (1987) defined fear as a form of emotional reaction to a stimulus that an animal works to terminate, escape from or avoid. In this experiment, as with those conducted by Hemsworth et al. (1996), we have adopted a functional approach to measuring fear. The approach behaviour of the pig to a challenging situation (a novel object) was measured. Animals raised in barren environments, such as conventional systems, may be more fearful during challenging situations than those housed in an enriched environment such as a deep-litter, large group system. Temperamental characteristics, such as fearfulness, are extremely important when handling pigs, especially at the time of slaughter. Fearfulness prior to slaughter can lead to an acute stress response, which may affect meat quality. Rapid glycogenolysis as a consequence of acute stressors imposed on pigs immediately prior to slaughter will increase muscle temperature, increase lactic acid concentration, and increase rate of muscle ph decline post-slaughter (Moss, 1984; Hambrecht et al., 2005), which in turn can lead to pale, soft and exudative (PSE) pork which consumers avoid (D Souza et al., 1998; Faucitano, 1998). It is difficult to compare housing systems since they are often confounded by factors such as pen space, group size, environment and substrate provision. The scientific literature is deficient in information on the relationships between these factors and pig behaviour in large multi-factorial

3 14 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) experiments. There is a plethora of information provided by singe factor studies which have studied the effects of group size (Randolph et al., 1981; Hsia, 1984; Spicer and Aherne, 1987; Mikesell and Kephart, 1999) and enrichment (Wood-Gush and Vestergaard, 1989a,b; Beattie et al., 1995a, 1996, 2000; Peterson et al., 1995) on pig behaviour and performance, however, small groups of pigs in conventional systems have been used in these studies. There are limited studies in which deep-litter, large group systems have been compared to conventional systems per se. In order to compare the behaviour, welfare and growth performance of pigs in deep-litter, large group systems to their counterparts in conventional systems, it is necessary to conduct controlled experiments where inputs which are unrelated to the system are similar i.e., location, feed and genetics, as shown by Morrison et al. (2003a). Therefore, the aim of this experiment was to compare the behaviour, welfare, growth performance, and meat quality of pigs in a deep-litter, large group housing system compared to a conventional housing system. 2. Materials and methods 2.1. Animals and housing treatment The experimental protocols used in this study were approved by the University of Minnesota Institutional Animal Care and Use Committee. This experiment was conducted at the University of Minnesota s West Central Research and Outreach Center, Morris, Minnesota, USA. The experiment commenced on 9 September 2003 and ended on 22 December The average daily temperatures ranged from a minimum of 22 8C to a maximum of 30 8C. Four hundred and fifty, maternal-line barrows (Genetiporc) were used in this experiment. The pigs in both housing treatments came from a common source in which conventional farrowing crates and nursery were used, and they had the same nutrition, health and management regimen. During their nursery and experimental period all pigs were handled similarly. Pigs were introduced to their respective housing systems at 9 weeks of age and remained there until they reached market weight of about kg, at 22 weeks of age. Pigs in both housing systems received the same commercial diet sequence that was based on corn and soybean meal. Diets were in meal form and pigs had ad libitum access to feed. Pigs were checked at a similar time each day by one stockperson who quietly moved through the pens in both housing treatments and visually inspected all animals Treatments Two housing treatments were studied: deep-litter, large group system and conventional confinement system Deep-litter, large group system Two hoop style buildings which utilized natural ventilation, with walls constructed of wood and a polyvinyl tarp roof were used for this experiment. Each building contained two pens which housed 90 pigs each. Each pen measured 6.1 m wide 24.4 m long and provided 1.7 m 2 of floor space per pig. The pen space included a cement feeding pad which extended 6.09 m from the south end of the building. Each pen was equipped with one round self-feeder (Sioux 1 ) which provided 12 feeding spaces (7.5 pigs per feeding space) and one insulated trough waterer which provided four drinking spaces. Feed was delivered to the selffeeder via an auger and pigs were provided with ad libitum feed. Straw bedding was used for deep-litter and was replenished as required to ensure that there were designated dry lying areas within the pen. The floor base under the straw was graded, compacted clay Conventional confinement system Six pens measuring 4.7 m 3.2 m and housing 15 pigs per pen were used. There was one feeder per pen which provided four feeding spaces (3.8 pigs per feeding space) and two nipple waterers. Feed was provided

4 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) manually, and pigs were provided with ad libitum feed. The concrete pen floor was totally slatted and provided 1.0 m 2 of floor space per pig. The environment was ventilated mechanically. All pens were used for the growth performance data collection. All pens in the deep-litter system and four of six pens in the conventional system were used for behavioural observations, stress physiology, and meat quality measurements. The number of pigs treated for illness or injury and the number of mortalities were recorded. The pigs in both housing treatments were weighed 2 days prior to behavioural observations and saliva collection for stress physiology. This was sufficient time for the pigs to settle down after the handling involved in these procedures Behaviour activity and social behaviour observations and fear response Focal-animal sampling, as described by (Jensen et al., 1986), was used to observe behaviour of pigs in both housing treatments during active periods (i.e. morning and afternoon). Focal pigs were identified randomly at the beginning of the experiment. There were 40 focal pigs per treatment (10 pigs/pen). The same focal pigs were used at each observation session (i.e. at 9, 17 and 22 weeks of age). Focal pigs were identified by a coloured spray marking which was applied two days prior to behavioural observations when the pigs were weighed individually. Behaviour was observed using direct observation by two trained observers. Four pens in each housing treatment were used for behavioural observations. Observation platforms were erected 3 m above the deep-litter pens. Observations in the conventional pens were conducted while the observer stood quietly in the alleyway outside the pen. Every effort was made to minimize distraction of the pigs. Each pen was observed twice during each observation period at 9, 17 and 22 weeks of age. One deep-litter pen and one conventional pen were observed in the morning and afternoon of each day. Every observation day was divided into two 2-h sessions; 2 h in the morning (from 07:30 h) and 2 h in the afternoon (from 14:00 h). During an observation session, each focal pig was selected randomly and observed continuously for 5 min. Frequencies of behaviours were expressed as number of occurrences in 5 min using a bout criterion interval of 3 s(jensen et al., 1986). The ethogram described by Morrison et al. (2003a,b) was used to describe pig behaviours. Postures were recorded as the percentage of observation time spent standing, sitting or lying. The activity and social behaviour were pooled into the following categories; idle, locomotory (walking and trotting), physical pen interactions (nose pen fixtures, nosing concrete and rooting), social tactile interactions (anal nosing, nose-tobody, nose-to-nose, pushing-performed and received), aggressive (biting, levering, and parallel pressingperformed and received). The behavioural responses of pigs to a novel object were assessed in a standard test (Hemsworth et al., 1996) when the pigs were 22 weeks of age. Other open field tests to objectively measure the behaviour of pigs are described by Beattie et al. (1995b) and Anderson et al. (2000). The previously selected focal pigs were tested individually in a rectangular pen measuring 4.8 m 2.4 m. The test pen was a portable unit that was moved between the two housing system sites. The pigs were quietly walked similar distances between their pen environment and the test pen. The same stockperson moved the pigs on all occasions, and the focal pigs experienced similar handling conditions prior to the test. Ten equally sized rectangular areas were drawn on the floor of the test pen, which enabled an assessment of locomotion during the familiarisation period. The pigs were first given a 2-min familiarisation period. After the familiarisation period, a novel object (a large orange safety cone measuring 74 cm high with a base of 36 cm) was placed at the end of the pen by the experimenter. Area A was defined as the radius within 0.5 m of the novel object (including novel object). During the subsequent 3 min, the following observations were recorded: time taken for the pig to approach within 0.5 m of the novel object (Area A); total time spent within Area A; time taken to first interact with the novel object, and total number of interactions the pig made with the novel object Stress physiology saliva collection Stress physiology was assessed by the concentration of cortisol in saliva. Salivary cortisol is in the free, biologically active form and is correlated positively with the concentrations of cortisol in blood plasma

5 16 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) (Parrott et al., 1989). Saliva samples were collected from 60 randomly selected pigs in the deep-litter housing system (15/pen) and 40 randomly selected pigs in the conventional housing system (10/pen) per treatment at 9, 17 and 22 weeks of age. Saliva samples were collected using a Salivette (Sarstedt, Aktiengesellschaft and Co., Numbrecht, Germany). The cotton swab was placed on a stiff wire and the pig was allowed to chew on the swab until it was moistened with saliva (approximately 30 s). Experimenters were cautious that a stress response was not induced by this procedure. If the pig appeared stressed as evidenced by changes in their behaviour or vocalizations, the pig was abandoned and another pig sampled. Our sample collection was completed in less than 2 min, which is critical since when collecting saliva there is a 2-min delay before cortisol is released (Broom and Johnson, 2000). The saliva samples were centrifuged at 2000 rpm for 5 min to extract saliva from the cotton balls. Saliva was frozen at 20 8C until samples were analyzed for porcine serum cortisol (total cortisol). The solid phase cortisol radioimmunoassay (Coat-A- Count TKCO, Diagnostic Products Corporation, Los Angeles, USA) was used to measure cortisol concentrations in saliva. All samples were analyzed in duplicate Growth performance All pigs were weighed individually at 9, 17 and 22 weeks of age, and feed disappearance (calculated by weighing the feed) was recorded for calculation of average daily gain, daily feed intake, and efficiency of gain. The pigs were marketed over a period of 2 weeks to maximize the number of pigs that would achieve target weights of 114 kg. The growth performance data in the current experiment is expressed as performance of all pigs from the beginning of the study from 9 to 22 weeks of age Meat quality Meat quality measurements were conducted by the South Dakota State University, Brookings, Meat Laboratory. The 80 focal pigs (40 per housing treatment) were transported directly to the abattoir (Hormel Foods, Austin, Minnesota) on the same day. This ensured that pigs used for collection of meat quality data were subjected to similar conditions prior to slaughter (i.e. transport, rest and lairage time). Focal pigs were not mixed with other pigs prior to slaughter. Carcass ph, purge loss, glucose in purge, meat colour, firmness, marbling, drip loss, cooking loss, and Warner Bratzler shear force were conducted on a pork sample from each focal pig according to the standard procedures described by Leheska et al. (2002) and a taste panel was conducted for meat quality. For the taste panel, the chops were cooked to 71 8C using a Farberware grill. The chops were then cut up into equal sized pieces and served to eight panelists under red incandescent light. The pieces were evaluated by each panelist for tenderness, juiciness, flavor, and overall like using an eight-point scale Statistical analysis The data for behavioural observations, growth performance, carcass quality and meat quality were analyzed by least squares analysis of variance using the general linear model procedure multivariate analysis of SPSS statistical software (SPSS version 13, 2005). Each pen of pigs was the experimental unit for behaviour, growth performance and carcass quality, and each pig was used as the experimental unit for meat quality measurements. 3. Results Pigs housed in deep-litter, large group systems were more active (spent significantly more time standing and performing locomotory behaviours) and performed more exploratory behaviours (physical pen interactions) than pigs in conventional housing systems at 9, 17 and 22 weeks of age (P < 0.05; Table 1). There were more social tactile (pig) interactions at 17 weeks of age in the conventional compared to the deep-litter housing; however, no difference at 9 and 22

6 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) Table 1 Posture and behaviour of pigs housed in deep-litter, large group or a conventional housing system at 9, 17 and 22 weeks of age Deep-litter, large group Conventional S.E.M. Postures (% of observation time) Standing 9 weeks 50.8c 27.1d weeks 52.0a 37.3b weeks 41.9a 27.5b 3.86 Sitting 9 weeks weeks weeks Lying 9 weeks 42.6c 69.0d weeks weeks 50.1a 65.5b 3.92 Behaviours (frequency of occurrence-times/5 min/pig) Idle 9 weeks 42.3c 70.9d weeks 33.4a 50.5b weeks 38.4c 67.0d 6.21 Locomotory 9 weeks 10.2c 2.3d weeks 9.4a 4.3b weeks 7.9c 2.3d 1.14 Physical pen interactions 9 weeks 40.4c 22.7d weeks 51.7c 32.5d weeks 44.4c 20.5d 5.03 Social tactile interactions 9 weeks weeks 7.9a 13.3b weeks Aggressive behaviour 9 weeks weeks weeks Within rows, means with different letters (a, b), (c, d) and (e, f) are significantly different at P < 0.05, 0.01 and 0.001, respectively. weeks of age. There was no significant difference (P > 0.05) in aggressive among pigs in the two housing systems at 9, 17 and 22 weeks of age. The salivary cortisol concentrations were significantly higher (P < 0.05) in the deep-litter, large group-housed pigs at 9 weeks of age compared to conventionally housed pigs (Table 2). There were no significant differences in salivary cortisol concentrations between housing treatment at 17 and 22 weeks of age. Pigs in the deep-litter system consumed significantly more feed (P < 0.01) and as a result had a poorer (P < 0.01) feed to gain (Table 3) compared to pigs in the conventional housing system.

7 18 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) Table 2 Average salivary cortisol concentrations (ng/ml) of pigs at 9, 17 and 22 weeks of age in a deep-litter, large group or conventional housing system Age of pig (weeks) Deep-litter, large group Conventional S.E.M 9 5.7a 2.3b Within rows, means with different letters (a, b) are significantly different at P < Table 3 Average growth performance and carcass characteristics of pigs housed in a deep-litter, large group or conventional housing system Trait Deep-litter, large group Conventional S.E.M Initial weight (kg) Final weight (kg) Daily feed intake (kg/head) 2.9c 2.6d 0.03 Daily gain (g) Feed:gain 3.2c 3.0d 0.04 Carcass weight (kg) Dressing (%) Backfat depth (mm) Within rows, means with different letters (c, d) are significantly different at P < There were no significant differences in death loss or number of medically treated pigs between housing treatments. Pigs in the deep-litter, large group housing treatment showed significantly more exploratory behaviour (P < 0.05), had a shorter time to get to the novel object area (P < 0.05) (Area A) and had a shorter amount of time until they first interacted with the novel object. Pigs housed in the deep-litter, large group system also had more (P < 0.05) interactions with the novel object (Table 4). Pigs in the deep-litter, large group treatment had lower (P < 0.01) loin ph, more (P < 0.05) purge loss, more glucose in purge (P < 0.05) and were lighter in subjective colour (P < 0.05) than loins from conventionally housed pigs. There were no significant differences (P > 0.05) observed in the objective colour measurements of L *, a * and b *. Trained sensory panelists could not detect any differences in quality of pork from either of the housing treatments. There were no Table 4 Fear test observations of pigs housed in deep-litter, large group and conventional housing system Deep-litter, large group Conventional S.E.M No. of squares entered pre-test No. of squares entered during novel test 42.3a 28.4b 3.30 Time taken to get to novel object (Area A) (s) 42.6a 106.8b Total time in Area A (s) Time to first interaction with novel object (s) 49.6a 123.0b Total number of interactions with novel object 3.1a 1.7b 0.32 Within rows, means with different letters (a, b) are significantly different at P < Pigs that did not enter Area A (thus did not interact with the novel object) were given a maximum value of 180 s for the time taken to get to Area A.

8 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) Table 5 Meat quality of loins harvested from pigs raised in deep-litter, large group or a conventional housing system Deep-litter, large group Conventional S.E.M Loin ph 5.61c 5.71d 0.03 L * a * b * Purge loss (%) 1.51a 1.02b Glucose in purge (mg/dl) a 79.77b 5.00 Colour a 2.16a 2.63b 0.14 Marbling (%) Cooking loss (%) Av. Shear force (kg) Tenderness b Juiciness b Flavor intensity b Overall desirability b Within rows, means with different letters (a, b) and (c, d) are significantly different at P < 0.05 and 0.01, respectively. L * = lightness (L * value of 100 = pure white); a * = redness; b * = yellowness. a Colour score; 1.0 = pale pinkish gray to white, 2.0 = grayish pink, 3.0 = reddish pink, 4.0 = dark reddish pink, 5.0 = purplish red, and 6.0 = dark purplish red. b 1 = Extremely tough, dry, bland or undesirable; 8 = Extremely tender, juicy, intense, or desirable. significant differences (P > 0.05) in tenderness, juiciness, pork flavor, or overall desirability of pork produced from the two housing treatments (Table 5). Taste panelists also could not detect any presence of off-flavors such as metallic, sour, bitter, rancid, livery, peanutty, burnt, stale, or bloody in pork from either housing system. 4. Discussion The scientific literature is deficient in information on the behaviour, welfare, growth performance and meat quality of pigs housed in deep-litter, large group housing systems (i.e. continuous exposure to deep-litter bedding, groups of 80 or more pigs in a naturally ventilated system) compared to conventional housing systems. Our results demonstrate that pigs housed in deep-litter, large group systems are more active and perform more exploratory behaviours (physical pen interactions) than pigs in conventional housing systems at 9, 17 and 22 weeks of age. These results confer with similar work conducted by Morrison et al. (2003a) and Guy et al. (2002). One may conclude that this increase in activity within the deep-litter system was due to the extreme fluctuations in ambient temperature experienced by the pigs, however, these results confer with Morrison et al. (2003a) who investigated the behaviour of pigs in deep-litter grouphoused systems housed under more temperate environmental conditions, where pigs did not experience extreme temperature fluctuations. Furthermore, Honeyman et al. (2001) have shown that bedding in deep-litter systems can generate temperatures above 40 8C at cm depths and above 30 8C over approximately half of the bedded area. During cold months, the effective temperature experienced by hoop pigs is moderated by the pigs burrowing in the bedding and from heat generated by the bedding pack. There were more social tactile (pig) interactions at 17 weeks of age in the conventional compared to the deep-litter housing; however, no difference at 9 and 22 weeks of age. There was no significant difference (P > 0.05) in aggressive among pigs in the two housing systems at 9, 17

9 20 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) and 22 weeks of age. Morrison et al. (2003a) reported more aggressive and sexual behaviour in deep-litter, large group-housed pigs. However, in those studies, entire males were used as well as the fact that pigs in the deep-litter, large group treatment had 0.6 m 2 less pen space compared to this experiment. These two factors could significantly change the behaviour of the pigs. Entire males will naturally show more aggressive and sexual behaviour compared to gilts and castrated males, especially as they near sexual maturity (Cronin et al., 2003). The provision of more pen space in the current experiment may provide the opportunity for pigs to escape aggressive encounters. Morrison et al. (2003a) also showed that pigs in deep-litter, large group systems interact with their pen more, which concurs with the results of the present experiment. This experiment provided further information on the welfare of pigs in deep-litter, large group housing compared to conventional systems. The salivary cortisol concentrations were higher in the deep-litter, large group-housed pigs at 9 weeks of age compared to conventionally housed pigs (Table 2). There were no significant differences in salivary cortisol concentrations between housing treatment at 17 and 22 weeks of age. These data indicate that the transition from the conventional nursery accommodation (close to the 9 week sampling period) may have been more stressful for the deep-litter, large group-housed pigs (i.e. moving to a colder environment, increased group size, fighting, re-establishing new social groups in large deep-litter pens, increased activity, change in feeder type, etc.), whereas the pigs moved into the conventional grower may have had a less stressful transition (i.e. going into similar group sizes, warm environment, familiar conventional surroundings in terms of feeder type, pen space, etc.). However, since there were no differences in salivary cortisol between housing treatments at 17 and 22 weeks, there is an indication that the pigs in the deep-litter, large group system became accustomed to their surroundings over time. Deep-litter, large group housing also provides more opportunity for locomotion and environmental stimulation compared to conventional systems. Regardless of the housing system used to house pigs, the capacity and willingness of stockpeople to manage livestock and identify sick and injured pigs will ultimately influence the welfare of the animals. Extensive research has shown that the behaviour of the stockpeople, especially behaviours that evoke a fear response in pigs, influence the welfare and growth performance of pigs (Hemsworth et al., 1989, 1986). Furthermore, the technical skills and knowledge, job satisfaction, job motivation and commitment of the stockperson will also influence the success of group housing systems for pigs (see Hemsworth and Coleman, 1998). From a facility design and management perspective, conventional housing systems provide the unique opportunity to individually medicate and treat a pig as required. Deep-litter, large group housing systems should incorporate a separate pen or method of restraining individual pigs for short periods of time for medical intervention. These facility design and management factors will ensure that welfare is not compromised in either housing system. This experiment provided further information on the growth performance of castrated males in deep-litter, large group housing systems. Pigs in the deep-litter system consumed significantly more feed (P < 0.01) and as a result had a poorer (P < 0.01) feed to gain (Table 3) compared to pigs in the conventional housing system, which is consistent with findings in other experiments (Honeyman et al., 1999; Johnston and Morrison, 2004). Growth rate of pigs was not influenced by housing treatment. There was no significant difference in backfat due to housing treatment, however, this was expected since pigs were marketed at a specific weight, which may have equalized any differences in backfat between housing treatments. Other experiments have shown that pigs raised in deep-litter, large group systems are fatter and consume more feed than their traditionally housed counterparts (Honeyman et al., 1999; Gentry et al., 2002; Honeyman and Harmon, 2003; Johnston and Morrison, 2004). The increase in feed intake in the deep-litter housed pigs may have been partly

10 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) attributed to the cooler ambient temperatures experienced. Honeyman and Harmon (2003) have shown an eight percent increase in feed intake during winter to compensate for additional energy requirements for thermoregulation. There were no significant differences in death loss or number of medically treated pigs between housing treatments. Research on the effects of deep-litter, large group housing system on the behaviour of pigs when they are exposed to new and novel environments and the ultimate effect on pork quality is limited. Our results demonstrate that when exposed to a standard fear test, pigs in deep-litter, large group housing systems are more likely (P < 0.05) to explore the novel arena and the object (showed more exploratory behaviour), have a shorter time to get to the novel object area (P < 0.05) (Area A) and have a shorter amount of time until they first interact with the novel object. Pigs housed in the deep-litter, large group system also had more (P < 0.05) interactions with the novel object (Table 4). These data may indicate that pigs raised in deep-litter, large group systems may be easier to handle and move, adapt better to new and novel environments, and show more exploratory behaviour in a novel environment compared to conventionally housed pigs. Unfortunately, in the current experiment it was not possible to observe the pigs through lairage and at the time of slaughter, or obtain stress physiology measures at that time. Therefore, we assumed that the behaviour of the pigs in the standard novel test is representative of a novel environment that pigs may be exposed to at the time of slaughter. Obviously there are other factors such as time in transport, noise, scent of blood, etc. that were present at slaughter, which were not present in the standard fear test. Even though differences were observed in the behaviour of pigs housed in a deep-litter, large group housing system when exposed to a novel environment, these differences did not translate into improved pork quality. Pigs in the deep-litter, large group treatment had lower (P < 0.01) loin ph, more (P < 0.05) purge loss, more glucose in purge (P < 0.05) and were lighter in subjective colour (P < 0.05) than loins from conventionally housed pigs (Table 5). There were no significant differences observed in the objective colour measurements of L *, a * and b *. These pork quality results are within reasonable limits and do not indicate that the pigs in either housing treatment were stressed prior to slaughter. Stress prior to slaughter usually results in ph values in the range of , therefore, it is concluded that the ph, drip loss and colour results obtained in the current experiment would not lead to problems with PSE (pale soft exudative) or unfavourable pork from pigs from either housing system (see review by Terlouw, 2005; National Pork Board, 2005). Furthermore, despite significant differences in the objective measures of pork quality, trained sensory panelists could not detect any differences in quality of pork from either of the housing treatments. There were no significant differences in tenderness, juiciness, pork flavor, or overall desirability of pork produced from the two housing treatments. Taste panelists also could not detect any presence of off-flavors such as metallic, sour, bitter, rancid, livery, peanutty, burnt, stale, or bloody (data not shown) in pork from either housing system. From these data, it appears that deep-litter, large group housing systems or conventional systems as managed in this experiment, have no differential effect on eating quality of pork. These results are similar to those observed by Johnston and Morrison (2004) and Gentry et al. (2002) where there were no differences in pork quality between pigs housed in deep-litter, large group housing compared to conventional systems. It is difficult to compare deep-litter, large group housing systems to conventional systems, as experiments are often confounded by factors such as enrichment and pen space allowance. Regardless, it is necessary to compare systems as a whole, as have been conducted by Morrison et al. (2003a), Johnston and Morrison (2004) and Gentry et al. (2002). There have been limited studies conducted on the effect of environmental enrichment (i.e. straw, extra pen space) on pork

11 22 R.S. Morrison et al. / Applied Animal Behaviour Science 103 (2007) quality; however, these studies were conducted in conventional environments (i.e. slatted floors, small group sizes) with the addition of enrichment to the conventional environment (de Jong et al., 2000; Beattie et al., 2000; Klont et al., 2001). One must be careful not to extrapolate too much information from these experiments to the housing system used in this experiment as they are remarkably different in terms of the environment (i.e. smaller group sizes, slatted floors, reduced pen space, etc.). The research that has been conducted assessing pork quality from pigs housed in conventional systems with enrichment has shown conflicting results. Beattie et al. (2000) showed that pigs from enriched environments (addition of straw and extra pen space) produced pork which was more tender and with less cooking loss compared to pigs raised in a barren environment. On the other hand, Beattie et al. (1993) showed that pork was less tender from pigs raised in enriched environments. Edwards (2005) concluded that these pork quality differences observed by Beattie et al. (1993, 2000) may have been due to differences in growth rate and fatness of the carcasses. Klont et al. (2001) did not observe any differences in pork characteristics from pigs raised in enriched environments. These authors did observe that the pigs from the enrichment housing treatment had a higher water holding capacity and explained that these data may indicate differences in glycolytic potential at slaughter between the two housing treatments. Stress prior to slaughter can increase the glycolytic potential and cause postmortem breakdown of glycogen to lactate which will reduce the water holding capacity of the meat (Moss, 1984; Hambrecht et al., 2005). Klont et al. (2001) suggested that perhaps the pigs from the enriched housing system were better able to cope with the new situation of preslaughter stress, since cortisol concentrations were lower in pigs from the enrichment housing treatment at the time of slaughter. Nevertheless, regardless of the housing system in which a pig is raised, in the current experiment, enrichment within the pig s environment (i.e. extra pen space and continuous exposure to deep-bedding in deep-litter, large group housing systems) may have influenced the pig s behavioural response when exposed to a new environment such as transport and lairage; however, in the current experiment these behavioural differences did not improve pork quality, and pork quality measurements of ph, purge loss and colour showed that there was no indication of stress prior to slaughter. 5. Conclusion Pigs in deep-litter, large group systems were more active, performed more exploratory behaviours in their day to day environment and conducted more exploratory behaviours when exposed to a novel situation compared to pigs housed in conventional systems. These data suggest that pigs raised in a deep-litter, large group housing system may be easier to handle and may adapt better to new and novel environments. However, this change in behaviour did not improve pork quality. Measures of stress physiology and aggressive behaviour showed that over time there were no differences in the welfare of pigs between the two housing systems, however, pigs moved from conventional nursery accommodation into deep-litter, large group housing may take some time to adjust to their new environment. Acknowledgements We wish to acknowledge the financial support from the Minnesota Pork Producers Association, North Mankato, MN and Hormel Foods, Austin, MN, USA. Furthermore, the technical support of the staff at the University of Minnesota s, West Central Research and Outreach Center is greatly appreciated.

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