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The effect of space allowance on performance, aggression and
immune competence of growing pigs housed on straw
deep-litter at different group sizes
a,b ,
*
a a cS.P. Turner
, M. Ewen , J.A. Rooke , S.A. Edwards
a
Scottish Agricultural College, Ferguson Building, Craibstone Estate, Bucksburn, Aberdeen, AB21 9YA, UK
b
Scottish Agricultural College, Sir Stephen Watson Building, Bush Estate, Penicuik, Midlothian, EH26 0PH, UK
c
Department of Agriculture, University of Aberdeen, King Street, Aberdeen, AB24 5UA, UK
Received 29 June 1999; received in revised form 29 November 1999; accepted 17 December 1999
Abstract
Legislation controlling minimum floor space allowances for pigs rarely allows flexibility for variations in the physical and social environment. The space requirement of pigs housed in large groups and on deep-straw bedding has not been
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adequately addressed. Pigs, housed on deep-straw for 6 weeks in groups of 20 or 80, were provided with a low (50 kg / m )
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or high (32 kg / m ) space allowance in an experiment of 232 factorial design replicated four times. Low space allowance, irrespective of group size, did not influence average daily gain (ADG), but tended to improve efficiency of growth (P,0.1). Groups of 80 pigs had a lower ADG than groups of 20 (0.684 vs. 0.732 S.E.D. 0.0142 kg / day, P,0.01). Within pen variation in ADG was similar for each treatment. Number of skin lesions were elevated by low space allowance (10.1 vs. 8.5 s.e.d. 0.68 lesions per pig for low and high space allowance respectively, P,0.05). The humoral response to an antigen challenge (Newcastle disease virus) was lower when provided with small space allowance (P,0.01). Since the main effects did not interact, the poorer ADG of large groups, and the higher lesion score and suppressed immune response of pigs provided with lower space allowance, suggest that these conditions may independently compromise productivity and welfare. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Pig; Space allowance; Group size; Deep-litter, Performance; Immune response
1. Introduction the severity of this limitation often fail to consider aspects of the housing conditions such as the ambient In commercial housing systems, space is a re- temperature and floor type (Edwards et al., 1988). source which is limited in the interests of efficiency The majority of experiments to date have been of building utilisation. Recommendations governing carried out in housing with fully slatted floors or minimal bedding. In deep-litter systems, it might be predicted that a greater space allowance will be
*Corresponding author. Tel.: 144-131-535-3200; fax: 1
44-required for the maintenance of satisfactory pen
131-535-3121.
E-mail address: s.turner@ed.sac.ac.uk (S.P. Turner). conditions due to the increased level of activity
(Lyons et al., 1995), lack of a clearly differentiated was carried out to measure the performance, aggres-lying and excretory area and infrequent removal of sion and immune competence of pigs housed on excreta from within the pen. deep-straw bedding in either a conventionally sized No differential legislation or national codes exist group (20 pigs / pen) or a large group (80 pigs / pen) regarding the space requirements of pigs housed in when provided with a space allowance representative deep-straw bedded systems and values recommended of the upper or lower quartile of the range of space by different UK Quality Assurance schemes vary. allowances used in commercial practice for deep-However, a value of 15 square feet per growing or litter housing.
finishing pig housed on deep-straw has been rec-ommended widely in the UK based on commercial
experience (A.T. Smith, Agricultural Development 2. Materials and Methods and Advisory Service, personal communication; S.A.
Edwards, Scottish Agricultural College, personal 2.1. Experimental design and treatments communication). Expressed in terms of liveweight
per square metre of floor space, this equates to a A total of 800 Large White X Landrace growing
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mean stocking rate of 43 kg / m , allowing 22 kg / m pigs (start weight: 29.7 S.E. 0.16 kg) were housed on
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at the beginning of the growing phase and 64 kg / m deep-straw, and assigned, for 6 weeks, to one of four at the end of the finishing phase. For weaner pigs, a treatments. A 232 factorial arrangement, replicated value of eight square feet has also been suggested four times, of two group sizes and two space (P.I.C., 1994), which translates to a stocking rate at allowances, was used. The group sizes were 20 and
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the end of the weaner phase of 40 kg / m . However, 80 pigs, and the space allowances were 50 kg / m
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no critical experiments have been carried out on (low) and 32 kg / m (high). The groups of 20 were which to base such recommendations, and they are formed by mixing pigs from three smaller pens, and greatly in excess of current legislative requirements the groups of 80 from 12 pens, such that the mean (EC Council Directive 91 / 630). number of pigs taken from each original pen was To the list of factors which might influence space consistent. All animals experienced the same man-requirement may also be added the effect of varia- agement procedures and similar social and physical tions in the social environment. Although the in- environments before introduction to the experiment. fluence of variables such as group size have been The space allowance was maintained by a weekly studied in association with space allowance for many assessment of mean liveweight and the movement of years, the two factors have rarely been considered a partition to extend the pen length accordingly. The independently of each other (Krider et al., 1975; ratio of pigs to drinkers (10 pigs per bite drinker) and Mitchell et al., 1983; Kornegay and Notter, 1984). feeder space (61 mm trough length per pig) was Where these factors have been differentiated, the maintained constant. The percentage of males to group sizes adopted have consistently been small females was similar in each pen (54.2 S.E. 0.02% (Bryant and Ewbank, 1974; Brumm, 1996). The males) and did not significantly vary across treat-social environment in large groups of pigs has not ments. Dry pelleted feed was offered ad libitum been sufficiently described (Edwards and Turner, (19.5% crude protein, 5% crude fibre, 1.15% lysine, 2000), and the implications of this for space require- 13.3 MJDE / kg). The experiment was performed ments are unknown. The applicability of current between May and December and ambient tempera-legislation and recommendations regarding space ture was recorded daily for each treatment. Bedding allowance is therefore questionable under these was replaced at 4-week intervals and fresh straw was conditions. Since, for reasons of mechanisation of provided daily.
straw and manure handling, it is very common for
deep-litter systems to operate with large group sizes, 2.2. Performance it is necessary to evaluate whether this factor will
mean average daily feed intake (ADFI) and feed and the amount of rabbit anti-pig IgG bound to the conversion ratio (FCR) were calculated from records pig IgG coating each well was measured following of the weight of feed offered and that refused. the introduction of peroxidase-conjugated anti-rabbit IgG antiserum. The absorbence value was inversely 2.3. Activity related to the quantity of IgG present in the serum
sample.
Fifteen pigs, five each of heavy (34.9 kg S.E. Anti-Newcastle IgG in pig serum was measured 0.21), medium (29.6 kg S.E. 0.17) and light (24.5 kg using a modification of the FlockscreenE non-com-S.E. 0.18) start weight, were selected from each pen. petitive ELISA assay for chicken serum (Guildhay The activity, classified as active (running, walking, Ltd., Surrey, UK, kit number V120); alkaline phos-standing, sitting) or inactive (lying) was recorded for phatase-conjugated donkey anti-chicken IgG was each of these 15 pigs at weeks 0, 2, 4 and 6. Sixteen substituted with alkaline phosphatase-conjugated rab-recordings were made at 15-min intervals, with eight bit anti-pig IgG. Alkaline phosphatase activity was observations being performed on each of two con- measured at 550 nm using phenolphthalein mono-secutive days during these weeks. A single observer phosphate as substrate. Amounts of porcine anti-therefore made 64 recordings per animal. Newcastle IgG were expressed as arbitrary absorb-ence values. The ELISA assay utilised a highly 2.4. Aggression purified viral sub-unit antigen selected for its high specificity towards paramyxovirus serotype 1 organ-The skin lesion score of the sample pigs used for isms and which would not cross-react with organ-the assessment of activity was recorded at 4 days isms of paramyxovirus serotypes 2 and 3.
post-mixing, and at the end of the first and all
subsequent weeks. Fresh cuts, scratches and abra- 2.6. Statistical analysis sions were counted by a single observer throughout.
All parameters were assessed using pen means as 2.5. Immune competence the statistical unit by analysis of variance on the Minitab computer program (Minitab Inc., PA, USA), Six pigs per pen, two each of heavy, medium and incorporating as factors, replicate, space category light weight classes, were randomly selected from and group size and their interaction. The influence of the sample pigs used for the activity analysis. A treatment on immune competence was also analysed blood sample was taken via jugular venepuncture by a repeated measures analysis of variance using as after 2 weeks on trial and was immediately followed factors, replicate, space category, group size, week of by an intra-muscular injection of 2 ml inactivated sampling and the interactions. The effect of
treat-
Newcastle disease virus (Nobilis Newcavac, Inter- ment on different focal pig weight categories was vet UK Ltd., Cambridge, UK). After 4 weeks on examined using analysis of variance on each weight trial, a blood sample was taken and again followed category independently. The number of animals by a second injection of Newcastle disease virus. A removed from the experiment due to ill health was third blood sample was collected after 6 weeks on compared across treatments by a chi-squared test. trial. Following centrifugation, serum samples were
analysed for total IgG concentration and Newcastle
virus specific IgG. 3. Results Total IgG (mg / ml) was measured using a
com-petitive ELISA technique (Varley et al., 1985). To 3.1. Ambient temperature ELISA plates coated with a known amount of
pens housing groups of 80 pigs than groups of 20 weight was categorised into quartiles, and the ADG (14.2 vs. 13.4 S.E.D. 0.298C), but no difference was of pigs in the lower and upper quartiles examined apparent in the daily maximum temperature. individually. This indicated a suppression of growth for all pigs, regardless of initial weight, when in a 3.2. Performance large group, rather than a continuous divergence in
performance between light and heavy individuals. Neither the start weight or coefficient of variation
(C.V.) of start weight varied across treatments. Start
3.3. Health weight, assessed as a covariate, did not significantly
influence any of the performance parameters, and
Rectal prolapse (six cases) and hind-leg lameness was therefore excluded from the analysis. No
inter-due to a chronic Mycoplasmal infection (11 cases) actions between group size and space were recorded,
were the principal reasons for the removal of animals so main effects only are presented in Table 1. Space
from the experiment. The number of pigs removed allowance did not significantly influence the average
from the experiment due to ill health was not daily gain (ADG), but pigs in the smaller space
significantly influenced by treatment. allowance tended to consume less feed, and therefore
grow more efficiently (lower FCR) (P,0.1). The
ADG for the 6-week trial period was significantly 3.4. Activity depressed in groups of 80 compared to 20 pigs,
irrespective of space allowance (0.684 vs. 0.732 The percentage of the 64 recordings of activity S.E.D. 0.0142 kg / day, P,0.01). This effect was not where the focal animal was recorded as lying was significant during the first 2 weeks post-mixing, but, not significantly affected by treatment (mean all over this period, the C.V. of ADG tended (P,0.1) to treatments 34.7 S.E. 2.23% of observations the pig be higher in the larger groups. Within each pen, start activity was recorded as lying).
Table 1
Performance parameters for the two space allowances and group sizes
Treatment S.E. Significance
20 pigs 20 pigs 80 pigs 80 pigs Group Space
size
2 2 2 2
32 kg / m 50 kg / m 32 kg / m 50 kg / m
Start weight (kg) 28.9 29.9 29.1 29.6 0.05 NS NS
C.V. start weight (%) 13.3 11.9 13.4 14.0 0.85 NS NS
ADG(kg /pig per day):
Weeks 0–6 0.719 0.745 0.682 0.685 0.0142 ** NS
Weeks 0–2 0.591 0.537 0.545 0.504 0.0368 NS NS
C.V. ADG (%)
Weeks 0–6 14.6 13.4 15.4 14.3 1.21 NS NS
Weeks 0–2 20.0 21.5 27.5 29.6 3.20 P,0.1 NS
ADG weeks0 –6 : Lower quartile
Start weight 0.656 0.677 0.624 0.622 0.0152 * NS
Upper quartile
Start weight 0.805 0.809 0.744 0.743 0.0206 * NS
Table 2
Lesion score values for pooled sample pigs and for differentiated weight classes
Treatment S.E. Significance
20 pigs 20 pigs 80 pigs 80 pigs Group Space
size
Medium pigs 6.6 9.4 9.1 7.3 0.69 ** interaction
Light pigs 9.2 11.5 8.1 7.9 0.96 * NS
Day4 :
All pigs 17.3 15.7 17.4 13.0 3.19 NS NS
Heavy pigs 20.7 20.2 21.7 21.0 5.38 NS NS
Medium pigs 12.7 13.8 18.3 10.1 2.54 NS NS
Light pigs 18.6 13.3 12.4 7.8 3.84 NS NS
3.5. Aggression when in a small group and given the more generous space allowance (P,0.01), while light weight pigs When treatments were pooled, heavy pigs had had the lowest lesion score when in a group of 80 significantly more lesions than either medium or (8.0 vs. 10.4 S.E.D. 0.68 lesions / pig for group sizes light weight pigs on the 4th day post-mixing of 80 and 20 respectively, P,0.05).
(20.8611.29, 13.765.48 and 13.067.60 lesions per
pig respectively, P,0.05). Considering the mean 3.6. Immune competence lesion score for the total 6 week period, a trend was
still apparent (P,0.1). Overall, a larger space
Total IgG concentration did not change between allowance was associated with a lower lesion score
weeks 2, 4 and 6 and was unaffected by treatment. (8.4 vs. 9.8 S.E.D. 0.42 lesions per pig, P,0.05,
Anti-Newcastle virus IgG concentration increased Table 2). The lesion score of the heavy, medium and
significantly following each of the two challenges light weight pigs were also considered separately,
(0.2560.046, 0.7860.198 and 1.03960.215 absorb-during both the full 6-week period and after 4 days
ence at 550 nm in weeks 2, 4 and 6 respectively, on trial (Table 2). Heavy pigs displayed the fewest
P,0.001). The basal titre of serum anti-Newcastle lesions when given the more generous space
allow-IgG, before injection of the antigen, was significantly ance over the 6 weeks (8.6 vs. 11.2 S.E.D. 0.63
higher in the groups of 80 than 20 (Table 3). The
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lesions / pig for 32 and 50 kg / m , respectively).
week 2 value was therefore included as a covariate in Medium weight pigs displayed the fewest lesions
the assessment of the week 4 and 6 titres. Week 4
Table 3
Treatment effects on concentration of anti-Newcastle IgG (absorbence at 550 nm)
Week Treatment S.E. Significance
20 pigs 20 pigs 80 pigs 80 pigs Group Space
size
response to injection of Newcastle virus was sig- ing phase (80 kg), the current UK legislation stipu-nificantly poorer in pens with the lower space lates a minimum acceptable area which is over 2.5 allowance (P,0.01). Alternative analysis by re- times smaller than that recommended for the same peated measures analysis of variance also showed a animal on deep-litter. The extrapolation of space significant effect of space allowance (P,0.05). requirements calculated for pigs housed on slatted When treatments were pooled, there were no associa- flooring to those on deep-litter is inappropriate with tions between liveweight category and total IgG or current evidence.
anti-Newcastle IgG concentration during any sam- Spoolder et al. (1997) have examined the effects pling period. No clear interactions existed between of providing fully slatted, solid flooring without pig weight class and treatment for either total IgG or bedding, and straw bedded ‘Straw Flow’ flooring to anti-Newcastle IgG, suggesting that no environment finishing pigs maintained at the minimum space disproportionately compromised the immune system allowance accepted in the Welfare of Livestock of a given weight class of pig. Regulations (1994). No differences in performance, weight of adrenal glands or stomach or heart abnor-malities were apparent between treatments. Skin 4. Discussion damage was lower in animals housed on solid floors without straw bedding but this may have resulted In the present experiment, space allowance and from greater soiling in those pens. These findings group size did not interact, providing no evidence for would suggest that floor type had minimal effect on a need to specify different space requirements in the validity of extrapolating space allowance require-deep-litter systems for animals in large or small ments between flooring systems under the conditions groups. The two main factors will therefore be studied, but all systems had regular excreta removal discussed separately. from the surface of the excretory area of the pen, Current UK legislation describes the floor space rather than being deep-litter. In the current experi-requirements of pigs housed on partially or fully ment, performance was not depressed by the lower slatted floors (Welfare of Livestock Regulations, space allowance. Indeed, a space allowance of 50
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energy expended during, and consequent on, active ADG than those in groups of 20, irrespective of behaviours may have been greater in pens with a space allowance. This difference was not apparent large space allowance or of large dimensions. during the first 2 weeks post-mixing. The depression Despite the findings of Spoolder et al. (1997) and in ADG may have been a chronic response to the the similarity in performance between pigs offered dimensions of the pen requiring greater locomotory the low and high space allowance in the present activity to move between different pen areas and experiment, the greater skin lesion score and poorer thereby increasing the use of energy for exercise, or humoral immune response following the first in- the continued presence of a large number of other jection of the Newcastle disease antigen in the more animals rather than a manifestation of mixing per se. restricted space allowance would suggest that stress However, the elevated coefficient of variation in was experienced to a greater extent when the space ADG in the larger groups during only the first 2 allowance was low. An elevation in lesion score at weeks post-mixing, which was not found for the the lower space allowance may reflect a difficulty in mean of the 6 weeks would dispute this.
escaping from the immediate vicinity of an aggressor Previous experiments examining the effects of due to the close proximity of pen mates, or the large group size on performance have given incon-interference of a fight leading to an inconclusive clusive results (Edwards and Turner, 2000). Nielsen result and the need for future aggression (Bryant and (1992) reported a significant linear association be-Ewbank, 1972; Baxter, 1985). The fact that the tween a decreasing ADG with increasing group size lesion score value was not significantly different for when weaner pigs were housed in groups of 15, 30, animals in groups of 20 and 80 at the same space 60 or 120. Similarly, Pedersen (1990), described a allowance would suggest that the physical dimen- slight reduction in ADG of growers maintained in sions of the pen were of little importance in imped- groups of 48 compared to groups of 16. Nielsen ing escape. (1989) also found a depression in ADG of weaners The possible link between stress, such as that housed in pens with a mean of 88 animals per pen resulting from aggression, and a compromised im- compared to cages with nine animals, although it is mune response has been reviewed and advocated by difficult to quantify the contribution that differences von Borell (1994). The depressed immune response in the physical environment and management may in pigs housed at the low space allowance in the have made to this effect. Spoolder et al. (1999) present experiment may be a manifestation of the found a depression in ADG between 36 and 65 kg stress associated with prolonged aggression. This is liveweight with increasing group size of 20, 40 or 80 in agreement with the findings of Barnett et al. pigs housed on a part slatted floor. From 65 to 85 kg (1992). Reducing the space allowance for gilts from no difference was apparent, and Turner et al. (1999)
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1.97 to 0.98 m per pig was associated with a rise in reported no significant difference in ADG of growing total and free cortisol concentrations and a smaller pigs housed on slats in groups of 20 or 60.
change in skinfold thickness following injection with In the studies by Pedersen (1990), Nielsen (1992) a mitogen, indicative of a poorer cell-mediated and Spoolder et al. (1999) within pen variation in immune response. ADG was similar for each group size. The poorer It was suggested by Petherick (1983) that be- performance of pigs with both a lower or an upper havioural and performance indicators of stress at- interquartile start weight in the large groups in the tributable to a large group size would only become present experiment would also suggest that the large apparent when floor space allowance was restricted group size did not specifically penalize light weight below a threshold level. Evidence has been presented animals. This is further supported by the presence of which suggests that stress was associated with a the lowest lesion score values of the light weight
2
reduction in space allowance from 32 kg / m to 50 pigs in the groups of 80, especially immediately after
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Furthermore, the similarity in immune competence ventilation, health status and management standard between light and heavy pigs, mean lesion score and procedure from that in the present experiment value of all weight categories of pigs and ADFI, may may demand a reconsideration of this conclusion. suggest that the depression in ADG was in response
to the energy cost associated with the greater
locomotory activity required to access resources and Acknowledgements the scope for exploration offered in the larger pen.
The reason for the higher basal titre of anti- We thank the staff of Tillycorthie Farm for their Newcastle virus IgG, before vaccination, in pigs assistance and Intervet UK Ltd. for the provision of housed in groups of 80 is unknown. The housing vaccine. S.P. Turner is in receipt of a scholarship conditions and management experienced before in- from the Cruden Foundation. S.A. Edwards receives troduction to the experiment were the same for each financial support from SERAD.
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