Directory UMM :Data Elmu:jurnal:L:Livestock Production Science:Vol63.Issue2.Apr2000:
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Aggression among finishing pigs following mixing in kennelled
and unkennelled accommodation
a ,
*
b ,1 a ,2H.A.M. Spoolder
, S.A. Edwards
, S. Corning
a
ADAS Terrington, Terrington St. Clement, King’s Lynn PE34 4PW, UK b
SAC Aberdeen, The Ferguson Building, Craibstone, Bucksburn, Aberdeen AB1 9YA, UK Received 3 September 1998; received in revised form 10 March 1999; accepted 17 May 1999
Abstract
This study examines the interactive effects of mixing and the provision of kennels to finishing pigs on agonistic behaviour. Pigs were housed either in naturally ventilated kennelled accommodation, or in an unkennelled sloping floor accommodation with automatically controlled natural ventilation (ACNV). Under each of these two housing conditions, three groups of 10 pigs were subjected to one of the following four mixing / moving treatments: no mixing (control), mixing and moving at 55 kg only, mixing and moving at 75 kg only and mixing and moving on both occasions. Groups which were not mixed at 55 kg or at 75 kg were moved to a novel pen at the time that the others were mixed. Mixing and moving pigs resulted in higher levels of aggression and skin damage compared to moving only. Levels of skin lesions were lower when mixing at 55 kg compared to mixing at 75 kg. The duration and frequency of fights in the immediate post mixing period and skin damage measured on day 1 after mixing correlated well when mixing pigs at 75 kg, but not when mixing at 55 kg. This suggests that the hierarchy takes longer to be established in younger pigs than it does in older heavier pigs, or that skin damage inflicted by heavier pigs during fights is more severe. Previous mixing at 55 kg had minimal effects on mixing at 75 kg in terms of behaviour immediately post mixing and skin lesions in the following two days. The presence of a kennel appeared to have a positive effect on the average duration of fights, but the effect on the proportion of fights which involved location changes (lying to dunging area or vice versa) was not significant. Performance data suggested that food conversion ratios were poorer in the first two weeks after mixing in the kennelled building, but not in the sloping floor building. Increased social and thermal stress after mixing in the kennelled, naturally ventilated accommodation may have been the cause of this. Over the whole of the finishing period, daily live weight gains and food conversion ratios did not differ measurably between treatments. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Pig; Finishers; Housing system; Aggression; Mixing
*Corresponding author. Present address: Praktijkonderzoek Veehouderij, Runderweg 6, 8219 PK Lelystad, The Netherlands.
Tel.: 131-320-293-211; fax: 131-320-241-584. 1. Introduction
E-mail address: [email protected] (H.A.M.
Spool-der) European Union (EU) Council Directive 91 / 630 /
1
Present address: University of Aberdeen, Department of
Ag-EEC, which lays down minimum standards for the
riculture, 581 King Street, Aberdeen AB24 5UA, UK.
2 protection of pigs, states that ‘‘Pigs should be kept in
Present address: PIC, Fyfield Wick, Abingdon OX13 5NA,
UK. stable groups with as little mixing as possible’’. This
0301-6226 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. P I I : S 0 3 0 1 - 6 2 2 6 ( 9 9 ) 0 0 1 2 1 - 9
(2)
rule has been adopted as mixing pigs almost study, this principle was tested by addressing
loca-inevitably leads to aggression in order to re-establish tion changes during aggressive interactions following
the dominance hierarchy in the group. Potentially, mixing. Two housing systems were used. The first
the elevated levels of aggression in the group will system offered a ‘‘barrier’’ in the form of a kennel
result in increased risk of death or injury, an increase wall separating a scrape through dunging passage
in the number of skin lesions (with associated and a strawed kennel. The other consisted of a
implications for welfare and health) and a reduction rectangular pen with a strawed lying area and a
in growth. In practice, mixing of finishing pigs may scrape through dunging passage, and no physical
occur when a change of pen becomes necessary to barrier to separate the two. The study aimed to
increase space allowance as the animal grows, or investigate the effects these commercially used
sys-when heavier pen mates are being marketed and the tems have on aggression in groups of finishers
remaining pigs are put together in one pen. In both immediately after mixing.
cases mixing will allow the producer to make better use of his facilities. The latter situation occurs
primarily in the final weeks of the finishing period. 2. Materials and methods
In the present study, pigs were mixed either not at
all, at a weight when pen changes may become 2.1. Treatments
necessary (55 kg), just prior to slaughter (75 kg) or
on both occasions. This last treatment also allowed The experimental design was a 234 factorial.
the hypothesis to be tested that pigs learn social The two factors under investigation were housing
skills when mixed more than once (see: Van Putten system and frequency of mixing. System 1 was the
and Burl«, 1997; Dingemans et al., 1993). kennelled system (K). Each pen had a 3.132.6 m
Various methods, including mixing at different scrape through dunging area, and a 2.631.2 m straw
times of the day (Barnett et al., 1994; Barnett et al., bedded kennel. The building was naturally
venti-1996), the administration of tranquilising drugs (e.g., lated. Pens in system 2 had an insulated 1:16 sloping
Luescher et al., 1990; Tan and Shackleton, 1990) and floor (S) of 4.832.0 m, and a level 2.032.0 m
the dimming of light from 100 to 5 lx (Christison, scrape through dunging area. Straw was provided
1996) have been tested for their potential to reduce from a rack at the top of the slope. An automatically
aggression during mixing. In general, these methods controlled natural ventilation (ACNV) system was in
only showed a reduction in aggression in the initial operation, set to maintain room temperature at 178C.
stages, by delaying the settling of the social hierar- The mixing treatments consisted of mixing pigs at
chy; skin lesions between controls and treatments are either 55 or 75 kg live weight. All mixing treatments
often not different in the days following mixing. In were applied by moving half the animals in a group
sows, Edwards et al. (1993) used a central, sus- to one pen, and the other half to another. Animals
pended barrier in a mixing pen and found that this were selected at random. They were there joined by
reduced the frequency of fights. In weaners, Waran pigs from another group on the same mixing
treat-and Broom (1993) found a comparable effect of an ment, to make up original numbers. Groups which
opaque barrier: the frequency of aggressive interac- were not mixed were moved as a group to another
tions was reduced by 40% during the first week after pen. Mixing / moving at 55 kg will from here on be
weaning in pens with a barrier fitted. The authors of referred to as ‘‘Mix 1’’ whereas mixing and moving
both studies argue that the provision of a barrier at 75 kg will be referred to as ‘‘Mix 2’’. Table 1
allows the pig which is attacked to disappear out of explains the four resulting mixing treatments.
the view of the aggressor, thereby ‘‘solving’’ the
dispute effectively, with a minimum of interactions. 2.2. Animals and management
Other authors failed to confirm this hypothesis by
looking at aggression and skin lesions in pens with Animals were allocated to their treatments in
artificial partitioning (e.g., weaners: Olesen et al. groups of 14 at an approximate average live weight
(3)
Table 1 2.3. Observations The four mixing treatments applied in each of the two housing
systems
Data were collected on behaviour, skin lesions and
At 55 kg (Mix 1) At 75 kg (Mix 2) daily live weight gain of the animals in the post-Treatment C (control) Moving only Moving only mixing period.
Treatment A Mixing and moving Moving only
Treatment B Moving only Mixing and moving 2.3.1. Behaviour Treatment D Mixing and moving Mixing and moving
Behaviour observations were carried out on four focal pigs in each group of 10 (two male, two
the size of the group was reduced to 10 pigs (half female). These four pigs were selected on the basis
male, half female). The initially larger group size that their weight was as close as possible to the
was necessary to avoid potential thermal problems average of the group. Ad libitum sampling, a
tech-due to under stocking the building when pigs were nique which records all instances of a particular type
small, and to allow for any pigs dropping out prior to of behaviour and the circumstances related to it
the start of the treatments. Pigs were sold at an (Martin and Bateson, 1993) was used. In the present
approximate average live weight of 85 kg. Each of study, all aggressive interactions involving any of the
the eight treatments had three replicate pens, giving a four focal animals were recorded (see Table 2). In
total of 24 pens (240 animals). During the experi- addition, activity levels (active / inactive) and location
ment pigs were fed ad libitum from a single space (lying area / dunging area) of focal animals were
hopper. Water was provided ad libitum. Straw was recorded on a continual basis. The observation
available to animals on the S treatments from a straw periods started immediately after the moving and
hopper, which was topped up daily. Pigs on the K mixing treatment was applied, and lasted for 2 h.
treatment were given half a bale of straw per pen per Husky Hunter16 computers, mounted with the
be-day. One third of this straw was put into the kennel, haviour observation package Observer 2000 (Noldus,
and the rest was used to replace the scraped out Wageningen, The Netherlands) were used to collect
straw in the dunging passage. the data.
Table 2
Scoring system for aggressive interactions Behaviour Description
K Knock or threat
]]]]
The challenge consists of little more than thrust or a knock with closed mouth by the initiator, which the recipient either ignores, or responds to with a similar reaction
B Bite
]
The challenge is a bite and / or the recipient responds with a single bite after which the interaction is resolved O One-sided fight
]]]]
The challenge results in a series of bites from either the initiator or the recipient, showing a complete control of one animal over the situation
T Two-sided fight
]]]]
The challenge is not resolved immediately and a prolonged fight determines the eventual winner
I Inactive
]]
The animal is asleep or inactive
A Active
]]
(4)
2.3.2. Skin damage housing system. Tukey’s HSD was used for
pair-Skin damage was assessed on focal animals on the wise comparison of the means of the treatments
day before each of the two mixing / moving treat- (Minitab, 1993). Strong tendencies (0.05,P,
ments were applied, on the day after mixing, at day 7 0.10) have also been indicated in the tables.
after Mix 1 and on day 5 after Mix 2. The assess-ment consisted of a count of the number of skin
lesions (bruises, scratches and wounds) per area: 3. Results
front (from snout to middle of back), rear (from
middle of back to tail) and tail. Skin damage was 3.1. Behaviour
recorded using the Husky Hunter16 portable
com-puter. The frequency and average duration of a number
of behavioural parameters were higher in groups
2.3.3. Performance which were mixed and moved, compared to groups
All pigs on the experiment were weighed on entry which were only moved (Table 3). However, during
to the treatments, at Mix 1, two weeks after Mix 1, at Mix 1 the incidence of minor aggressive interactions
Mix 2 (approximately one week before slaughter) such as knocks and threats were higher in the groups
and at slaughter. A record was kept of all food added which were moved only, compared to groups which
to the single space hoppers in both buildings to give were mixed as well as moved.
total food consumption of the group. From these data There was some indication that the intensity of the
the food conversion ratio (FCR), the voluntary food aggressive interactions was greater during Mix 1
intake (VFI), as well as average daily live weight compared with Mix 2. During Mix 1 there was a
gain (DLWG) could be calculated. higher frequency of one-sided fights across all four
treatments (Mix 1 vs. Mix 2: 0.600 vs. 0.198;
2.4. Statistical analyses F1,18256.81; P50.010), and a higher frequency of
knocks / threats (Mix 1 vs. Mix 2: 12.53 vs. 8.41;
For the analysis of the behavioural data, the four F1,18257.72; P50.006) compared to Mix 2.
randomly chosen focal pigs were the experimental Prior mixing experience did not appear to affect
units, with a correction for group effects in the the aggressive behaviour of pigs during the 2 h
analyses of variance through blocking (Genstat 5 following a subsequent mix. The only indication that
Committee, 1987). The performance data were ana- mixing at 55 kg may have had an effect on behaviour
lysed for each separate time period in between during mixing at 75 kg was found in the frequency
weighings, and across the whole of the finishing of biting: move (at Mix 1) vs. moving1mixing (at
period. As experimental unit the pen was used (when Mix 1): 3.2 vs. 4.8 bites at Mix 2, respectively;
comparing within time periods) or the individual F1,8853.3; P50.073.
(when comparing across the whole finishing period, The behaviour of the pigs was affected by the
as pen composition changed as a consequence of layout of the pen (Table 4). However, the effects of
most treatments). Transformations were used where housing system on aggression immediately
post-mix-data did not meet the requirements of the analysis of ing was not the same during Mix 1 and Mix 2.
variance in the following order: angular, square root During Mix 1, the incidence of aggressive
interac-and logarithmic transformation. Data which could tions and the duration of fights appeared to be lower
not be normalised, were analysed using non-paramet- in the K compared with the S treatment.
Further-ric techniques. The two treatment factors were more, the average duration of one-sided fights was
mixing treatment and housing system. There were no longer in K pens. The frequency of aggression after
blocking factors. Interactive effects of mixing treat- the second Mix was greater in the K pens, although
ment at 55 kg and mixing just before slaughter were the average duration of two-sided fights was still
tested for by using Mix 1 (at 55 kg) and Mix 2 (at longer in the S pens (Table 4).
one week before slaughter) as treatment factors. The percentage of aggressive interactions which
(5)
Table 3
Levels of aggression (per focal pig, per 2-h observation period) and general activity in groups of finishers which were mixed and moved, compared to pigs which were only moved
Behaviour Treatment
Move Mix1move P-value
a a
Mean 95% C.I. Mean 95% C.I.
Mix1
Knock / threat (freq.) 17.1 12.3–22.7 8.7 6.7–10.9 ,0.001
Biting (freq.) 4.2 2.7–6.1 5.8 4.6–7.1 NS
One-sided fights (freq.) 1.5 0.8–2.5 3.2 1.8–5.1 0.030
Two-sided fights (freq.) 2.5 1.5–3.8 2.7 1.4–4.5 NS
b
One-sided fights (av. duration) 16.3 10.9–22.8 14.4 10.0–19.6 NS
b
Two-sided fights (av. duration) 20.0 7.3–54.9 27.6 19.8–38.4 0.094
b
Inactivity (duration) 2887.0 2437–3337 3646.0 3268–4023 0.007
c
Mix2
Knock / threat (freq.) 9.3 7.2–11.6 7.5 5.2–10.2 NS
Biting (freq.) 2.0 1.3–2.9 6.5 4.8–8.4 ,0.001
One-sided fights (freq.) 0.1 0.09–0.14 0.6 0.4–0.9 ,0.001
Two-sided fights (freq.) 0.1 0.08–0.14 3.7 2.6–5.3 ,0.001
b
One-sided fights (av. duration) 14.8 7.6–24.4 14.1 10.4–18.4 NS
b
Two-sided fights (av. duration) 18.0 12.7–25.6 27.1 19.1–38.4 0.060
b
Inactivity (duration) 3343.0 2882–3803 3374.0 2975–3772 NS
a
As most variables had to be transformed prior to analysis, standard errors could not be calculated. The back transformed 95% confidence interval is therefore presented here.
b
All durations are in seconds. c
Please note that at Mix 2 half the groups which were ‘‘mixed and moved’’, had only been ‘‘moved’’ at Mix 1 (i.e., treatment B groups). Conversely, half the groups which were ‘‘moved’’ at Mix 2 had been ‘‘mixed and moved’’ at Mix 1 (treatment A groups).
the kennel into the dunging area or vice versa) was kg appeared to have less skin damage immediately
higher immediately after pigs had been mixed and after mixing at 75 kg (day 1 after Mix 2: 15.2 vs.
moved compared with pigs which had only been 22.9 lesions per pig for mixing1moving at Mix 1
moved (e.g., one-sided fights: 10.0 vs. 32.5% for vs. moving only at Mix 1; F1,9059.99; P50.004).
moved vs. mixed1moved respectively; F1,36513.9; This effect had disappeared five days after the
P,0.001; Table 5). Differences in this parameter second mix. The effects of treatments on changes in
between the two housing systems were not signifi- skin lesion scores are presented in Table 6.
cant (e.g., one-sided fights: 26.3 vs. 16.2% for K vs. The increase in skin lesions differed between the
S, respectively; F1,3652.83; P50.101). two housing systems. After Mix 1, K pigs had a
higher increase in skin lesions between day 21 and
3.2. Skin damage day 7 than S pigs. After Mix 2 this was reversed,
with S pigs showing a greater increase in lesions
There was a significant effect of the mixing between days 21 and 1, as well as between days
treatment at Mix 1 on the level of skin lesions after 21 and 5 (Table 7).
Mix 1 (e.g., day 1 after Mix 1: 20.3 vs. 12.7 lesions Aggressive behaviour during the first 2 h after Mix
per pig for mixing1moving vs. moving only; 1 was not related to the increase in skin lesions
F1,92511.13; P50.001). Similarly, mixing and measured on day 1 after Mix 1, nor was it associated
moving (as opposed to moving only) at Mix 2 with changes measured at day 7. Following Mix 2
resulted in a higher number of skin lesions after Mix there was a high degree of correlation between the
2. A significant effect of Mix 1 was found on skin increases in skin damage from day 21 to day 1 and
(6)
Table 4
Effects of housing system on duration (in seconds) and frequency of aggressive behaviours per focal pig during the first 2 h after mixing
Behaviour Building
Kennelled Sloping floor P-value
a a
Mean 95% C.I. Mean 95% C.I.
Mix1
Knock / threat (freq.) 10.6 8.3–13.2 15.9 10.9–21.8 0.059
Biting (freq.) 5.9 4.4–7.4 7.0 5.1–8.9 NS
One-sided fights (freq.) 2.2 1.3–3.4 2.3 1.3–3.6 NS
Two-sided fights (freq.) 1.4 0.8–2.2 4.5 2.9–6.4 ,0.001
b
One-sided fights (av. duration) 12.0 7.9–16.9 19.5 11.8–29.2 0.003
b
Two-sided fights (av. duration) 3.0 1.1–8.5 3.3 1.4–7.6 NS
b
Inactivity (duration) 3154.0 2766–3541 3402.0 2901–3902 NS
Mix2
Knock / threat (freq.) 12.3 9.3–15.8 5.3 4.2–6.5 ,0.001
Biting (freq.) 3.9 2.8–5.2 4.0 2.6–5.8 NS
One-sided fights (freq.) 0.3 0.1–0.7 0.1 0.0–0.2 0.092
Two-sided fights (freq.) 1.1 0.5–2.3 0.4 0.2–1.0 0.053
b
One-sided fights (av. duration) 15.6 10.7–21.5 12.9 8.5–18.2 NS
b
Two-sided fights (av. duration) 16.6 11.8–23.5 36.5 26.2–50.8 ,0.001 b
Inactivity (duration) 3400.0 2986–3813 3273.0 2819–3726 NS
a
As most variables had to be transformed prior to analysis, standard errors could not be calculated. The back transformed 95% confidence interval is therefore presented here.
b
All durations are in seconds. Table 5
Percentage of interactions which resulted in a change of location (lying area vs. dunging area) for one or both of the animals involved Behaviour Building
Kennelled Sloping floor P-value
Moved Mixed Moved Mixed S.E.D. Housing Mixed Interact.
a
Knock / threat 0.16 0.41 0.15 0.20 – NS NS NS
a
Biting 0.09 0.45 0.03 0.79 – NS 0.009 NS
One-sided fights 17.0 35.7 3.0 29.3 8.6 NS ,0.001 NS
Two-sided fights 13.4 32.0 11.1 42.1 5.5 NS ,0.001 NS
a e
An log transformation had to be used prior to data analysis. Means are back transformed values. S.E.D.s could not be calculated.
during the first 2 h after mixing and moving (e.g., ing. In the kennelled building, both after Mix 1 and
correlation between total duration of two-sided fights after Mix 2, DLWG was lower in the groups which
and skin lesion score: r50.620; n596; P,0.001). were mixed compared to the groups which had only
No such relationship was found between skin lesions been moved. No such effect was found in the sloping
at day 1 and other behavioural variables such as floor building (see Table 8). In both buildings
biting and knocks or threats. however, food intakes did not differ in the periods
immediately following mixing (e.g., food intake in
3.3. Performance kennelled building during two weeks following Mix
1: 2.42 vs. 2.46 kg per day, for mixing1moving vs.
Treatment effects on daily live weight gain ap- moving only; F1,850.28; NS). As a result food
peared to differ between the two housing systems, conversion ratios were poorer under the mixing1
(7)
Table 6 a
Increase in levels of skin damage recorded between days 21 and 1, and days21 and 7 or 5 (all relative to day of mixing) during the first b
(Mix 1) and second (Mix 2) mixing / moving treatment, per treatment group
Mix Day Treatments P-value
C A B D S.E.D. First mix Second mix Interaction
1 21 to 1 21.3 12.0 0.7 10.3 2.98 ,0.001 NS NS
1 21 to 7 25.5 7.2 3.1 7.9 3.78 0.002 0.086 NS
2 21 to 1 5.6 2.6 26.6 13.9 4.52 0.016 ,0.001 NS
c
2 21 to 5 9.4 13.0 26.1 29.9 – NS ,0.001 NS
a
Data are the average number of wounds or scratches. b
Treatments are: C: No mixing on either occasion, A: mixing at 55 kg, not at 75 kg, B: mixing at 75 kg, not at 55 kg, D: mixing both at 55 kg and at 75 kg.
c
Data were transformed using square root transformation. Back transformed values are presented. S.E.D.s could not be calculated.
4. Discussion
Table 7
The effects of housing system on the change in skin lesions
The present study confirms that mixing unfamiliar
following Mix 1 and Mix 2
pigs results in increased levels of aggression and
Mix Day Kennelled Sloping floor S.E.D. P-value
associated skin lesions. It also suggests that similar
1 21 to 1 6.2 4.8 2.4 NS
levels of aggression may result in different levels of
1 1 to 7 0.3 24.9 2.1 0.017
skin damage, depending on the weight of the pig: skin lesions were more numerous in pigs mixed at 75
2 21 to 1 8.5 16.2 3.6 0.035
a
2 1 to 5 5.1 18.7 – ,0.001 kg, than they were in pigs mixed at 55 kg. However,
a differences between aggressive behaviour
immedi-Data were transformed using square root transformation. Back
ately after mixing, were only found in terms of the
transformed values are presented. S.E.D.s could not be calculated.
frequency of fights and threats, and they were lower
compared to the moving only treatment, but not in after the second mixing treatment compared to the
the unkennelled accommodation (e.g., food conver- first one. It appears that in heavier pigs stocked at the
sion ratio in kennelled building during two weeks same rate, a similar level of aggression (or even a
following Mix 1: 3.7 vs. 2.7 kg intake / kg weight slightly lower level) may result in higher levels of
gain, for mixing1moving vs. moving only; F1,85 skin damage. Possible reasons for this are that
11.8; P50.009). Daily live weight gain between heavier weight pigs apply more force when fighting,
Mix 1 and slaughter did not differ significantly and that at the same stocking density, heavier pigs
between mixing treatments, within housing treat- will occupy more physical space which may block
ments (e.g., daily live weight gain in kennelled escape routes for an animal under attack. The
building: 0.882, 0.842, 0.796 and 0.824 for treat- correlation between the level of fighting in the 2 h
ments C, A, B and D respectively; F3,7751.82; NS). immediately following mixing, and the level of skin
Table 8
Average daily gain per pig (in kg) for mixing treatments following application
Moved Mixed1moved S.E.D. P-value
Two weeks following Mix1
Kennelled 0.916 0.820 0.038 0.015
Sloping floor 0.898 0.919 0.032 NS
Mix2 to slaughter at approximately 85 kg
Kennelled 0.896 0.633 0.070 ,0.001
(8)
damage measured the following day, was very strong Food conversion ratios in the kennelled system
at the end of the finishing period, but not when proved poorer in periods immediately following the
mixing occurred at 55 kg. It is possible that the application of the mixing treatment in groups which
establishment of the social hierarchy is a lengthier had been mixed1moved, compared with groups
process when pigs are mixed for the first time. This which had only been moved. This was associated
would mean that a relatively higher number of fights with slower growth post mixing in these groups.
occur outside the 2 h observation period, resulting in Other studies have also identified an effect of mixing
poorer correlations between immediate behavioural on daily growth rates in the immediate post-mixing
observations and skin damage measured one day period (Waran and Broom, 1993). This effect was
later. not found in the sloping floor system. It is possible
The two housing systems appeared to affect that the different effects of the mixing treatments
mixing induced aggression differently during the two have been caused by differing room temperatures. In
mixing periods. At 55 kg live weight, the unkennel- the sloping floor building an ACNV system was used
led system showed significantly higher levels of a to maintain the temperature around 178C, which
number of aggression parameters. In contrast, fol- effectively meant that the temperature ranged
be-lowing the second mixing treatment higher levels of tween approximately 15 and 198C. The scrape
the frequency of aggressive behaviours was found in through dunging passage in the kennelled building
the kennelled system. There are indications however, was naturally ventilated, resulting in temperatures
that the average duration of fights was shorter in the being very similar to ambient outside temperatures.
kennelled system compared with the sloping floor This study was carried out over the period March to
system. Furthermore, the increase in skin lesions May 1996, with temperatures in the scrape through
during the days following the mixing procedure at dunging passage regularly dropping below 108C. It
Mix 2 are significantly greater in groups housed in has been suggested that subordinate pigs will lie in
the sloping floor system compared with the kennelled less preferred areas of the pen whilst the social
system, although this was reversed and the number hierarchy is being established in the days following
of skin lesions was lower after Mix 1. The most mixing (e.g., Moore et al., 1993; Spoolder, 1998).
likely feature of the kennelled accommodation to Petherick and Baxter (1981) estimate the space
have caused this difference is the physical barrier required for pigs to lie on their sternum to be A
2 0.66
(i.e., the kennel wall) separating the dunging area (m )50.019?W (kg), which would result in a
from the lying area. Effects of barriers on aggression minimum space requirement of approximately 0.27
2 2
in pigs have been suggested by Edwards et al. (1993) m per pig at 55 kg, and 0.33 m at 75 kg. The
2
and Waran and Broom (1993). The authors of these available lying area in the kennel was 3.1 m for 10
papers hypothesise that the barriers help attacked pigs, which during periods of social instability may
pigs to escape out of sight from their attacker. The have been insufficient for all pigs to lie in the kennel
present paper set out to test this hypothesis, by at the same time. Pigs forced to lie outside the
investigating the location of fighting pigs during kennels (particularly over night) may well have
aggressive encounters. It found a very low frequency converted food less efficiently than pigs lying inside
of location changes (lying area to dunging area or the kennels, in order to maintain body temperature.
vice versa) following short interactions such as bites In addition, the stress associated with having to lie in
and threats: the average was less than 1%. Location the least preferred area may have had a metabolic
changes during or immediately following fights were effect on lean tissue synthesis (Spencer, 1985).
far more frequent (on average approximately 35% in Heetkamp et al. (1995), who looked at the energy
mixed1moved groups). However, although trends metabolism of eight-week-old mixed and unmixed
were pointing towards a higher frequency of location pigs, also concluded that ‘‘optimal conditions at the
changes during fighting in the kennelled groups moment of mixing may reduce negative effects on
compared with the sloping floor, the differences were productivity’’. However, in support of the results in
not significant. The data from this experiment there- the present study, they did not identify any long term
fore do not provide conclusive support to the above effects of mixing on live weight. A number of other
(9)
Dingemans, E.C.F.M., Burl«, R.G., Van Putten, G., 1993. The
Sherrit et al., 1974; Greer, 1987). It appears that
influence of rearing conditions on social behaviour of sows in
although mixing may have an immediate effect on
groups [De invloed van opfokomstandigheden op het sociale
productivity if pigs are mixed under suboptimal gedrag van zeugen in groepen. In: IMAG-DLO Report 93-21,
conditions, a limited amount of mixing does not IMAG, Wageningen.
affect overall performance adversely. Edwards, S.A., Mauchline, S., Stewart, A.H., 1993. Designing
pens to minimise aggression when sows are mixed. Farm Build. Progr. 113, 20–23.
Genstat 5 Committee, 1987. Genstat 5 Reference Manual, Oxford
5. Conclusion University Press, Oxford.
Greer, E.B., 1987. Lack of effect of regular movement and of
Mixing finishing pigs in kennelled housing sys- mixing groups on the performance of growing pigs. Aus. J.
Exp. Agric. 27, 217–221.
tems may offer welfare advantages through
modi-Heetkamp, M.J.W., Schrama, J.W., De Jong, L., Swinkels,
fication of agonistic behaviour. However, it may also
J.W.G.M., Schouten, W.G.P., Bosch, M.W., 1995. Energy
me-have detrimental effects on daily live weight gains in tabolism in young pigs as affected by mixing. J. Anim. Sci. 73,
the immediate post mixing period. This may be 3562–3569.
particularly relevant during cold periods if the avail- Luescher, U.A., Friendship, R.M., McKeown, D.B., 1990. Evalua-tion of methods to reduce fighting among regrouped gilts. Can.
able kennel space is insufficient to allow for the
J. Anim. Sci. 70, 363–370.
temporary increase in lying space required, whilst
Martin, P., Bateson, P., 1993. Measuring Behaviour, Cambridge
the social organisation of the group is being re- University Press.
established. Minitab, 1993. Minitab Reference Manual, Sowers Printing
Com-pany, Lebanon.
Moore, A.S., Gonyou, H.W., Ghent, A.W., 1993. Integration of newly introduced and resident sows following grouping. Appl.
Acknowledgements
Anim. Behav. Sci. 38, 257–267.
Olesen, L.S., Nygaard, C.M., Friend, T.H., Bushong, D., Knabe,
ADAS gratefully acknowledges the financial sup- D.A., Vestergaard, K.S., Vaughan, R.K., 1996. Effect of
parti-port it received for this study from the Ministry of tioning pens on aggressive behavior of pigs regrouped at
weaning. Appl. Anim. Behav. Sci. 46, 167–174.
Agriculture Fisheries and Food. We would also like
Petherick, J.C., Baxter, S.H., 1981. Modelling the static spatial
to thank Dr. Tony Lawrence of the University of
requirements of livestock. In: McCormack, J.A.D. (Ed.),
Liverpool for providing visual aids for scoring Modelling, Design and Evaluation of Agricultural Buildings,
stomach lesions, and Mr. Edwin Lunn of Geo. Scottish Farm Buildings Investigation Unit, Aberdeen, pp.
Adams for his expertise and skill in collecting the 75–82.
Sherritt, G.W., Graves, H.B., Gobble, J.L., Hazlett, V.E., 1974.
post-slaughter data. Finally, the work of ADAS
Effects of mixing pigs during the growing–finishing period. J.
Terrington’s technical staff is also gratefully
ack-Anim. Sci. 39, 834–837.
nowledged. Spencer, G.S.G., 1985. Hormonal systems regulating growth. A
review. Livest. Prod. Sci. 12, 31–46.
Spoolder, H.A.M., 1998. Effects of food motivation on stereotypes and aggression in group housed sows. Ph.D. Thesis,
Wagening-References
en Agricultural University, Wageningen.
Tan, S.S.L., Shackleton, D.M., 1990. Effects of mixing unfamiliar Barnett, J.L., Cronin, G.M., McCallum, T.H., Newman, E.A., individuals and of Azaperone on the social behaviour of
1994. Effects of food and time of day on aggression when finishing pigs. Appl. Anim. Behav. Sci. 26, 157–168. grouping unfamiliar adult pigs. Appl. Anim. Behav. Sci. 39, van Putten, G., Burl
«, R.G., 1997. Preparing gilts for group housing 339–347. by increasing their social skills. Appl. Anim. Behav. Sci. 54, Barnett, J.L., Cronin, G.M., McCallum, T.H., Newman, E.A., 173–183.
Hennessy, D.P., 1996. Effects of grouping unfamiliar adult pigs Waran, N.K., Broom, D.M., 1993. The influence of a barrier on after dark, after treatment with amperozide and by using pens the behaviour and growth of early-weaned piglets. Anim. Prod. with stalls, on aggression, skin lesions and plasma cortisol 56, 115–119.
concentrations. Appl. Anim. Behav. Sci. 50, 121–133. Christison, G.I., 1996. Dim light does not reduce fighting or
wounding of newly mixed pigs at weaning. Can. J. Anim. Sci. 76, 141–143.
(1)
2.3.2. Skin damage housing system. Tukey’s HSD was used for pair-Skin damage was assessed on focal animals on the wise comparison of the means of the treatments day before each of the two mixing / moving treat- (Minitab, 1993). Strong tendencies (0.05,P,
ments were applied, on the day after mixing, at day 7 0.10) have also been indicated in the tables. after Mix 1 and on day 5 after Mix 2. The
assess-ment consisted of a count of the number of skin
lesions (bruises, scratches and wounds) per area: 3. Results
front (from snout to middle of back), rear (from
middle of back to tail) and tail. Skin damage was 3.1. Behaviour recorded using the Husky Hunter16 portable
com-puter. The frequency and average duration of a number
of behavioural parameters were higher in groups
2.3.3. Performance which were mixed and moved, compared to groups
All pigs on the experiment were weighed on entry which were only moved (Table 3). However, during to the treatments, at Mix 1, two weeks after Mix 1, at Mix 1 the incidence of minor aggressive interactions Mix 2 (approximately one week before slaughter) such as knocks and threats were higher in the groups and at slaughter. A record was kept of all food added which were moved only, compared to groups which to the single space hoppers in both buildings to give were mixed as well as moved.
total food consumption of the group. From these data There was some indication that the intensity of the the food conversion ratio (FCR), the voluntary food aggressive interactions was greater during Mix 1 intake (VFI), as well as average daily live weight compared with Mix 2. During Mix 1 there was a gain (DLWG) could be calculated. higher frequency of one-sided fights across all four treatments (Mix 1 vs. Mix 2: 0.600 vs. 0.198; 2.4. Statistical analyses F1,18256.81; P50.010), and a higher frequency of knocks / threats (Mix 1 vs. Mix 2: 12.53 vs. 8.41; For the analysis of the behavioural data, the four F1,18257.72; P50.006) compared to Mix 2. randomly chosen focal pigs were the experimental Prior mixing experience did not appear to affect units, with a correction for group effects in the the aggressive behaviour of pigs during the 2 h analyses of variance through blocking (Genstat 5 following a subsequent mix. The only indication that Committee, 1987). The performance data were ana- mixing at 55 kg may have had an effect on behaviour lysed for each separate time period in between during mixing at 75 kg was found in the frequency weighings, and across the whole of the finishing of biting: move (at Mix 1) vs. moving1mixing (at period. As experimental unit the pen was used (when Mix 1): 3.2 vs. 4.8 bites at Mix 2, respectively; comparing within time periods) or the individual F1,8853.3; P50.073.
(when comparing across the whole finishing period, The behaviour of the pigs was affected by the as pen composition changed as a consequence of layout of the pen (Table 4). However, the effects of most treatments). Transformations were used where housing system on aggression immediately post-mix-data did not meet the requirements of the analysis of ing was not the same during Mix 1 and Mix 2. variance in the following order: angular, square root During Mix 1, the incidence of aggressive interac-and logarithmic transformation. Data which could tions and the duration of fights appeared to be lower not be normalised, were analysed using non-paramet- in the K compared with the S treatment. Further-ric techniques. The two treatment factors were more, the average duration of one-sided fights was mixing treatment and housing system. There were no longer in K pens. The frequency of aggression after blocking factors. Interactive effects of mixing treat- the second Mix was greater in the K pens, although ment at 55 kg and mixing just before slaughter were the average duration of two-sided fights was still tested for by using Mix 1 (at 55 kg) and Mix 2 (at longer in the S pens (Table 4).
one week before slaughter) as treatment factors. The percentage of aggressive interactions which These effects were tested for separately for each resulted in a change of location (i.e., a move from
(2)
Table 3
Levels of aggression (per focal pig, per 2-h observation period) and general activity in groups of finishers which were mixed and moved, compared to pigs which were only moved
Behaviour Treatment
Move Mix1move P-value
a a
Mean 95% C.I. Mean 95% C.I.
Mix1
Knock / threat (freq.) 17.1 12.3–22.7 8.7 6.7–10.9 ,0.001
Biting (freq.) 4.2 2.7–6.1 5.8 4.6–7.1 NS
One-sided fights (freq.) 1.5 0.8–2.5 3.2 1.8–5.1 0.030
Two-sided fights (freq.) 2.5 1.5–3.8 2.7 1.4–4.5 NS
b
One-sided fights (av. duration) 16.3 10.9–22.8 14.4 10.0–19.6 NS
b
Two-sided fights (av. duration) 20.0 7.3–54.9 27.6 19.8–38.4 0.094
b
Inactivity (duration) 2887.0 2437–3337 3646.0 3268–4023 0.007
c
Mix2
Knock / threat (freq.) 9.3 7.2–11.6 7.5 5.2–10.2 NS
Biting (freq.) 2.0 1.3–2.9 6.5 4.8–8.4 ,0.001
One-sided fights (freq.) 0.1 0.09–0.14 0.6 0.4–0.9 ,0.001
Two-sided fights (freq.) 0.1 0.08–0.14 3.7 2.6–5.3 ,0.001
b
One-sided fights (av. duration) 14.8 7.6–24.4 14.1 10.4–18.4 NS
b
Two-sided fights (av. duration) 18.0 12.7–25.6 27.1 19.1–38.4 0.060
b
Inactivity (duration) 3343.0 2882–3803 3374.0 2975–3772 NS
a
As most variables had to be transformed prior to analysis, standard errors could not be calculated. The back transformed 95% confidence interval is therefore presented here.
b
All durations are in seconds. c
Please note that at Mix 2 half the groups which were ‘‘mixed and moved’’, had only been ‘‘moved’’ at Mix 1 (i.e., treatment B groups). Conversely, half the groups which were ‘‘moved’’ at Mix 2 had been ‘‘mixed and moved’’ at Mix 1 (treatment A groups).
the kennel into the dunging area or vice versa) was kg appeared to have less skin damage immediately higher immediately after pigs had been mixed and after mixing at 75 kg (day 1 after Mix 2: 15.2 vs. moved compared with pigs which had only been 22.9 lesions per pig for mixing1moving at Mix 1 moved (e.g., one-sided fights: 10.0 vs. 32.5% for vs. moving only at Mix 1; F1,9059.99; P50.004). moved vs. mixed1moved respectively; F1,36513.9; This effect had disappeared five days after the
P,0.001; Table 5). Differences in this parameter second mix. The effects of treatments on changes in between the two housing systems were not signifi- skin lesion scores are presented in Table 6.
cant (e.g., one-sided fights: 26.3 vs. 16.2% for K vs. The increase in skin lesions differed between the S, respectively; F1,3652.83; P50.101). two housing systems. After Mix 1, K pigs had a higher increase in skin lesions between day 21 and
3.2. Skin damage day 7 than S pigs. After Mix 2 this was reversed,
with S pigs showing a greater increase in lesions There was a significant effect of the mixing between days 21 and 1, as well as between days treatment at Mix 1 on the level of skin lesions after 21 and 5 (Table 7).
Mix 1 (e.g., day 1 after Mix 1: 20.3 vs. 12.7 lesions Aggressive behaviour during the first 2 h after Mix per pig for mixing1moving vs. moving only; 1 was not related to the increase in skin lesions
F1,92511.13; P50.001). Similarly, mixing and measured on day 1 after Mix 1, nor was it associated moving (as opposed to moving only) at Mix 2 with changes measured at day 7. Following Mix 2 resulted in a higher number of skin lesions after Mix there was a high degree of correlation between the 2. A significant effect of Mix 1 was found on skin increases in skin damage from day 21 to day 1 and lesions after Mix 2: pigs which had been mixed at 55 the total duration and frequency of two-sided fights
(3)
Table 4
Effects of housing system on duration (in seconds) and frequency of aggressive behaviours per focal pig during the first 2 h after mixing
Behaviour Building
Kennelled Sloping floor P-value
a a
Mean 95% C.I. Mean 95% C.I.
Mix1
Knock / threat (freq.) 10.6 8.3–13.2 15.9 10.9–21.8 0.059
Biting (freq.) 5.9 4.4–7.4 7.0 5.1–8.9 NS
One-sided fights (freq.) 2.2 1.3–3.4 2.3 1.3–3.6 NS
Two-sided fights (freq.) 1.4 0.8–2.2 4.5 2.9–6.4 ,0.001
b
One-sided fights (av. duration) 12.0 7.9–16.9 19.5 11.8–29.2 0.003
b
Two-sided fights (av. duration) 3.0 1.1–8.5 3.3 1.4–7.6 NS
b
Inactivity (duration) 3154.0 2766–3541 3402.0 2901–3902 NS
Mix2
Knock / threat (freq.) 12.3 9.3–15.8 5.3 4.2–6.5 ,0.001
Biting (freq.) 3.9 2.8–5.2 4.0 2.6–5.8 NS
One-sided fights (freq.) 0.3 0.1–0.7 0.1 0.0–0.2 0.092
Two-sided fights (freq.) 1.1 0.5–2.3 0.4 0.2–1.0 0.053
b
One-sided fights (av. duration) 15.6 10.7–21.5 12.9 8.5–18.2 NS
b
Two-sided fights (av. duration) 16.6 11.8–23.5 36.5 26.2–50.8 ,0.001 b
Inactivity (duration) 3400.0 2986–3813 3273.0 2819–3726 NS
a
As most variables had to be transformed prior to analysis, standard errors could not be calculated. The back transformed 95% confidence interval is therefore presented here.
b
All durations are in seconds. Table 5
Percentage of interactions which resulted in a change of location (lying area vs. dunging area) for one or both of the animals involved Behaviour Building
Kennelled Sloping floor P-value
Moved Mixed Moved Mixed S.E.D. Housing Mixed Interact.
a
Knock / threat 0.16 0.41 0.15 0.20 – NS NS NS
a
Biting 0.09 0.45 0.03 0.79 – NS 0.009 NS
One-sided fights 17.0 35.7 3.0 29.3 8.6 NS ,0.001 NS
Two-sided fights 13.4 32.0 11.1 42.1 5.5 NS ,0.001 NS
a e
An log transformation had to be used prior to data analysis. Means are back transformed values. S.E.D.s could not be calculated.
during the first 2 h after mixing and moving (e.g., ing. In the kennelled building, both after Mix 1 and correlation between total duration of two-sided fights after Mix 2, DLWG was lower in the groups which and skin lesion score: r50.620; n596; P,0.001). were mixed compared to the groups which had only No such relationship was found between skin lesions been moved. No such effect was found in the sloping at day 1 and other behavioural variables such as floor building (see Table 8). In both buildings biting and knocks or threats. however, food intakes did not differ in the periods immediately following mixing (e.g., food intake in
3.3. Performance kennelled building during two weeks following Mix
1: 2.42 vs. 2.46 kg per day, for mixing1moving vs. Treatment effects on daily live weight gain ap- moving only; F1,850.28; NS). As a result food peared to differ between the two housing systems, conversion ratios were poorer under the mixing1
(4)
Table 6 a
Increase in levels of skin damage recorded between days 21 and 1, and days21 and 7 or 5 (all relative to day of mixing) during the first b
(Mix 1) and second (Mix 2) mixing / moving treatment, per treatment group
Mix Day Treatments P-value
C A B D S.E.D. First mix Second mix Interaction
1 21 to 1 21.3 12.0 0.7 10.3 2.98 ,0.001 NS NS
1 21 to 7 25.5 7.2 3.1 7.9 3.78 0.002 0.086 NS
2 21 to 1 5.6 2.6 26.6 13.9 4.52 0.016 ,0.001 NS
c
2 21 to 5 9.4 13.0 26.1 29.9 – NS ,0.001 NS
a
Data are the average number of wounds or scratches. b
Treatments are: C: No mixing on either occasion, A: mixing at 55 kg, not at 75 kg, B: mixing at 75 kg, not at 55 kg, D: mixing both at 55 kg and at 75 kg.
c
Data were transformed using square root transformation. Back transformed values are presented. S.E.D.s could not be calculated. 4. Discussion
Table 7
The effects of housing system on the change in skin lesions
The present study confirms that mixing unfamiliar
following Mix 1 and Mix 2
pigs results in increased levels of aggression and
Mix Day Kennelled Sloping floor S.E.D. P-value
associated skin lesions. It also suggests that similar
1 21 to 1 6.2 4.8 2.4 NS
levels of aggression may result in different levels of
1 1 to 7 0.3 24.9 2.1 0.017
skin damage, depending on the weight of the pig: skin lesions were more numerous in pigs mixed at 75
2 21 to 1 8.5 16.2 3.6 0.035
a
2 1 to 5 5.1 18.7 – ,0.001 kg, than they were in pigs mixed at 55 kg. However,
a differences between aggressive behaviour
immedi-Data were transformed using square root transformation. Back
ately after mixing, were only found in terms of the
transformed values are presented. S.E.D.s could not be calculated.
frequency of fights and threats, and they were lower compared to the moving only treatment, but not in after the second mixing treatment compared to the the unkennelled accommodation (e.g., food conver- first one. It appears that in heavier pigs stocked at the sion ratio in kennelled building during two weeks same rate, a similar level of aggression (or even a following Mix 1: 3.7 vs. 2.7 kg intake / kg weight slightly lower level) may result in higher levels of gain, for mixing1moving vs. moving only; F1,85 skin damage. Possible reasons for this are that 11.8; P50.009). Daily live weight gain between heavier weight pigs apply more force when fighting, Mix 1 and slaughter did not differ significantly and that at the same stocking density, heavier pigs between mixing treatments, within housing treat- will occupy more physical space which may block ments (e.g., daily live weight gain in kennelled escape routes for an animal under attack. The building: 0.882, 0.842, 0.796 and 0.824 for treat- correlation between the level of fighting in the 2 h ments C, A, B and D respectively; F3,7751.82; NS). immediately following mixing, and the level of skin
Table 8
Average daily gain per pig (in kg) for mixing treatments following application
Moved Mixed1moved S.E.D. P-value
Two weeks following Mix1
Kennelled 0.916 0.820 0.038 0.015
Sloping floor 0.898 0.919 0.032 NS
Mix2 to slaughter at approximately 85 kg
Kennelled 0.896 0.633 0.070 ,0.001
(5)
damage measured the following day, was very strong Food conversion ratios in the kennelled system at the end of the finishing period, but not when proved poorer in periods immediately following the mixing occurred at 55 kg. It is possible that the application of the mixing treatment in groups which establishment of the social hierarchy is a lengthier had been mixed1moved, compared with groups process when pigs are mixed for the first time. This which had only been moved. This was associated would mean that a relatively higher number of fights with slower growth post mixing in these groups. occur outside the 2 h observation period, resulting in Other studies have also identified an effect of mixing poorer correlations between immediate behavioural on daily growth rates in the immediate post-mixing observations and skin damage measured one day period (Waran and Broom, 1993). This effect was
later. not found in the sloping floor system. It is possible
The two housing systems appeared to affect that the different effects of the mixing treatments mixing induced aggression differently during the two have been caused by differing room temperatures. In mixing periods. At 55 kg live weight, the unkennel- the sloping floor building an ACNV system was used led system showed significantly higher levels of a to maintain the temperature around 178C, which number of aggression parameters. In contrast, fol- effectively meant that the temperature ranged be-lowing the second mixing treatment higher levels of tween approximately 15 and 198C. The scrape the frequency of aggressive behaviours was found in through dunging passage in the kennelled building the kennelled system. There are indications however, was naturally ventilated, resulting in temperatures that the average duration of fights was shorter in the being very similar to ambient outside temperatures. kennelled system compared with the sloping floor This study was carried out over the period March to system. Furthermore, the increase in skin lesions May 1996, with temperatures in the scrape through during the days following the mixing procedure at dunging passage regularly dropping below 108C. It Mix 2 are significantly greater in groups housed in has been suggested that subordinate pigs will lie in the sloping floor system compared with the kennelled less preferred areas of the pen whilst the social system, although this was reversed and the number hierarchy is being established in the days following of skin lesions was lower after Mix 1. The most mixing (e.g., Moore et al., 1993; Spoolder, 1998). likely feature of the kennelled accommodation to Petherick and Baxter (1981) estimate the space have caused this difference is the physical barrier required for pigs to lie on their sternum to be A
2 0.66
(i.e., the kennel wall) separating the dunging area (m )50.019?W (kg), which would result in a from the lying area. Effects of barriers on aggression minimum space requirement of approximately 0.27
2 2
in pigs have been suggested by Edwards et al. (1993) m per pig at 55 kg, and 0.33 m at 75 kg. The
2
and Waran and Broom (1993). The authors of these available lying area in the kennel was 3.1 m for 10 papers hypothesise that the barriers help attacked pigs, which during periods of social instability may pigs to escape out of sight from their attacker. The have been insufficient for all pigs to lie in the kennel present paper set out to test this hypothesis, by at the same time. Pigs forced to lie outside the investigating the location of fighting pigs during kennels (particularly over night) may well have aggressive encounters. It found a very low frequency converted food less efficiently than pigs lying inside of location changes (lying area to dunging area or the kennels, in order to maintain body temperature. vice versa) following short interactions such as bites In addition, the stress associated with having to lie in and threats: the average was less than 1%. Location the least preferred area may have had a metabolic changes during or immediately following fights were effect on lean tissue synthesis (Spencer, 1985). far more frequent (on average approximately 35% in Heetkamp et al. (1995), who looked at the energy mixed1moved groups). However, although trends metabolism of eight-week-old mixed and unmixed were pointing towards a higher frequency of location pigs, also concluded that ‘‘optimal conditions at the changes during fighting in the kennelled groups moment of mixing may reduce negative effects on compared with the sloping floor, the differences were productivity’’. However, in support of the results in not significant. The data from this experiment there- the present study, they did not identify any long term fore do not provide conclusive support to the above effects of mixing on live weight. A number of other
(6)
Dingemans, E.C.F.M., Burl«, R.G., Van Putten, G., 1993. The Sherrit et al., 1974; Greer, 1987). It appears that
influence of rearing conditions on social behaviour of sows in
although mixing may have an immediate effect on
groups [De invloed van opfokomstandigheden op het sociale
productivity if pigs are mixed under suboptimal gedrag van zeugen in groepen. In: IMAG-DLO Report 93-21, conditions, a limited amount of mixing does not IMAG, Wageningen.
affect overall performance adversely. Edwards, S.A., Mauchline, S., Stewart, A.H., 1993. Designing pens to minimise aggression when sows are mixed. Farm Build. Progr. 113, 20–23.
Genstat 5 Committee, 1987. Genstat 5 Reference Manual, Oxford 5. Conclusion University Press, Oxford.
Greer, E.B., 1987. Lack of effect of regular movement and of
Mixing finishing pigs in kennelled housing sys- mixing groups on the performance of growing pigs. Aus. J. Exp. Agric. 27, 217–221.
tems may offer welfare advantages through
modi-Heetkamp, M.J.W., Schrama, J.W., De Jong, L., Swinkels,
fication of agonistic behaviour. However, it may also
J.W.G.M., Schouten, W.G.P., Bosch, M.W., 1995. Energy
me-have detrimental effects on daily live weight gains in tabolism in young pigs as affected by mixing. J. Anim. Sci. 73, the immediate post mixing period. This may be 3562–3569.
particularly relevant during cold periods if the avail- Luescher, U.A., Friendship, R.M., McKeown, D.B., 1990. Evalua-tion of methods to reduce fighting among regrouped gilts. Can.
able kennel space is insufficient to allow for the
J. Anim. Sci. 70, 363–370.
temporary increase in lying space required, whilst
Martin, P., Bateson, P., 1993. Measuring Behaviour, Cambridge
the social organisation of the group is being re- University Press.
established. Minitab, 1993. Minitab Reference Manual, Sowers Printing
Com-pany, Lebanon.
Moore, A.S., Gonyou, H.W., Ghent, A.W., 1993. Integration of newly introduced and resident sows following grouping. Appl. Acknowledgements
Anim. Behav. Sci. 38, 257–267.
Olesen, L.S., Nygaard, C.M., Friend, T.H., Bushong, D., Knabe,
ADAS gratefully acknowledges the financial sup- D.A., Vestergaard, K.S., Vaughan, R.K., 1996. Effect of
parti-port it received for this study from the Ministry of tioning pens on aggressive behavior of pigs regrouped at weaning. Appl. Anim. Behav. Sci. 46, 167–174.
Agriculture Fisheries and Food. We would also like
Petherick, J.C., Baxter, S.H., 1981. Modelling the static spatial
to thank Dr. Tony Lawrence of the University of
requirements of livestock. In: McCormack, J.A.D. (Ed.),
Liverpool for providing visual aids for scoring Modelling, Design and Evaluation of Agricultural Buildings, stomach lesions, and Mr. Edwin Lunn of Geo. Scottish Farm Buildings Investigation Unit, Aberdeen, pp.
Adams for his expertise and skill in collecting the 75–82.
Sherritt, G.W., Graves, H.B., Gobble, J.L., Hazlett, V.E., 1974.
post-slaughter data. Finally, the work of ADAS
Effects of mixing pigs during the growing–finishing period. J.
Terrington’s technical staff is also gratefully
ack-Anim. Sci. 39, 834–837.
nowledged. Spencer, G.S.G., 1985. Hormonal systems regulating growth. A
review. Livest. Prod. Sci. 12, 31–46.
Spoolder, H.A.M., 1998. Effects of food motivation on stereotypes and aggression in group housed sows. Ph.D. Thesis, Wagening-References
en Agricultural University, Wageningen.
Tan, S.S.L., Shackleton, D.M., 1990. Effects of mixing unfamiliar Barnett, J.L., Cronin, G.M., McCallum, T.H., Newman, E.A., individuals and of Azaperone on the social behaviour of
1994. Effects of food and time of day on aggression when finishing pigs. Appl. Anim. Behav. Sci. 26, 157–168. grouping unfamiliar adult pigs. Appl. Anim. Behav. Sci. 39, van Putten, G., Burl
«, R.G., 1997. Preparing gilts for group housing
339–347. by increasing their social skills. Appl. Anim. Behav. Sci. 54, Barnett, J.L., Cronin, G.M., McCallum, T.H., Newman, E.A., 173–183.
Hennessy, D.P., 1996. Effects of grouping unfamiliar adult pigs Waran, N.K., Broom, D.M., 1993. The influence of a barrier on after dark, after treatment with amperozide and by using pens the behaviour and growth of early-weaned piglets. Anim. Prod. with stalls, on aggression, skin lesions and plasma cortisol 56, 115–119.
concentrations. Appl. Anim. Behav. Sci. 50, 121–133. Christison, G.I., 1996. Dim light does not reduce fighting or
wounding of newly mixed pigs at weaning. Can. J. Anim. Sci. 76, 141–143.