H .A.M. Spoolder et al. Livestock Production Science 63 2000 121 –129
127 Table 6
a
Increase in levels of skin damage recorded between days 2 1 and 1, and days 2 1 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
2 1 to 1 2 1.3
12.0 0.7
10.3 2.98
, 0.001 NS
NS 1
2 1 to 7 2 5.5
7.2 3.1
7.9 3.78
0.002 0.086
NS 2
2 1 to 1 5.6
2.6 26.6
13.9 4.52
0.016 , 0.001
NS
c
2 2 1 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 2 1 to 1 6.2
4.8 2.4
NS
levels of aggression may result in different levels of
1 1 to 7
0.3 2 4.9
2.1 0.017
skin damage, depending on the weight of the pig: skin lesions were more numerous in pigs mixed at 75
2 2 1 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 mixing
1 moving vs. moving only; F 5
skin damage. Possible reasons for this are that
1,8
11.8; P 5 0.009. 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; F
5 1.82; NS. immediately following mixing, and the level of skin
3,77
Table 8 Average daily gain per pig in kg for mixing treatments following application
Moved Mixed
1 moved S.E.D.
P-value Two weeks following Mix
1 Kennelled
0.916 0.820
0.038 0.015
Sloping floor 0.898
0.919 0.032
NS Mix
2 to slaughter at approximately 85 kg Kennelled
0.896 0.633
0.070 , 0.001
Sloping floor 0.698
0.692 0.074
NS
128 H
.A.M. Spoolder et al. Livestock Production Science 63 2000 121 –129
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 mixed
1 moved, 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 17 8C, 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 19
8C. 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 10 8C. 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
5 0.019 ? 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
mixed 1 moved 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 hypothesis.
studies also failed to find a long term effect e.g.,
H .A.M. Spoolder et al. Livestock Production Science 63 2000 121 –129
129 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
