Agriculture Reference
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did differ from the stall treatment: they were less often rebred within 10 d after weaning
compared with stalled sows (88.8 vs. 96.6%).
Other studies did not show any effect of timing at grouping. Van Wettere
et al.
(2008)
compared gilts that were not mixed (but remained in their pre-mating group), or that
were mixed at either d 3-4 or d 8-9 of pregnancy. They saw no differences in pregnancy
rate or embryo survival. Likewise, Cassar
et al.
(2008) introduced 617 sows to groups of
15 at d 2, 7, 14, 21 or 28 after service and found no effects on farrowing rates or litter size.
It appears that studies looking into the timing of mixing contradict each other. Furthermore,
attempts to identify any direct relationship between early embryonic development and
stress to the sow have thus far also failed. Soede
et al.
(2007) assigned 81 cyclic gilts to
different stress related treatments, namely, stress treatment during the follicular phase
(n=20), stress treatment during early pregnancy (n=20), stress treatment during both
phases (n=21), and no stress treatment (n=20). They investigated stress parameters such
as heart rate, cortisol concentrations, stereotypic behaviour, embryonic development,
and other reproductive parameters. Their results do not suggest any effect of repeatedly
applied acute stressors on the chronic stress-response during the follicular phase and
early pregnancy in gilts, nor did they observe any effect on reproductive processes.
It is therefore likely that other factors related with the group housing system or the type
of sows used influence the effects of timing of grouping on subsequent reproductive
performance. Nevertheless, it seems wise to avoid stressful events in early pregnancy,
especially in weeks 2-3 following insemination, to avoid a decrease in productivity.
Space allowance
All animals need space to rest, eat, defecate but also to perform social behaviours and
to satisfy their intrinsic motivation to explore the environment. Grouping sows in a
situation where there is insufficient space will increase the adverse consequences of
aggressive behaviours and induce chronically elevated cortisol levels. Several studies
reported decreased aggression and injuries when increasing space allowance (Barnett
et al.
, 2001; Docking
et al.
, 2000; Remience
et al.
, 2008). It is likely that this is mainly
due to reduced opportunities to avoid aggression, e.g. by showing submissive behaviour
(Jensen, 1982). Insufficient space allowance in group-housed sows can also induce greater
incidences of feet and leg injuries, which may have been inflicted by contact with pen
fittings or flooring, or by non-agonistic interactions between individuals such as gilts
stepping on one another (Harris
et al.
, 2006).
The minimum space allowance needed to provide sufficient welfare to sows has not been
determined scientifically yet. As a starting point for further quantification, EFSA (2005)
described three types of space required: static space, behavioural space and interaction
space. Static space is the easiest one to estimate, as it can be demonstrated that for pigs
to simply lie or stand the equation A=k×W
0.666
should be used. In this equation A is the
area in m
2
, W is body weight in kg and k is a constant depending on the posture of the
animal (Baxter, 1986). For a sternal lying or standing pig k=0.019, and for recumbent
