Agriculture Reference
In-Depth Information
Purely based on scientific evidence it does not seem possible to conclude either in favour
or against group housing of dry sows. Fraser (2003) suggested that this may be due to the
fact that different views exist on how the welfare of animals should be evaluated in terms
of: (1) biological functioning; (2) the absence of suffering; or (3) the naturalness of their
husbandry situation. He stated that 'when attempting to assess animal welfare, different
scientists select diferent criteria, relecting one or more of these value-dependent views.
Weaver and Morris (2004) confirmed this view and proposed in their New Zealand
perspective on sow stalls that science will not determine which of the two approaches
is best (group or individual housing). Instead, they encouraged an ethical debate based
on scientific inputs, a view shared by others who argue that in some countries the status
quo regarding individual housing is maintained 'pending irrefutable evidence in favour
of change' (Caulfield and Cambridge, 2008).
Science may not be leading the discussion anymore on whether pregnant sows should
be kept in groups or individually, and perhaps it never really was. The public debate,
in particular in Europe, has persuaded societies to adopt legislation in favour of group
housing. In addition, it is persuading large companies to change the way in which they
breed pigs (Mench, 2008), and retailers to sell pork from companies that implement these
changes. Millions of sows around the world are currently kept in groups and provide an
income to their owners. The important scientific question which remains is how this can
be done in a way that will optimize sow welfare and farm productivity. The following
paragraphs summarise the current knowledge on this question.
3.2
Sow social behaviour in group-housing systems
Successful sow husbandry results in high productivity, good sow welfare and a pleasant
working environment for farm staff. A crucial difference between individual and group-
housing systems which affects all of these aspects is that in group housing sows can
interact with each other, leading to an increase in both positive as well as negative social
interactions. Aggression between sows constitutes the most prominent form of negative
social interaction. It affects sow health and welfare, the farm's productivity and (as a
consequence of both) the level of job satisfaction of those who work with the animals.
Fighting is detrimental to the welfare of the animals involved. The losing animal generally
suffers most, possibly sustaining severe skin damage, abscesses, locomotion problems
(Burfoot
et al.
,
1995; Svendsen
et al.
,
1990;) and acute psychological stress resulting in
an increase in heart rate (Marchant
et al.
, 2001) and cortisol levels (Mendl
et al.
,
1992)
during and after the fight. In addition, there are indications that social stress during the
early stages of pregnancy may result in decreased fertility (Bokma, 1990; Burfoot
et al.
,
1997), whereas aggression incurred at weaning reduces the expression of subsequent
oestrus behaviour (Pedersen
et al.
, 1993). In situations were available resources are
limited, lower ranking animals may fail to cope with their social environment entirely
and suffer severe weight loss or, in extreme cases, death.
