Agriculture Reference
In-Depth Information
highlights the complexity of farming systems.
Providing pigs with straw is an example where
animal welfare and improvements in environ-
mental sustainability can go hand in hand.
Straw has been shown to be advantageous for
growing pigs in a number of ways (Tuyttens,
2005); its use improves thermal comfort while
lying and provides opportunities for exploration,
rooting, foraging and chewing. Providing alter-
natives for pigs to engage in oral activities are
important to prevent injurious behaviours such
as tail biting (reviewed by Schrøder-Petersen
and Simonsen, 2001; Taylor
et al
., 2010).
However, there are practical constraints associ-
ated with incorporating straw into intensive sys-
tems, as the manure handling system must be
compatible. One alternative housing system, the
Straw-Flow system, contains two distinct areas,
one area for lying and oral activities that con-
tains straw and another, strawless area for
excreta. This system capitalizes on the willing-
ness of pigs to use a dunging area that can be
frequently cleaned. Pigs kept in the Straw-Flow
system show behavioural changes consistent
with improved animal welfare (e.g. less pig-
directed oral behaviour; Kelly
et al
., 2000).
Greenhouse gas emissions (CH
4
, N
2
O, NH
3
) are
also lower in Straw-Flow systems, compared
with reference values for forced ventilated, fully
slatted (thus strawless) floor systems (Amon
et al
., 2007). Thus, in this type of system, animal
welfare and environmental sustainability are
both improved by the addition of straw in this
housing design. Moreover, Bornett
et al
. (2003)
argued that that adding straw only provides
a modest increase in cost (7%), indicating that
economic sustainability (at least in the UK) may
also correspond in this situation.
This relationship is not always so straightfor-
ward. As discussed above, one specific animal
welfare concern expressed by the public is ani-
mals that are kept under 'unnatural' conditions
with limited space and often a limited ability to
engage in social interactions and other natural
behaviours (Fraser
et al
., 1997). The problem
with environments where animals are prevented
from being able to stretch their wings or limbs or
turn around freely can only be addressed by less
restrictive housing, such as group housing sys-
tems for gestating sows or more space for lay-
ing hens. Sow housing provides an example of
how complex comparisons between intensive
and less restrictive systems can be from a welfare
and environmental perspective.
Sows are often housed in gestation stalls for
most of the duration of their 4-month pregnan-
cies and in farrowing crates, where they give
birth to their young (Fraser
et al
., 2001). By
design, these types of housing reduce the chal-
lenges associated with aggression between sows
during gestation and crushing or savaging of
newborn piglets at farrowing, both important
welfare concerns. However, these forms of
restrictive housing place limitations on freedom
of movement. It is estimated that 92% of sows in
these systems of confinement exhibit oral stereo-
typies, which are abnormal behaviours associ-
ated with confinement (Mason and Rushen,
2006). In contrast, outdoor housing allows sows
a high degree of freedom of movement (Hötzel
et al
., 2004) and the ability to express a larger
repertoire of natural behaviours that they are
highly motivated to perform, such as rooting and
nesting behaviour (e.g. Špinka, 2006). Outdoor
housing systems for sows were previously criti-
cized for having higher rates of neonatal mor-
tality (Ngapo
et al
., 2004), but current estimates
of live-born mortality in the UK are similar for
outdoor-housed sows (10.5%) and indoor-housed
sows (11.8%, Meat and Livestock Commission,
2006). Despite the welfare benefits of outdoor
systems, there are a number of environmental
implications of this type of housing (reviewed by
Siegford
et al
., 2008). An obvious limitation is
weather and exposure to fluctuations in environ-
mental temperature (Akos and Bilkei, 2004).
Outdoor systems are only viable in regions that
do not have extreme weather and, even then,
may not be as efficient as indoor housing, in
terms of environmental impact. For example,
nitrogen and phosphorus surpluses are highest
on Danish farms that keep sows outside (Nielsen
and Kristensen, 2005), although management
and stocking density likely affect the degree of
this problem (Williams
et al
., 2000). More inten-
sive housing systems also face challenges with
nitrogen containment (e.g. Karr
et al
., 2001),
but non-point sources of contamination may be
more difficult to control in outdoor systems
than in more intensive ones. There are also con-
cerns about land use associated with outdoor
housing systems for sows. Namely, more space
is needed for these systems and allowing pigs to
root reduces pasture cover and can intensify
