Agriculture Reference
In-Depth Information
Most of the lesions caused by aggression are scratches or cuts on the skin. In sows and
gilts the vulva is an occasional target. However, vulva biting is not regarded as an act of
aggression but rather as one of frustration caused, for example, by lack of access to feed.
Aggression may also result in leg problems, in particular when the design of the pen is
such that animals cannot easily avoid an incident (through space limitations) or when
the floor provides insufficient support to the claws during an interaction (too slippery
or poor quality slats). The incidence of leg problems as a consequence of fighting is
substantially lower than that of skin lesions. Finally, aggression is inevitably associated
with physiological and psychological stress (see above), although it may not necessarily
affect reproductive performance. Couret
et al.
(2009) repeatedly applied social stress
to pregnant gilts during the last third of gestation and found that although this was
associated with repeated activation of the hypothalamo-pituitary-adrenal axis, it did not
impair their immune function and pregnancy outcome. Soede
et al.
(2007) had previously
obtained similar results.
3.2.1
Reducing negative social interactions
Competition for access to a limited resource and the establishment of a social relationship
between unfamiliar animals are the two main reasons for sows to engage in fighting. They
differ considerably in a number of ways. Aggression related to competition for access to
food, water or a place to lie down is generally short in duration, but very frequent (often
daily). Social relationships, on the other hand, are established when unfamiliar animals
are mixed and need to determine their relative ranking in the pecking order. This type of
aggression is not as frequent, but can be much more intense.
Establishing a dominance hierarchy
Being a high ranking sow has more advantages than simply being the first one to get
access to resources such as feed, water and a preferred lying space. Hoy
et al.
(2009b)
reported that sows with a high ranking position had a greater litter size of total born
piglets on the two farms they studied (12.66 and 16.14 piglets per litter for these farms)
than the low-ranking group-mates (12.13 and 14.83 piglets/litter respectively). Tönepöhl
et al.
(2013) added that while sows recorded frequently as aggressors post-mixing gave
birth to more total and live born piglets, sows with higher skin lesion scores had a lower
reproductive performance (e.g. skin lesion score front vs. total born piglets: r=-0.28,
P
<0.01). These effects on reproductive performance may be related to stress associated
with a state of 'predictability' or a degree of being 'in control.
Although fighting between sows potentially has quite serious consequences, the social
hierarchy is usually established within two days after introduction of new animals,
resulting in a dramatic decrease in aggression (Bokma and Kersjes, 1988; Luescher
et al.
,
1990). Full integration of new sows in a resident group takes a lot longer. Moore
et al.
(1993) and Spoolder
et al.
(1998) studied small groups of gilts or sows introduced to large
dynamic groups and estimated integration to take at least 3-4 weeks. In this comparatively
stable period the relative social position of individuals was confirmed, facilitating the
organisation of the whole group, for example through the development of feeding orders
