Behavioral Genetics in Pigs and Relations to Welfare - Genetics and the Behavior of Domestic Animals - page 411

to the greater surface to body mass ratio resulting in higher heat losses. Nest
building is a heritable trait in mice ( Lynch, 1980 ).
The duration of farrowing influences piglet survival and the risk of dying
during or shortly after farrowing is greater for piglets born late ( Canario et al.,
2009 ). Farrowing duration is therefore a potential selection trait, but it is very
difficult to record on a large scale. For a proper assessment, the observer
should stay beside the sow and at the same time avoid disturbing the farrow-
ing. There is a genetic variation in farrowing duration (but the heritability is
low when recorded in nucleus herds; h 2

0.1) and it is correlated with litter
size and number of stillborn ( Holm et al., 2004 ). No genetic relationships
between farrowing duration and behavior are reported in the literature.
Sows are sometimes aggressive towards their newborn piglets. Infanticide
(also called savaging) is associated with endocrine changes during farrowing,
farrowing experience, environment, and genotype. The heritability for
savaging piglets is high, but it is a tricky trait to analyze and the range of
heritability estimates is large (h 2

#

0.9; Knap and Merks, 1987; Van der
Steen et al., 1988 ). Although rarely included in the genetic evaluation, there
is an ongoing selection against this trait at the farm level. Besides, natural
selection helps the breeders; often there are no piglets alive to select in
affected litters. Single genes with a large influence on this defect have been
found and many of them seem to interact. Several QTL have been detected
on different chromosomes, among which a promising QTL on the X chromo-
some has been found in a Large White Duroc

5 0.1

Erhualian population ( Chen
et al., 2009b ). Some QTL regions found in pigs have corresponding regions
in humans and rodents that harbor genes controlling anxiety, bipolar disor-
der, or coping behavior ( Quilter et al., 2007 ), and some mitochondrial genes
are differentially expressed when savaging and not savaging sows are com-
pared. This is interesting because the mitochondria contain DNA that is
inherited solely through the mother. Several of these genes are related to
neural pathways.
Crushing by the sow is one of the most common causes of piglet mortal-
ity. The introduction of farrowing crates was primarily aimed at reducing
crushing. Crates also facilitate good hygiene and protect the farmer from
aggressive sows. There is growing contest against this production system
which induces higher stress in sows as compared to farrowing pens without
crates ( Jarvis et al., 1997 ). In a recent EFSA report, the experts recom-
mended that

3

... the use of loose farrowing systems should be considered as a serious alternative
to conventional crated systems, as good performance results can be obtained in such
systems if sows are kept in sufficiently large pens.

Spoolder et al., 2011

Since the crate is very stressful for the sow, we must use alternative ways
to prevent crushing, such as selection for improved maternal behavior.