Behavioral Genetics in Pigs and Relations to Welfare - Genetics and the Behavior of Domestic Animals - page 404

( Keeling et al., 2012 ). Is selection against tail biting possible, as a comple-
ment to environmental improvements?
The Royal Society for the Prevention of Cruelty to Animals, which is the
organization behind “Freedom food”, knows that tail biting has a genetic
background. They write on their home page that “the genetics of the pigs on
a unit can affect the likelihood of tail biting occurring” ( RSPCA, 2012 ). But
it is a difficult trait to study because it is hard to identify the biter. Breuer
et al. (2005) defined biters as pigs involved in more than 50% of the tail-
biting incidences within 10 minutes of observation. Tail biting is not per-
formed by all pigs, almost 90% are never observed to perform tail bites
( Brunberg et al., 2011 ).
Breed differences in the tendency to tail-bite group mates have been
found by Breuer et al. (2003) . Nordic studies show that Landrace and Duroc
pigs tail-bite more often than Yorkshire and Hampshire pigs. Yorkshire pigs
are tail-bitten more often whereas Hampshire pigs are tail-bitten less often
than the other breeds ( Sinisalo et al., 2012; Westin, 2000 ). However, Lund
and Simonsen (2000) found no clear breed effect. The genetic influence on
this behavior can be more relevant within than between breeds.
Around 3% of the pigs in the study of Breuer et al. (2005) were classified
as biters. The heritability of this “yes or no trait” was estimated at 0.3 (after
transformation to an underlying continuous scale) in Landrace pigs. The cor-
responding heritability was zero in Large White pigs. At the genetic level,
tail biting is unfavorably correlated with growth rate and leanness. A
genome-wide association study was done on records of tail biting from
Norwegian farms. The first results showed that different chromosomal
regions on the pig genome are associated with the delivery and receipt of
tail-biting behaviors ( Wilson et al., 2012 ).
To get a better understanding of the molecular mechanisms of tail biting,
Emma Brunberg studied gene expression in the brain (hypothalamus and pre-
frontal cortex) in her PhD project ( Brunberg, 2011 ). She used pigs from a
Finnish herd and analyzed the abundance of RNA molecules from specific
genes. There were differences in gene expression between biters and victims
and also between these types and neutral pigs not involved in tail biting
although they were housed together with biters. Many of the genes differed
between neutral pigs and the other categories. The EGF gene that codes for
an epidermal growth factor and has an important function in the dopaminer-
gic system was less expressed in neutral pigs. This gene is involved in
novelty-seeking in humans ( Keltikangas-J ¨ rvinen et al., 2006 ). Furthermore,
the GTF2I gene which is involved in sociability is up-regulated in the hypo-
thalamus of neutral pigs. Also, the GHRL gene which codes for a hormone
related to appetite and the PDK4 gene related to fat content were up-
regulated in these pigs. The results give further grounds to the suspicion that
selection for high production is followed by some abnormal behaviors
directed towards group mates.