Behavioral Genetics in Pigs and Relations to Welfare - Genetics and the Behavior of Domestic Animals - page 409

familiarity rather than genetic relatedness and they are not able to recognize
relatives if they have not been raised together ( Bekoff, 1981 ). Are there
“helpful” pigs, and if so, why? Natural selection would result in selfish indi-
viduals that are successful at the expense of others, not in successful groups.
This is observed, e.g., in wild plants which compete for light, but breeding is
not equal to natural selection. Maybe “helpful” pigs are merely pigs not dis-
turbing other pigs? Pigs genetically predisposed for eating and staying calm
without spending time and energy on bothering group mates would get high
breeding values for own growth and for pen mates' growth. That strategy is
probably only successful if feed is not a limited resource.
It would be interesting to study how general the breeding values for
social effects are in different environments with more or less limited
resources. With a group size ranging from five to 15 animals per pen, the
social genetic effects were diluted in larger groups ( Canario et al., 2010 ).
Turner et al. (2001) suggest that in very large groups, social strategies
depend more and more on no social rules. It can be assumed that the behav-
ioral response to selection for growth will be quite different with different
pen and group size and different feeding systems.

Aggressive Behavior in Sows
Sows that have been housed in farrowing pens fight during the first 24 hours
after weaning, when mixed with other sows. Sows should be loose housed
for welfare reasons but fighting can be detrimental for low-ranked sows.
FAWC's report on the Welfare Implications of Animal Breeding and
Breeding Technologies in Commercial Agriculture (2004) state that:

FAWC is aware that selection for temperament is becoming increasingly important
... for species such as pigs and laying hens where a move away from close
confinement systems, driven by either legislation or market forces, has revealed the
importance of behavioral traits such as reduced levels of aggression.

It would be interesting to use the group model on loose-housed sows, to
estimate direct and social effects on reproduction traits like interval from
weaning to estrus and pregnancy rate.
In a Danish field study of pregnant sows, all aggressive interactions dur-
ing the first 30 minutes after mixing were recorded ( L¨vendahl et al., 2005 ).
The identity of sows delivering and receiving attacks were noted. The model
included two genetic effects, one describing the capacity to attack and the
other describing the predisposal for being attacked. Repeated measures from
all dyads (all pairs) of sows in the pen were analyzed. Performing aggressive
behavior was heritable (h 2

0.2), whereas being a victim had a heritability
close to zero. A simpler way of recording (and analyzing) is to just record
the sum of attacks given by each sow and base the genetic evaluation on that
sum. This gives a higher heritability and would work well in practice. In a

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