Behavioral Genetics in Pigs and Relations to Welfare - Genetics and the Behavior of Domestic Animals - page 417

and the corresponding correlation with leanness was positive (r g 5 0.1 0.2,

2

more restless leaner). The genetic correlations between exit time and

growth rate was positive (r g 5 higher growth rate) and the

corresponding correlation with leanness was negative (r g 52

0.1, longer time

0.2, longer

time leaner). Selection for growth rate would thus lead to less excited ani-

mals whereas selection for leanness would lead to more excited animals.
D'Eath et al. (2009) recorded handling scores during weighing. Aggressive
behavior at mixing at 10 weeks was genetically associated with handling
scores at 22 weeks; pigs that fought and delivered non-reciprocal aggression
were more active during weighing whereas pigs that were bullied needed
more encouragement to enter the scale. When sow behavior was recorded
with a questionnaire in two populations, protests by the sow when moved to
the farrowing pen was heritable in one of them (h 2

0.2) but not in the other

5

( Vangen et al., 2005 ).

Lactating Sows' Aggression Toward Humans
Aggressive behavior of sows is more often observed when lactating sows are
kept outdoors or in family pens than indoors ( Wallenbeck et al., 2009 ).
Aggressiveness may be less of a problem for the caretaker if sows are kept
in stalls or crates. Even so, aggressive behavior of sows is not regarded as a
big problem in Sweden, where stalls for dry sows and farrowing crates have
been forbidden for many years. Less than 10% of the sows reacted aggres-
sively in a piglet-handling test where the breeder entered the farrowing pen,
lifted a 4-day-old piglet and squeezed it gently until it screamed ( Grandinson
et al., 2003 ). Avoidance of humans was also recorded in the piglet-handling
test and 70% of the sows neither moved forward nor withdrew from the
breeder. The heritabilities of aggression toward humans and avoidance were
estimated at 0.1 in that field study. Piglet mortality was not genetically
correlated to aggression but to avoidance (r g 5

higher
mortality). It must be noted that the genetic analyses included only 1100
observations and the standard deviations of these correlation estimates were
very large.
When aggression of lactating sows towards human was recorded with a
questionnaire to farmers, the heritability was estimated at 0.1 ( Vangen et al.,
2005 ). The heritability of fear of humans was estimated at 0.1

0.4, more avoidance

0.2 in the
same study. We do not know if these two traits are genetically correlated,
but admit that the thought of meeting a large sow who has no fear of humans
can be somewhat alarming, especially in outdoor production. In the study by
Baxter et al. (2011) , sows selected for higher piglet survival were both more
aggressive towards their piglets and towards the humans handling their pig-
lets. They were also more reactive animals, which suggests that farrowing
was a period of acute stress for these sows.