Behavioral Genetics in Pigs and Relations to Welfare - Genetics and the Behavior of Domestic Animals - page 416

The heritability for fear of human has been estimated based on growing
pigs, gilts, and sows. The response of pigs to humans tends to be more
heritable when the trait is recorded on animals isolated from the group. The
heritability of voluntary approach to a human (time to first contact) was esti-
mated at 0.4 based on isolated gilts ( Hemsworth et al., 1990 ) but the herita-
bility was only 0.1 when based on gilts in groups ( Hellbr¨gge et al., 2007 )
and 0.0 when based on growing pigs of both sexes in groups ( Velie et al.,
2009 ). The comparison must be done with caution since the animals belong
to different populations and also differ in age.

Easy to Handle
In growing

finishing pigs, the assessment of “easy to handle” can be per-
formed in association with a routine procedure that takes more time if the
pigs are not co-operative. Variation between breeds exists in this trait.
Terlouw et al. (1997) showed that Large White pigs react more strongly to
human presence than Duroc pigs. Lepron (2006) compared three genotypes:
a Large White line, a line intensively selected for loin and ham muscle
development (Meat line), and a line with Meishan and Large White genes.
The Meat line pigs took longer time to exit the pen, run more frequently at
weighing and required more human interventions when moved out of the
pen, as compared to the other lines.
Moving pigs is a common task on any pig farm. Pigs are moved
between pens, to the scale at weighing, to the boar at mating and on/off
the trailer when transported. This work is time consuming and there might
be an optimal tameness of pigs. Very flighty animals run off in the wrong
direction, jump over barriers, and can create chaos. Very tame animals
move slowly because they want to come close and interact with the care-
taker instead of walking in front of him/her. Day et al. (2002) found that
pigs exposed to a pleasant-handling treatment took more time to move out
of a pen because of reduced fear of humans. Grandin (1989) also reported
that handling becomes difficult when pigs are overly tame. The Meat line
pigs in Lepron's study (2006) also exhibited behaviors indicative of fear,
stress, and excitation, such as bouts and U-turns. Thus, they seemed more
nervous than the other two lines. Large White pigs also showed some
distinctive reactions to handling. They vocalized more and their heart rate
increased more than that of the Meat line pigs. Pigs from the line
with Meishan genes appeared to be the least stressed when moved out of
their pen.
Recent studies have shown that the response to weighing is a
heritable trait in young pigs: the heritability for score for restlessness in the
scale was estimated at 0.2 ( Holl et al., 2010 ) and for time to exit the scale at
0.1

0.2 ( Jones et al., 2009 ). The genetic correlations between restlessness
and growth rate was negative (r g 52 0.4, more restless lower growth rate)