2. Materials and methods
2.1. Which traits need to be improved?
Outdoor pigs are kept in a more demanding environment
compared to indoor pigs (Edwards, 2005). For instance,
better maternal abilities are required when there is no
housing-protection of piglets in the field (Johnson et al.,
2008). Disease resistance is also an important issue in pig
production. Outdoor production causes some differences in
health problems compared to indoor production (greater
endo- and ectoparasitism pressures, lameness and arthritis;
Presto et al., 2007), especially when routine prophylactic
treatment with drugs is not permitted (such as the directive
for organic production in Sweden; KRAV, 2008). However, a
number of questions must be answered before including
disease resistance in a breeding program, such as defining an
appropriate measure of disease resistance and to identify
correlations between disease resistance and other traits.
Therefore, we did not select for disease resistance in this
study, but we focused on other traits related to health, such as
strong legs, good reproduction and low piglet mortality.
Selection on behaviour traits such as aggression, nibbling, ear
and vulva biting and some stereotypies could be important
when breeding for welfare. However, aggressive behaviour
and vulva and tail biting should be a minor problem if the
animals are kept outdoors on pasture (Wallenbeck, personal
communication). Furthermore, direct genetic selection on
animal behaviour may be in conflict with the dogma of animal
welfare that allows animals to express their “natural”
behaviour (FAWC, 1979). Hence, the present paper focuses where A are true breeding values and EV are economic
values for each trait