The retrospective index approach (Kanis et al., 2005) was
used to derive weights of traits related to welfare (PM,
WMI and LEGw). Total weights of these traits in scenario 3
were determined in order to make their genetic changes
positive. First, the effect of increasing one by one the
weight of sow's leg condition, piglet mortality and
weaning-to-mating interval, on the genetic response in
the breeding goal was performed to obtain the minimum
weight for the achievement of a gain in the trait. Secondly,
several combinations of weights on these three traits were
used to choose the breeding goal values corresponding to
improvement in all considered welfare traits.
In order to describe improvements in welfare traits relative
to themarket genetic gain, themarket genetic gainwas defined
as the genetic gain with breeding goal traits and economic
values from the scenario 1. Gains in leg condition, in piglet
mortality and weaning-to-mating interval were assumed to
have both market and non-market values. Non-market and
market genetic responses for traits (ΔGEV and ΔGNV, expressed
in trait unit) were estimated from the following formula:
ΔGEV = EV × ΔG
EV + NV and ΔGNV = NEV × ΔG
EV + NV .