In order to compare a breeding program for welfare in
outdoor conditions with a conventional breeding program,
genetic gain was estimated for 3 simulated breeding goal
scenarios:
- Scenario 1, conventional scheme with 7 traits: litter size at
castration at 5 days (LS), piglet mortality from castration
to weaning at 7 weeks (PM), mean piglet weight at
weaning (PW), weaning-to-mating interval (WMI), average
daily gain (ADG) from birth to 20 kg (ADGw), ADG
from 20 to 100 kg (ADGf) and lean content (LC). Hence,
the breeding goal H1 for scenario 1 is:
H1 = EVPM × APM + EVLS × ALS + EVPW × APW + EVWMI × AWMI
+ EVADGw × AADGw + EVADGf
× AADGf + EVLC × ALC
where A are true breeding values and EV are economic
values for each trait. There are wide ranges of economic
values depending on regions, markets and production
systems. In order to have realistic current economic
weights, the economic values for the scenario 1 were
chosen based on available economic values for conventional
production in the literature, relative to litter size
(Table 1). Leg condition was not included in this scenario.
- Scenario 2, breeding goal with welfare considerations: all
traits from scenario 1 and leg condition of sows after first
lactation (LEGw) were included. Furthermore, non-market
values (NV) were given to two traits due to welfare
considerations in addition to the current economic values
(piglet mortality and weaning-to-mating interval). Hence,
the breeding goal H2 for scenario 2 is:
H2 = H1 + NVPM × APM + NVWMI × AWMI + EVLEGw × ALEGw
Based on weights used by Kanis et al. (2005), the relative EV
value of 37.5 for leg condition was assumed. The authors
considered thisweight to be the decrease in production costs
per slaughter pig from one point increase of sow's leg score.
NV values for piglet mortality and weaning-to-mating
interval (traits that were also present in H1), were chosen to
be equal to the EV values, so that total weights for these traits
in scenario 2 were twice as high as in scenario 1.
- Scenario 3, breeding goal for welfare: all traits from
scenario 2 were included, but with NV on LEGw and with
higher NV on PM and WMI:
H3 = H2 + NVLEGw × ALEGw