How breeding female days are calculated for each particular
system will affect the LSY calculation.
Systems where gilts are
already bred before they are entered into the sow herd do not
have additional acclimation days added into the LSY calculation.
The calculation also depends on the productive period
used for the calculation. For this study, the productive life for
a sow was the first successful mating date to the date when
the last litter was weaned.
When LSY is extracted from a herd
management software program, the productive period is not
uniform for sows that are still active in the herd.
For sows removed
from the herd, the period from culling to removal is included
and is presumably not the same for each sow.
The
additional NPD from culling to removal would reduce the LSY.