To study the relation between the general behavior of the sow
and her piglets, piglets’ behavioral data were averaged per nest.
That way the behavior of the mother sow can be directly linked to
the average behavior of her piglets. Those means were modeled
using linear mixed models with sow behavior, day of lactation, and
time as fixed effects, and with random effects for sow, day of
lactation, and replicate. The correlation because of clustering within
sows and longitudinal nature of the study has been modeled using
random effects. More specifically, sow-specific random intercepts
and time effects have been included in all models. Different models
were used for different outcome variables; each analysis studies
1 particular type of behavior.