The P value of the interaction between birth weight and age (BWT×age) tests whether the difference
between NBW and LBW piglets is the same across all age groups. If the P value of BWT×age > 0.05,
the difference between NBW and LBW piglets is the same across all age groups. If the P value of
BWT×age < 0.05, the difference between NBW and LBW is different at various ages. In this latter
case, the two subsequent P values of birth weight and age are irrelevant and have been excluded
from the table.