Finally, we allow the direct genetic effect of the pig itself and its mother’s maternal genetic effect to have a covariance via the third term in the str() function, which provides the structure information for the effects: str(pig dam us(2).nrm(pig)). The term
‘us(2).nrm(pig)’ indicates that the two previously identified model factors (pig and dam) have a variance-covariance structure that is the direct product of two terms: an unstructured variance-covariance matrix with dimension 2 and the additive relationship matrix based on the pedigree information from pigs: