While the previous model seems reasonable as a first approximation, it is common in livestock species to include maternal effects in the model. These effects are especially important for growth traits and recognize the importance of the maternal environment for the performance of an individual. Maternal effects from the progeny’s standpoint are environmental but have a genetic component in the mother; further, the genetic component of the maternal effect may have a covariance with the progeny genetic effect. This double structure can efficiently be accommodated in ASReml. Using the same data just seen, we can expand the previous model as follows:
Code example 4.5: Animal model for pig data, continued (Code04-‐5_AnimalModel.as)