Page 125 - Linear Models for the Prediction of Animal Breeding Values 3rd Edition

7 Maternal Trait Models: Animal

and Reduced Animal Models

7.1 Introduction

The phenotypic expression of some traits in the progeny, such as weaning weight
in beef cattle, is influenced by the ability of the dam to provide a suitable environ-
ment in the form of better nourishment. Thus the dam contributes to the perfor-
mance of the progeny in two ways: first, through her direct genetic effects passed
to the progeny and second, through her ability to provide a suitable environment,
for instance in producing milk. Traits such as birth and weaning weights in beef
cattle fall into this category and are termed maternally influenced traits. The abil-
ity of the dam to provide a suitable environment for the expression of such traits
in her progeny is partly genetic and partly environmental. Similar to the genetic
component of an individual, the maternal genetic component can be partitioned
into additive, dominance and epistatic effects (Willham, 1963). The environmen-
tal part may be partitioned into permanent and temporary environmental compo-
nents. It is the maternal additive genetic component of the dam that is passed on
to all her offspring, but it is expressed only when the female offspring have prog-
eny of their own.
In the usual mixed linear model for maternally influenced traits (Eqn 7.1) the
phenotype is partitioned into:

1. Additive genetic effects from the sire and the dam, usually termed the direct genetic
effect.
2. Additive genetic ability of the dam to provide a suitable environment, usually termed
the indirect or maternal genetic effect.
3. Permanent environmental effects, which include permanent environmental influ-
ences on the dam’s mothering ability and the maternal non-additive genetic effects
of the dam.
4. Other random environmental effects, termed residual effects.

In this chapter, the mixed model methodology for genetic evaluation in models
with maternal effects is discussed, considering a univariate situation, and the exten-
sion to multivariate analysis is also briefly presented. The application of BLUP to
models with maternal effects was first presented by Quaas and Pollak (1980).
When repeated measurements for maternally influenced traits are available
over a range of ages (for instance, body weight from birth to 630 days), a random
regression model (see Chapter 9) might be more appropriate to analyse such a
trait. A random regression model for maternally influenced traits is briefly defined
in Section 9.3.6.

© R.A. Mrode 2014. Linear Models for the Prediction of Animal Breeding Values, 109
3rd Edition (R.A. Mrode)