Breeding objectives and the relative importance of traits in plant and animal breeding: a comparative review

Breeding objectives always involve consideration of multiple traits, even in situations where output of a single trait is dominant. We review literature dealing with formal definition of breeding objectives. Involvement of farmers in the process of setting up breeding objectives is also considered. In the optimal selection index, the relative importance of a trait is scaled by its economic value, derived as marginal profit related to a change in expression of defined size. Normative approaches to derive economic values use partial derivatives of a profit equation with respect to the traits involved or model the bio-economic system with various techniques. The theory is well developed and includes consideration of non-linear profit functions and traits with an intermediate optimum. It is frequently applied in animal breeding. In dairy cattle breeding, a major change of focus from traits related to output (i.e., milk yield) to traits related to cost of input (health, fertility, feed efficiency) has taken place recently. Plant breeders find the concept of deriving relative economic weights of traits difficult to apply and often replace the optimal index by restricted or desired gains indices. A change of paradigms similar to that in cattle breeding seems advisable. Participatory approaches to evaluate the relative importance of traits are more frequently applied in plant breeding than in animal breeding. We review two studies, dealing with methods of acquiring information about selection criteria of farmers planting maize in the Ethiopian highlands and of pastoralists keeping cattle in Uganda, in detail.