Methods for calculating economic weights of important traits in sheep

Abstract

Selection of animals is performed on the basis of a complex of traits, which are characterised by their breeding values and economic weights. The economic weight (EW) of a trait is defined as the change in economic outcome of a production system caused by a change in the genetic value of the trait. The methods used for the calculation of EW can be divided into two - objective and subjective. Using subjective methods, the EW of the traits are set by subjective decisions of the breeders or are calculated according to desired gains in the given traits. The objective methods describe the behaviour of a production system while increasing the genetic level of a trait. Production systems can be modelled by positive or by normative approach. The main disadvantage of the positive approach is the evaluation of historical data (level of the traits and prices achieved in the past) while breeding is oriented towards the future. Normative approaches describe relations between the levels of important traits and the economic result of the production system using profit functions or bio-economic models. These methods are preferred by many authors. The major advantages of profit function are the simplicity and facility for interpretation of results. Bio-economic models consist of a set of equations characterising biological and economic parameters of the system. The main advantages are precision, flexibility, inclusion of many biological details and a more accurate reflection of trait change on overall profitability. These models are difficult to develop but they are most frequently used for the calculation of EW.