Objectives in pig breeding

Abstract

SUMMARY 1. Some criticisms of the classical approach to constructing a selection index are advanced. This approach (the economic model ) is contrasted with an alternative one (the biological model ) which is derived from the concept of the biological efficiency of production of lean tissues. The selection objective which is proposed from the biological model is the improvement of lean tissue feed conversion. The most important single means of achieving this is increasing the lean tissue growth rate. 2. The approaches were compared in three studies: ( a ) the effects of errors in economic and genetic parameters of the economic index; ( b ) phenotypic relationships between biological objectives and other measures of performance; ( c ) a theoretical model based on the utilization of metabolizable energy. 3. In a fixed situation the results were similar for both models, but the main advantage of the biological model is that it gives good indications of what happens, and what selection policies should be, in different situations. In addition, lean tissue feed conversion and lean tissue growth rate are closely related to concepts widely applied in biology, and their use as selection objectives should be helpful in enabling workers in many disciplines to make use of each other's knowledge.