Fixed effects and genetic parameters for the combined LambPlan evaluation of Australian sheep

The Australian sheep industry consistently improves performance through genetic evaluation provided by Sheep Genetics. Sheep Genetics is developing an enhanced evaluation system combining Terminal and Maternal breeds into a single LAMPLAN analysis. This improvement includes a review of fixed effects to ensure their suitability and an evaluation of alternative methods for their inclusion. This study outlines the steps taken to model fixed effects directly within the model, rather than through pre-adjustment, and to estimate genetic parameters. In the updated multitrait analysis, two main changes were incorporated in the fixed effect model, 1) birth type and rearing type were combined into a single effect to account for their interaction, and 2) the age of the dam was fitted as class effect (rather than a quadratic polynomial). Including the effects directly in the model resulted in an improvement in the fit compared to using the current pre-adjustment methods. These enhancements should lead to more accurate breeding values for industry, and this will be the subject of further studies.