Genetic Evaluation

Predictions of genetic merit for breeding animals is one of the oldest technologies available to mankind. Identifying animals for selection and mating has evolved from visual appraisal to sophisticated analytical models to predict additive genetic merit of animals. In North America, the standard for identifying genetic merit of breeding animals is expected progeny differences (EPDs). With very few ad hoc exceptions, EPDs are produced for North American beef cattle using models based on Best Linear Unbiased Prediction.

While not all economically relevant traits in all situations and in all North American breed registries have EPDs available, the number of traits and trait components that have EPDs has increased dramatically. Nearly all the major North American beef cattle breed organizations have migrated to weekly updates to their EPDs, eliminating the need for interim EPDs.

Most of the improvements in the technologies used to produce EPDs has been motivated by an opportunity to increase accuracy of prediction and reduce bias. For example, the advent of genomic information to enhance the accuracy of prediction has resulted in EPDs for most traits being produced using either Single-step Genomic BLUP or Single-step Hybrid Marker Effects Models.

In commercial cattle production, EPDs for economically relevant traits should be combined with appropriate selection tools such as selection indices to make optimal genetic progress. It must be remembered that EPDs are just parameters to make genetic progress and manage certain genetic risks.

In some special situations in seed stock production breeders may need to make selection decisions using EPDs that are not economically relevant traits in commercial settings in order to enhance the marketability of their breed or breeding animals. For example, if a breed has a perceived defect that is limiting that breed organizations' members from expanding their market for selling germplasm, then selection to improve that characteristic should be included in the seed stock breeder's breeding objectives.

Critical to the production of EPDs is having high-quality estimates of variance components. Knowing the heritabilities and correlations of the traits and performing multiple trait analysis enhances the accuracy of prediction and reduces bias from effects such as incomplete reporting.

[Not sure where connectivity goes] Connectivity (Suggested writer: Ron Lewis) Measures of (Suggested writer: Ron Lewis) Impact on GE (Suggested Writer: Ron Lewis)