Expected Progeny Differences (EPDs) have been around for decades and are the best tools available to use in selecting sires with desirable genetic potential as parents.
A recent webinar titled "Genetic Selection Tools in Beef Cattle: EPDs and Antagonisms" outlines how to understand and utilize EPDs in selection.
When selecting sires it is critical to understand potential genetic antagonisms that exist to ensure marketing goals can be met while fitting within environmental constraints. Selecting for increased milk and early growth can be detrimental in some environments and in cases where replacement females are retained and maintenance costs are a concern. Additionally, selection for decreased calving difficulty could potentially lead to replacement heifers that have slightly more difficulty giving birth during their first parity
There are scores of EPDs available and selecting to improve multiple traits simultaneously can be cumbersome – just open up any sale catalog and it is easy to become confused immediately. Economic indexes can help alleviate this confusion. They do so by combining multiple Expected Progeny Differences (EPDs), each weighted by an economic value, into one numeric value often expressed in dollars per animal.
Economic Indexes Defined
An economic index is a collection of EPDs weighted by their economic value such that traits with greater impacts on production goals have a larger economic weight associated with them. The basic equation of an economic index is:
I = EPD1 x a1 + EPD2 x a2 + EPD3 x a3…EPDn x an
Where: I is the index value; EPDn is the EPD for trait n; and an is the economic weight associated with trait n.
Angus, Hereford, Charolais, Gelbvieh, Limousin, Red Angus, and Simmental all publish at least one economic index.
A recent webinar titled "Genetic Selection Tools in Beef Cattle: Economic Indexes" explains how economic indexes are calculated and provides information on a number of the breed indexes available.
A full description of all available economic indexes can be found in the University of Nebraska NebGuide G1847 Economic Indexes for Beef Sire Selection (PDF version, 374KB) and a full description of all available EPDs can be found in the University of Nebraska NebGuide G1967 EPD Basics and Definitions (PDF version, 704KB).
Matt Spangler, Ph.D.
Associate Professor and Beef Genetics Extension Specialist
University of Nebraska–Lincoln