Development of economic selection indices for beef cattle improvement

Profitability is the primary goal for most beef cattle producers. The main source of long-term profitability for a beef cattle operation lies in its production efficiency relative to other operations (Harris, 1970). There are numerous approaches to achieve greater efficiency including nutrition, reproduction, management, and genetics. The goal in animal breeding and genetics is to improve animal populations and future generations of animals (Dekkers et al., 2004). Expected progeny differences (EPD) are the traditional genetic tools used to select parents. A drawback to EPD is that they represent genetic merit in only one trait while in reality multiple traits influence an animal’s value (Hazel, 1943). With EPD as a sole selection tool, producers are left to individually determine their optimal use and ultimately the economic importance of each trait (Bourdon, 1998). Selection indices account for multiple traits simultaneously and consider both biological production levels and economics (Parish, 2011). Falconer and Mackay (1996) recommend the use of selection indices for multi-trait selection in animal populations. According to Hazel and Lush (1942), selection for an index which gives proper weight to each trait is more efficient than tandem selection or selection for multiple traits with independent culling levels. Tandem selection involves selection for one trait at a time until all traits have been improved to the desired level. This method is inefficient because selection pressure is placed on only one trait at a time, making genetic progress slow. Additionally, progress made in one trait could be eroded as selection pressure is placed on a different trait. When selection is based on independent culling levels, a certain level of merit is established for each trait and all individuals below that level are culled regardless of their performance in other traits. The main concern with this method is that an animal with superior performance in many traits may be culled if it is barely under the thresh hold level for just one trait. In this situation selection indices are an appropriate alternative because they allow for superior performance in one trait to compensate for poor performance in other traits