Date of this Version
The specific requirements for effective use of breed differences to meet specific production and market requirements are: (1) accurate assessment of production resources in regard to availability and costs, (2) accurate assessment of market requirements; Le., value differences in carcass composition associated with yield grade and quality grade, and (3) accurate current characterization of breeds in regard to such traits as: (a) growth rate and size, (b) carcass composition, (c) milk production, and (d) age at puberty. This information is needed to identify contributing breeds to use in alternative mating systems to achieve specific targets for production and carcass traits. The objective of the beef cattle industry is to synchronize production and carcass characteristics of breed resources with the production resources that are most economical to provide in order to maximize economic efficiency.
Information on breed differences is presented in another paper in this report, e.g., "Differences Among Parental Breeds in Germplasm Utilization Project."
The large differences that exist among breeds for most bioeconomic traits are the result of different selection goals in different breeds. Results from the Germplasm Evaluation Program at the U.S. Meat Animal Research Center provide evidence that genetic variation between breeds is of a similar magnitude to genetic variation within breeds for many bioeconomic traits. The heritability of breed differences approaches 100%, whereas, the heritability of differences within breeds for major bioeconomic traits varies from less than 10% to about 50%, depending on the trait. Heritability of breed differences approach 100% because estimates of breed differences are based on the means of a large number of individuals from a representative sample. This results in averaging genetic differences between individuals within breeds. Estimates of heritability of differences within breeds are generally based on single observations of individuals for a specific trait. Thus, selection among breeds is considerably more effective than selection within breeds.
Breed differences in bioeconomic traits are an important genetic resource and can be used to achieve and maintain performance levels that are optimum for different production and marketing situations. In addition to using breed differences to optimize production and carcass traits or to meet specific targets, the mating system should be organized to achieve and maintain high levels of heterosis or hybrid vigor.