Obviously we are not concerned directly with the actual carcass attributes of the breeding cattle, but are concerned with the carcasses of the steer progeny. There is a strong correlation between ultrasound measurements of yearling breeding cattle and the actual carcass measurements of their steer progeny. This exact relationship is not absolutely defined, though. In many cases the actual steer carcasses will show even larger differences than the parental EPDs. Like any selection procedure, selecting cattle for one or two traits and ignoring everything else is a mistake.
Genetic correlations exist between many economically important traits.
Cattle that are extremely high in one trait are many times extremely low in another. Multiple-trait selection is the only sensible way to make selection decisions, particularly with carcass traits. There are Hereford cattle that are lacking in fat thickness, ribeye area or intramuscular fat genetics, like many individuals of any breed. Selecting for carcass traits may or may not be economically feasible in an individual situation. If a breeder needs improvement in one of the carcass traits, it may actually be more beneficial to cull some animals that are poor in that trait, rather than selecting those that are superior in that trait.