Perhaps an example of the methods sketched in the earlier post Piled Higher will help.

As a practical matter, having the genome is also going to make cattle breeding faster and cheaper.

Traits carried by bulls are important in determining how much milk a cow produces. Because bulls don't make milk, however, a bull's "performance profile" has to be sketched by observing the milk production of his daughters -- a process that takes about six years and costs $25,000 to $50,000. Now, male calves can be tested at birth for milk-enhancing traits using gene-chip technology.

Saving time and avoiding missteps are more important than the costs.