Let’s suppose that your main objective is to increase the genetic potential for milk production.
If this is the primary goal, and it probably should be, then you should select solely for milk production.
If you put emphasis only on milk production in a breeding program, then you will make maximum progress for this trait.
If, however, you select for two traits at the same time, you have lowered your progress in milk production (the primary trait) to 71 percent of the maximum.
Likewise, if you select for 10 traits, you have seriously reduced your potential increase in milk production to only 32 percent
of its maximum.
It is not difficult to include more than 10 traits in a selection program.
The economic traits most often selected for are the production traits of pounds of milk, fat or protein.
Many producers place additional emphasis on functional traits—feet,legs, udder support or teat placement, among others.
Some additional traits placed in selection programs are purely cosmetic in nature—rumps, heads, strength and
toplines, to name a few.
If a selection program contained all of these traits, the progress that would be made in the economic (production) traits would certainly be minimized.