Modern confinement facilities have increased the stress on a cow's hooves, resulting in a greater incidence of foot health problems than was common when dairy animals routinely had access to pasture. The trait must be of economic importance. The differences we see from cow to cow in a trait must partially result from genetic differences between the cows.
Variation is the key to genetic progress.
The range of genetic differences between cows must be large enough to let us choose the best. Enough daughters should be scored to calculate sire proofs on a large enough number of sires to select the best for future use. We have several standards for describing a desirable foot - deep heel, moderately steep angle of the front of the hoof to the ground, absence of spread toes, and relatively short claw length. Each of these components of foot conformation is a trait in itself. Current sire evaluations are based on composites of these traits in some breeds and on the individual components themselves in other breeds.