Breeding values for bulls are expressed in relation to a base. In The Netherlands and Flanders, three bases for breeding values are defined, Black & White, Red & White and Local. Breeding values can be converted from one basis to another base by adding or subtracting a certain value to a breeding value.

The conversion factors to convert breeding values from one base to another can be found in Basedifference. If you want to convert a sire to another basis, you can use Sire Search.

Calculating breeding values for % fat and % protein per base
The breeding values for the percentages of fat and protein are derived from the breeding values for kg milk, kg fat and kg protein on the desired base and in the desired lactation. To do this, the average productions of the cows of that base population are used. If, for example, a breeding value for % fat on Red & White base has to be calculated, than the breeding values for kg milk and kg fat also have to be entered into the formulae on the Red & White base.
The following two formulaes are used:

F%fat = ((Fkgf * 100) - (Fkgm * P%fat)) / (Fkgm + Pkgm)

F%protein = ((Fkgp * 100) - (Fkgm * P%protein)) / (Fkgm + Pkgm)

in which:
P = average production of the animals of that base for the indicated traits.
F = breeding value for the indicated traits

The factors Pkgm, P%fat and P%protein are indicated per lactation in the following table:

Black & White173044,303,41
Red & White167074,513,50