In this case a producer would purchase, or raise as separate lines, all breeding stock. This system has become more popular in recent years, especially as commercial companies have developed and marketed their own female lines. In this case, the producer would need only one boar line since all matings will be terminal, that is, none of the offspring will be saved for breeding purposes. A producer should never select gilts from the market herd in this system because without knowledge of the ancestry of the female line, he or she will have no idea how fast heterosis will be lost by mating the home-grown females to a particular boar line. Another caution, don't assume that just because a gilt or sow is all one color that she is more purebred than a multicolored animal.
Color can be a poor indicator of actual ancestry.
Since a white hair coat is generally dominant over other colors in swine, a white sow may be hiding the fact that she is half duroc, or hampshire etc. The heterosis of the market animals will suffer accordingly if she is mated to the wrong boar. In this case, the Duroc boar is used to produce market animals and A.I. is used to generate breeding females. The same female herd is used for both purposes. A.I systems not only eliminate the need to maintain several separate lines, but also allows the producer to incorporate proven, often exceptional genetics much more cheaply than with the outright purchase of expensive sires.