He had heard through his travels about hanyo. Those who had blood of both human and youki. Most had problems with their baser instincts, unlike youki which were more animal than human and when they took to a human form they were still ruled by the beast.
Those mixed were unbalanced in the power of their parents so their beastial instincts could not merge with their human mind.
Sesshoumaru was getting ahead of himself thinking this way.
First he had to deal with the threats to that which he had claimed. Between the threat of Takemaru and the unrest in the northern territories he would have to tread carefully.