This form of breeding should only be done with SUPERIOR breeding stock on both the half brother and half sisters' dams side. As well as the sires'. If you are breeding stock that is not up to par as far as genetics and conformation is concered, then I wouldn't even think about it. You could run into risks of deformed calves or other un-wanted problems.haviris said:How bad would breeding half brother to half sister be? And what do you all think about using a bull out of a heifer?