A B C D from same bitch....A, B C same litter or same parents , D half brother/sister mate D to both A+B, best workers from those mated together, mate back D, best back to C or AB.. thats if they all work by which point ABC+ D are now to old to breed, plus the parents of ABCD could well have been bred the same way so good and bad points are just waiting to jump out ....you also need to mate ABCD to new blood and test it and bring it in at a later date at maybe 33% 25%, i like it to be 12%...
so the turth is half the time if your testing your dogs and then breeding them your line/inbreeding pl