See [http://wurmonline.com/forum/index.php?topic=55489.msg503824#msg503824 Rolfs forum post] for details.
====Important to note====
Players have observed that dead parents don't count towards the 'inbreeding' check:
"I have often used it as a method of breeding, to kill the old parents when I had too many horses that had a parent in common. After the parents are dead, you can breed and get normal horses. Leave the parents alive and you get lots of bad traited animals." [http://forum.wurmonline.com/index.php?/topic/62468-animal-congestion-fix/page__st__100#entry643716 Source]
== Caring ==