A horse is a thoroughbred (only one breed in his origins)
or a crossbred (more than one breed in his origins).
You can see the breed of a horse looking at his origins chart >
Here you can see 4 hanoverians horses, but only one is a thoroughbred, because he has 100% hanoverian breed.
If your horse is a crossbred, and you want to have a thoroughbred horse, you can breed him with a thoroughbred horse, and then breed the foal with the thoroughbred horse again, during several generations, and you get a thouroughbred foal at the end
It's the average of the parents breeds
For one breed :
Foal's % Breed = (Mother's % Breed + Father's % Breed) /2
If a breed has less than 1%,
it dissapears from the origins chart
the breedor is a program from