Is there a formula you can follow? A data base you can plug a pedigree into? I have an Appaloosa mare that is at least 1/2 TB, from what I can tell. Her sire is 1/4 TB, her dam is race bred and I THINK 3/4 TB, it gets confusing because the Apps in her pedigree are 1/2 TB or 1/2 QH, but the QH’s are 1/2 TB… Have I lost everyone yet?
It may not be AS confusing with WB’s but you must have similar problems when trying to figure out how much blood is in a pedigree.
The percent TB shows up on the Dutch site (http://www.horsetelex.nl), but a horse has to be in their database. There are non-Dutch horses in it.
If the pure TB show up as such in the pedigree, go back as many generations as you can and do the math, assuming that any horse that doesn’t show as TB is 0%. It will be off; how much so will depend on the inappropriateness of the assumption. So, using this as a sample: http://www.allbreedpedigree.com/aldebaran13 and using the great grandparents, the horse in question would be 5/8 TB (5 TB out of 8 total ancestors in that generation), or 62.5%. The same horse, as calculated by the Dutch site is 66.4% (http://www.horsetelex.nl/horses/pedigree/255464?levels=6), with the difference due to the fact that at least one of those three non-TB ancestors has some TB blood.
Thanks for the response, Peggy. I was hoping that there was an easy way to do it. 
After many math problems, I deduced that my mare’s sire is 5/16 TB and her dam is 11/16 TB making my mare ½ TB (even though if you looked at her pedigree you would think she’s mainly Appy with some QH thrown in!).
Now to decide if I want to breed her to a TB or a Trak… I’m leaning toward Trak… 
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