Global Endurance - http://globalendurance.typepad.com/global-endurance-blog/2010/04/considerations-for-selecting-an-endurance-horse.html
We want to share with you a couple of conformation observation in the lower leg of an endurance horse. This could make a difference in the soundness of an endurance horse in the long run.
As a general rule, the center of the canon bone should be supported by the heel of the horses hoof. If this is not the case, the load factor on the superficial and deep flexor tendon is greatly increased. Furthermore, the digital cushion inside the hoof is not supported anymore. Look at the different pictures below and see the difference in the alignment of the canon bone in relation to the heel of the hoof.
Let's call this horse A
The plum line from the center of the canon bone falls behind the buttress of the heel,
Now, let's compare the this with the two following horses, B and C