The text on this in in the development stage as I get my thoughts scattered through a 100 page spiral all cohesive and into a readable and understandable format. This may and probably will change.
When a horse is claimed as an import or bred as an offspring, it's stats also get rolled as a standard starting point. These points get handed to the owner for them to divvy out as they prefer according to the goals for the horse they are taking on. With this system it allows you to customize your horses as much as you like within the limits.
Import horses get 350 points by default. This base number gets a modifier roll and will raise the base stat points (never lower) anywhere from 0-10%. Offspring get the breeding calculation for stats with a modifier roll of anywhere from -5% to +5%. This calculation is figured as the sum of the stats/