For each stat title, there is a natural stat, an actual and a potential.
The natural stat is the descriptor found below the numbers. In this case, Strength is Extraordinary, Intelligence is Extremely Good, etc.. Speed is the best natural stat on this horse at Inconceivable. Natural stat titles are determined at birth based on the parents' natural stat titles and the breed of the horse. These will get better with training. The descriptors, in order from worst to best are:
Poor
Below Average
Average
Fair
Fairly Good
Good
Very Good
Extremely Good
Superb
Fantastic
Extraordinary
Amazing
Phenomenal
Inconceivable
The actual stat is the number in parenthesis. Strength is 208.23, Intelligence is 203.22, etc. Actual stat titles are most used in events. The higher the actual in a determining stat, the better the odds of winning. Events often don't take certain stats into account, while others are judged on all stats.
The potential stat or percentages are the first number there. Strength is 202%, Intelligence is 235%, etc.. Potential is what ties the natural and actual stats together. All horses are born at 90 or 95% (for sponsors with breeding skill) of their potential.
How the stats are related to each other
At birth, a foal is born at 90 or 95% (sponsor breeding skill) of its potential. The natural stat is based on both parents' natural stats and the breed of the foal. For instance, no matter what the parents' natural stats are, a Quarter Horse foal will never have Inconceivable endurance.
Within the natural stat (Good, Amazing, etc.) is a range of actual stats a foal will be given. For example, you will never see a .01 horse with an 'Inconceivable' natural endurance with an actual stat of 65. The foal is more likely to have an actual stat in the 110 or better range if it has an Inconceivable natural stat.
As you start training the horse, the actual and potential stats raise together at about the same rate, though the potential is a little slower than the actual. When a horse reaches 450 points in actual stats, the highest and the lowest actual stat will start dropping percentages. In the case of the stats above, Endurance is the highest actual stat (209) and Speed is the lowest (202.89). These two stats will start lowering the potential (percentages) just slightly each turn the horse is trained in some way. The highest stat will drop about .03 per turn and the lowest stat will drop about .05 per turn. You can change which actual stats are high and low through training and diet.
Once a percentage gets low enough, the natural stat of the horse will improve. This is sometimes called rolling by players. The point at which the natural stat will "roll" depends on where the actual stat is at that point in time. The higher the actual stat, higher the potential can be for the natural stat to improve. At around 200 in the actual stat, the changes happen at about the following percentages:
Fair -> Fairly Good - 310%
Fairly Good -> Good - 285%
Good -> Very Good - 250%
Very Good -> Extremely Good - 235%
Extremely Good -> Supurb - 222%
Supurb -> Fantastic - 210%
Fantastic -> Extraordinary - 200%
Extraordinary -> Amazing - 186%/185%
Amazing -> Phenomenal - 174%
Phenomenal -> Inconceivable - 164%
The two other stats that can affect competition and are passed on to foals is Surefoot and Movement. Surefoot shows as a percentage and can reach 225 with shoes on. Movement is denoted by a description such as Normal or Superfluous and can reach 215 on the training page with shoes.
From worst to best the movement descriptions are:
heavy footed
normal
fairly light stepper
light stepper
extravagant mover
lavish Dancer
flamboyant
superfluous
fabulously gaited
To learn how to train your horse, you can visit the Player Provided Training Guides Section of the forums.
What should you event your horse in?
Eventing your horse
