Since Update 35.3 the mechanics of horse breeding (and other animal mounts) are different from in the vanilla game.
There are three horse stats: health, speed, and jump height. Each of these are treated independently when breeding a new horse.
In vanilla, the horse stat of a new foal is a three-way average of the parents' stats and a third, random, unrelated value. This third value follows the same distribution as the stats of a naturally-spawned horse, but it cannot be influenced in any way. This means that all horse breeding tends towards the average over time, and thus it is almost impossible to breed two good horses and get even better ones.
In the mod, however, the horse stat of a foal is drawn randomly from the range of the two parents' stats - with a little variance either way. This means that breeding two good horses stands a good chance of producing even better ones. There may be a chance to produce worse horses, but they will not be significantly worse than the parents, and breeding does not tend towards the average naturally-spawned horse.
Health can vary by up to 3 above or below the parents' health range, and is capped between 12 - 48.
Speed can vary by up to 0.03 and is capped between 0.08 - 0.45.
Jump height can vary by up to 0.1 and is capped between 0.3 - 1.0.
These caps are in most cases a little wider than the possible range of naturally-spawned horses. This means that even 'perfect' horses can give rise to slightly better horses through selective breeding.
These changes apply to all other animal mounts. Different mounts have different stat ranges, both for naturally-spawned and in breeding. For example, a naturally-spawned Rhino's maximum possible health is greater than the maximum possible health of a naturally-spawned horse, and through breeding it may be increased even further. The health of a Giraffe, on the other hand, although its naturally-spawned range is the same as for horses, cannot be increased through breeding as much as a horse's health can. The possible breeding range for most mounts can be found in the succeeding table.
| Health | Speed (bps) | Jump (b) | |
|---|---|---|---|
| Horse | 12-48 | 3.44-19.35 | 0.700-5.920 |
| Wild Boar | 10-30 | 3.44-15.05 | 0.700-5.920 |
| Shire Pony | 10-28 | 3.44-12.90 | 0.354-5.920 |
| Rhino | 20-50 | 5.16-18.06 | 0.354-3.971 |
| Giraffe | 12-34 | 3.44-15.05 | 0.354-5.920 |
| Elk | 16-50 | 3.44-14.62 | 0.700-5.920 |
| Camel | 12-36 | 4.30-15.05 | 0.120-2.368 |