This mod can be applied to any horse (anything the player rides) and makes the mount not hostile toward the player's pets, companions, summons, and non-hostile characters. Likewise, those attacking the mount will also be made non-hostile toward it.
In short... it makes the player mount smarter determining friend from foe and also gives inappropriate combat a chance to stop.
To get the feature, go to the Black Horse Courier in the Imperial City Market District and look at the book "Horse Whispering" on the desk.
To first activate the feature, get on and then off your mount.
There is also a feature that helps your horse keep from wandering off. It will start to go, get about 10 paces, then turn around and come back to where you left it. The spot you left it is marked with a bucket of "horse feed". In addition, you may activate the "Horse Sanity" quest, and the location of the bucket will show as the arrow on your compass and map.