Several new animations were added for the horses, so now they can be given treats or you can pet them. This will not happen for the 'old' horses (they are too many to be regenerated). Right now the feeding is purely visual, however in the near future this will change and in order to feed the horse treats you would have to have them.

You will notice that the size of the adult horses is going to be different.
This was done to add some more realism to what the horses look like. This means that the size of draft horses > regular horses > ponies > shetland pony > miniature horse.

There have been complaints that buying a magic horse is too random, so a quick change was added for now. On even days all the horses bought from the magic shop will be females, while on odd days they will be males. On the even game days the horses will be males, while on the odd days they will be females.
Note: The game day is on the top-right corner of your game screen.
Update: In order to make it easier for you, the magic shop will tell you on the page the gender of the horses it sells and the time until the gender changes.