You still have to do it yourself, you can just select the horses with one click 

I had this too - if you go to Horses - Manage there should be an option to feed/water/groom all :) You'll still need to do it manually but it's one click like Wireless Mouse said instead of doing each one! 

oh, for me all i have too do is go to their file and check >eat from feed storage and > drink from water storage and then when their hungry or thirsty they can eat or drink. (you just have to make sure you have feed and water in storage)

@ Ruth, that's a completely unrelated mechanic to the question. You do not need to buy the employees at all to do that.

The employees are preferable over feed/water from storage as you constantly have to buy more feed & water anyway to keep the storage full, and storage for the feed and water takes up some of your acreage, which can be put to better use with horse stalls or show arenas. Additionally, you can only do this with horses boarded with you. 

Thank you guys! I knew it was simple I just couldn't remember lol