I just want to report, I was teaching the Mountain Horse his tricks, I got to the 2 one, which was help and after mastering it, the 'Feed' option has disappeared. He seems stuck at 12 like and 50% hunger.
So, It seems that if you feed them to Like 11 then the feeding options goes away, if you Use the naming method and raise their like, you can perhaps bypass this.
PS. This problem also seems to apply to the Raptor as well. It might be best to use the naming method to raise like and after unlocking the 'Help' trick, then feed them only as needed.