A typical ration for a 1000 lb horse might consist of free access to top quality hay, preferably a straight grass or grass/alfalfa mix or pasture, plus 2 to 8 lbs of a feed designed for old horses, plus free choice water and salt. Avoid straight alfalfa.
The monster is described as "Hideous" which closely relates to "Ugly." With previous knowledge we know that Frankenstein is a monster, and he isn't created to be beautiful or charming.