What strikes me as odd, is that you have no other hobbies other than the horse listed, with perhaps a touch of eating out.
Are you sure you don't do anything else? Or desire to? Own a cell phone?
Your pet (not horse) costs, other than the annual vet, don't seem to be listed -- how much do they eat? A dog, plus cat plus horse seems like a lot of pets for someone who just graduated. Bus passes?
As others have said, your housing costs are 1/3 your total take home, then the horse is pretty much 1/3, then you have only 1/3 for food, medical, dog, cat, car, bus pass, eating out, entertainment, savings, clothing, christmas, travel, laundry, friend's weddings that you are invited to, no horse shows, etc.
The only reason you are above water right now is that you are single, no kids, not dating (or there are no dating costs shown), and not saving much of anything.... and just graduated, so not used to having much other expenses, ... or perhaps others in your life used to help out the low income student (you) in small but regular ways, but you will need to step up now that you are making good money. Except that all of your money is tied up in horse + rent...
Some thoughts -- can you sell your car completely and give away your dog and cat, if they cost more than you listed and you want to keep the horse?
Can you find another way to reduce horse and rent costs (by working at the horse stable, or moving to a cheaper property with acreage for the horse and you take on the daily chores for the horse?)
What do your relatives and friends say to you about your financial / money choices right now?
How did you afford all of these animals last year?