I'm with justsambam. I know that it is stated in my boarding contract with my barn that if I am lacking payment exceeding X amount of days, then she has every legal right to take my horse as payment.
I don't think my BO would ever do that cause we are on a really good working relationship. I am sure that if I explained my situation, she would understand. But let's face it, it is a business and she needs money to care for the other horses. What happens if you are late on electrical bills, they turn off your electricity. Owning horses is not a necessity, it is a luxury and it takes time and money to give them proper care.
Sorry about your situation, but you need to think about this and talk with your BO. Good Luck!
All I pay my psychiatrist is the cost of board, and he'll listen to me any day.