How much does it cost to keep a 4 year old horse?

Depends on how you keep it and where you are. If you are boarding it, that can cost anywhere from $100-500 a month. If it's unbroke and you are a beginner you will have to pay to get it trained which could cost anwhere from $50-200 a month depending on the trainer. If it is broke then you wont have to worry about training. If you decide to keep it at home you will have to pay for hay in the winter which can cost up to $200 for the winter. And grain will be about $50 a month, all year long. Then theres vaccinations which are given twice a year and cost about 70 dollars the first time and 30 the second. Then theres dewormer which is 5-10 every two months. Then theres ferrier every two months which can cost from 20-40.

Personally, I board my horse at a friends house. She gives me free board, but I pay for all his needs. I pay about $100 a month on him, but hes a pretty cheap horse. So you could easily spend upwards of $2000 per year and more if you board.