You have to ring them to find out - the Winter Farm ride whcih has quite a lot of jumps is open but the other bits depend on the weather and literally can be a day to day thing. They're open everyday though.
If you are lucky they might be open this weekend, if the dry weather keeps up. One thing is for sure its absolutely heaving on the first day they open, we went last year on the first day they were open for XC schooling and it was manic!