You need to borrow a hay corer. Do you have a feed store that tests hay? or a cow farmer, hay farmer or even an Agriculture Office that might have one? If you go to www.dairyone.com and read some of the information on that site, you'll get an education about hay. We recommend test # 603 at Equi-analytical (their sister site/same bldg). This will give you sugar/starch and the trace minerals that you'll need to balance. The test costs $49. Canada also has Al-Labs and the test we suggest there is F2-Forage pckg+NSC for $53.
You'll have to ask the company that makes the cubes you are feeding for an analysis. We aim for 10% or less sugar/starch a day. Soaking hay helps reduce sugar, you could probably soak/drain the cubes. How about Ontario Dehy Timothy Balance cubes? They are low nsc/mineral balanced! Be sure to grind your flax seed daily.
7#s of feed a day is good for a 350 pound pony this time of year. That 2% his body weight.
Mandy and Asher in VA