High Starch Perennial Zone 5 Plants for Horses?

I'd like to find an invasive starchy plant for horse grazing. Grass is too high in sugar and clover and other legumes are too high in protein, both of which can cause major problems for horses who don't work much, which mine don't.

Anybody know of anything that'd fit the bill? Even a bush or tree that could be coppiced and thrown in would be alright but I was only able to find high protein tree leaves.

typically fractions of the product in leaves and stems..

100g provides as percentage of recommended daily allowance

18% Iron
17% Potassium
& Calcium, magnesium, selenium, copper and traces of other minerals.
4% Protein
6% Vitamin C
13% Thiamine
6% Niacin
& small amounts of other B vitamins

Contains: niacin, phosphorus, copper, magnesium, folic acid and pantothenic acid.

Properties: disinfectant, energizing and galactogenic. Jerusalem artichoke contains inulin, a carbohydrate close to starch, that can cause gas in some people. Delicate individuals or those eating Jerusalem artichoke for the first time should only eat a small portion.

Jeez George, you're quick on the draw. Thanks.

I changed the subject of the post from an info request about sunchokes because I just tried searching with different keywords and found a source saying sunchoke leaves were 28% protein. http://www.farmradio.org/english/radio-scripts/48-5script_en.asp. Odd that your source has such a different take on this...