Even gegoogled:
In grashooi (grass hay) zit volgens dit artikel 2 % zetmeel (starch):

-"grass hay averages about 8 % ESC(dm) (from a limited database) and 2% starch"

Stuk artikel met bronvermelding waar het in staat:
Glycemic carbs in hay and feed.
Horses vary in their reaction to carbohydrates, and so there are no absolute numbers that can be considered safe for every laminitic or insulin resistant horse. Newly available tests for Ethanol Soluble Carbs are probably the most important. Hopefully someday research will be done to help us know. ESC include glucose, fructose, sucrose, lactose and FOS, fructo-oligosaccharides, which are the very short chain fructans. FOS is very rapidly fermented, and apt to be the worst kind of fructan associated with abdominal distress. FOS also causes a glycemic response (Bailey, 2007) ESC is a sub fraction of WSC. As per the Dairy One database grass hay averages about 8 % ESC(dm) (from a limited database) and 2% starch, for a total of average 10%dm glycemic carbohydrates. Less than 10%dm NSC (WSC + starch) for hay or feeds has proven over the years to be a good target for a horse in trouble. Any horse that has acute laminitis or very high insulin levels should certainly be at, or below these levels. My IR ponies were able to eat 8% sugar + starch hay free choice without gaining weight. Of course the same horse may do fine on higher sugar + starch hay if regularly exercised and kept at a fairly high level of fitness. This is only one of many factors in managing insulin resistant, laminitic animals, which includes exercise, prevention of mineral deficiency and appropriate hoof care, but I feel the most important one. Mine are not the only horses that have had major improvement in long-term laminitis by minimizing sugar and starch in the hay.

(Bron: http://www.safergrass.org/articles/testing.html)