There's a surprising amount to know about hay. First, hay can contain different types of grasses (timothy, fescue, brome, orchard grass, oat grass...) and legumes (alfalfa, clover...). And, like human food, the nutritional content of hay is highly variable due to factors like soil composition, rainfall, sunlight and harvesting.
In Tonka's case the most important thing to know is that hay contains sugars -- sometimes a little and sometimes a lot. Some of these sugars (fructan especially) have been implicated in the dietary imbalance that leads to bacteria in the hind gut producing an endotoxin that attacks the laminea holding the coffin bone to the hoof wall. An oversimplification to be sure, but an explanation for why laminitic horses need careful nutritional management. If you're really interested check out www.safergrass.org.
So Tonka is going on the Atkins diet for horses. With the help of an acquaintance at Unifeed in Chilliwack I was able to secure 150 bales of low-carb hay yesterday. We expect the fellow to eat about half a bale a day, so this should last us through to the next hay harvest and then some. Unlike most horses Tonka will be allowed to free feed, so that he can eat as much or as little as his body dictates that it wants and we can try to bring his gut back into balance. Founder is not a problem with the feet -- it is a disease of the whole body that simply manifests itself in the hoof.