In the late summer to early fall there is a peak in laminitis cases.
Headlines are already starting to appear blaming fall laminitis on fructans in grass. Don’t believe it.
Fructans are often called sugar, but they’re not. Fructans are a storage form of carbohydrate in plants, similar to starch in grains or glycogen in muscles. Fructans are found primarily in grasses that are tolerant of cold winters.
Research using a type of fructan found in chickory roots (inulin) found that delivering a large dose of that fructan by stomach tube could cause laminitis in much the same way that overeating grain can. However, the fructans in grass have a different structure and molecular weight. It has never been proven that grass fructans can cause the same damage as chicory fructan.
Furthermore, laminitis caused by fructan is dose dependent. To ingest as much fructan as it takes to cause laminitis experimentally, the horse would have to eat a whole day’s worth of grass with a fructan level of just under 30%, which simply doesn’t happen in most parts of the world, or with common hay types, at any time of year.
In fact, many horses that develop late summer and fall laminitis aren’t even on pasture. So, what is going on?
Beginning in late summer there is a rise in the level of the hormone ACTH. This usually peaks in September then gradually declines. For most horses, it causes no problems. If the horse has early Cushing’s disease, a benign overgrowth of part of the pituitary gland, the rise is exaggerated and the high cortisol it causes can induce or worsen insulin resistance. This in turn can cause laminitis if the sugar and starch levels in the diet are more than the horse can easily tolerate.
Although studies are not consistent on this, some research has shown a rise in insulin that parallels the seasonal rise in ACTH. If the horse already has insulin resistance, this seasonal rise could push the horse over the edge into laminitis.
If your horse develops late summer or fall laminitis, get your vet involved and test for ACTH and insulin. If very high, especially if the diet is already low sugar and starch, the horse may benefit from the medication pergolide, at least for part of the year.
Otherwise, the treatment is meticulous hoof trim/balancing and a very low sugar and starch diet with no hay or feeds over 10% sugar and starch combined. Mineral balancing further helps with insulin action, control of inflammation and tissue healing.
Eleanor M Kellon, VMD