The possible role of glucose, insulin
Researchers have found that "glucose is important in maintaining lamellar integrity and was shown to be essential for the
viability of hoof explants in culture (in vitro)."3 Hoof culture without glucose or inhibition of glycolysis causes basement membrane zone separation when under tension. This
finding suggests that high-circulating corticosteroid concentrations or inhibition of insulin activity could result in such
an effect in vivo. It is possible that in an insulin-resistant state, glucose transporters are downgraded in the lamellar
tissues, so glucose entry into the epithelial cells may be impaired, as has been demonstrated in chronic laminitis.
Infusion of large amounts of insulin has been reported to induce laminitis, but the amounts infused lead to circulating insulin
concentrations well above physiological concentrations. Although diet influences the insulin concentration in the blood, the
relationship among diet, blood insulin concentrations and laminitis remains unclear.
Insulin sensitivity has also been found to be affected by diet. Large fluctuations in glucose and insulin after meals high
in sugar may supply inappropriate signals of energy availability to the glucose regulatory system, altering insulin sensitivity
of the tissues.
In Thoroughbred weanlings adapted to a sugar-and-starch diet, insulin sensitivity was lower compared with weanlings adapted
to a feed rich in fat and fiber. Mature Thoroughbred geldings with normal body condition scores (BCSs) tended to have decreased
insulin sensitivity when adapted to a sugar- and starch-based diet. There may be a progression of insulin resistance in laminitis-prone
ponies, from compensated insulin resistance to decompensated insulin resistance later in the course of the disease.
Specific breeds suggested to have an increased risk of developing insulin resistance include pony breeds, Morgans, domesticated
Spanish mustangs, European warmbloods and American saddlebreds. But there is insufficient epidemiological information to confirm
whether there is an increased susceptibility to laminitis in these breeds.
Diet modification to reduce the risk of developing laminitis due to insulin resistance in predisposed breeds may be indicated.
Replacing starch- and sugar-based diets with properly formulated fat- and fiber-based feeds will produce a low glycemic index
and an insulinemic response and avoid the insulin insensitivity that develops during chronic adaptation to sweet feed.