Hoof Nutrition Intelligence is a twice-a-month web segment that is designed to add to the education of footcare professionals when it comes to effectively feeding the hoof. The goal of this web-exclusive feature is to zero in on specific areas of hoof nutrition and avoid broad-based articles that simply look at the overall equine feeding situation.
Below you will find the latest question and answer installment that you can share with your footcare clients.
Q: Is my insulin-resistant horse likely to suffer from laminitis?
By Eleanor M. Kellon, VMD
A: The Equine Cushing’s and Insulin Resistance Group outreach forum has been in existence for almost 20 years and currently has over 11,000 international members. As you might expect, many members seek help from the organization when their horse, pony, mini-horse, donkey or mule becomes obviously laminitic. Others report issues confirmed by blood work, but state they have never had problems with laminitis.
Unfortunately, they’re wrong!
Back in 2004, Phil Johnson at the University of Missouri and colleagues published an article entitled Endocrinopathic Laminitis in the Horse. They described a “remodeling” of the laminae that occurs in horses with EMS or PPID (Cushing’s disease). Specifically, they found that lengthening and thinning of the dermal lamellae that leads to weakening and predisposes to separation, with resultant white line widening, rotation and sinking. This occurs without the basement membrane damage and white blood cell infiltration characteristic found with other types of laminitis.
Of particular interest was the fact that these changes are clearly visible microscopically, and on radiographs in horses not showing any obvious signs of pain, inflammation or lameness.
Johnson focused on a possible role for cortisol in these changes, but more recent research has clearly shown insulin elevation is to blame. While exactly how this happens is still unclear, there is growing evidence that insulin may be acting through the IGF-1 (insulin-like growth factor) receptors to cause increased cellular proliferation.
There is some discrepancy in published studies regarding whether or not dermal and epidermal tissues in the lamellae express insulin receptors. If they do, the high insulin levels may stimulate the changes seen via those receptors. In humans, epidermal keratinocytes stimulated with insulin show the same proliferation and elongation seen in the lamellae.
It’s also been shown that endocrinopathic laminitis, like human metabolic syndrome, is characterized by increased levels of the potent vasoconstrictor endothelin-1. This may be causing cellular proliferation via endothelin receptors with a reduction in perfusion and delivery of oxygen/glucose to the laminae.
Positive responses to herbal and amino acid support for nitric oxide generation suggest this is part of the mechanism. Hypoxia (low oxygen tension) also causes migration and proliferation of keratinocytes via release of HIF-1 (hypoxia inducible factor). The imbalance between vasodilating nitric oxide and vasoconstricting endothelin-1 is directly caused by high insulin levels within the blood vessels.
The important thing to realize is that these changes are taking place in every horse with elevated insulin, whether they are recognized to be in pain or not. Low-level lameness is easy to miss because the pain is symmetrical (no head bob). More subtle signs include less spontaneous activity, a reluctance to make sharp turns, muscle tension in the forearms, back and hindquarters, more rigid head carriage (high or low) and a subdued attitude. Horses with these concerns can easily be pushed over the edge into more severe pain by dietary indiscretions or even cold weather.
The good news is that meticulous attention to dietary simple carbohydrates, calories, weight, mineral balancing and additional nutritional support as needed is very successful in controlling insulin and restoring your horse’s love of life.
If you suspect a horse has a high insulin level, ask for a diagnosis and take correct action. Don’t allow hoof damage to progress to the point of being crippling.
Dr. Eleanor Kellon, a staff veterinary specialist for Uckele Health & Nutrition, has been an established authority in the field of equine nutrition for over 30 years. The owner of Equine Nutritional Solutions in Robesonia, Pa., she is a founding member and leader of the Equine Cushing’s and Insulin Resistance (ECIR) group, whose mission is to improve the welfare of horses with metabolic disorders via integration of research and real-life clinical experience. Prevention of laminitis is the group’s ultimate goal.
Click here to read more installments of Hoof Nutrition Intelligence.
Hoof Nutrition Intelligence is brought to you by W.F. Young Co. (Absorbine). 
Like many significant achievements, Absorbine® grew out of humble beginnings—and through the tenacity of someone willing to question the status quo. In this case, it was a young woman in late 19th-century Massachusetts: Mary Ida Young. Her husband, Wilbur Fenelon Young, was an enterprising piano deliveryman who relied on the couple’s team of horses to make deliveries throughout the Northeast. Inspired by Mary Ida and Wilbur’s vision, Absorbine® has continued to add innovative products throughout the years — products used every day by horse owners around the world. Which is why, since 1892, we’ve been The Horse World’s Most Trusted Name®.