Laminitis Lowdown by: Christy West, Digital Editor/Producer August 01 2010, Article # 16761 Add to Favorites ShareThis The laminitis mystery is far from solved, but researchers continue to discover new clues about its causes, treatment, and prevention. Laminitis, an often devastating hoof disease that can strike horses of any breed without warning, is a major issue for horse owners and veterinarians alike. In the recent American Horse Publications (AHP) Equine Industry Survey, nearly 50% of the 11,000-plus owners surveyed listed it as a health issue of concern. And in last year's AAEP (American Association of Equine Practitioners) Equine Research study, 63% of the responding veterinarians listed it as a health condition in need of more research, making it the No. 1 health problem listed on the survey. Some of the best minds in equine veterinary medicine have targeted this disease, and the pieces are starting to fall into place. Here we'll visit studies described by James Orsini, DVM, Dipl. ACVS, Penn Vet Laminitis Institute director; and Amy Rucker, DVM, of Midwest Equine in Columbia, Mo., who both presented at the Fifth International Equine Conference on Laminitis and Diseases of the Foot (Nov. 6-8, 2009). Laminitis Basics Laminitis is an inflammation of the laminae--interlocking leaflike tissues attaching the hoof to the coffin bone. It can strike any number of feet on any horse due to a variety of triggers, from high-carbohydrate diets in sensitive horses to colic to retained placenta to mechanical overload. Severity ranges from mild and curable to severe and incurable (resulting in euthanasia). Enzymes and the Laminitis Process A major focus in laminitis research has been enzymes (which catalyze or stimulate chemical reactions in the body) that get out of balance in early stages of the disease. It's been theorized that if these enzymes could be controlled medically, laminitis could be prevented or minimized. Previous work has often focused on enzymes called matrix metalloproteinases (MMPs), which have a role in hoof growth but become overactive in laminitis. However, more recent work has found that another enzyme, an aggrecanase termed ADAMTS-4, spikes much earlier in the laminitic disease process than MMPs (first reported by Orsini and colleagues at Penn in 2005). Christopher Pollitt, BVSc, PhD, director of the Australian Equine Laminitis Research Unit and research director of the Penn Vet Laminitis Institute, wrote that these findings "are causing us to rethink the early events that culminate in clinical signs of laminitis." Another researcher, Samuel Black, PhD, professor of Veterinary and Animal Sciences at the University of Massachusetts, discussed similar ADAMTS-4 findings, lending support to this line of research. Black also reported that certain molecules that help joint cartilage resist compressive forces (the proteoglycans: aggrecan and versican) have recently been found in the laminae, suggesting a similar role there. Thus, increased activity of the ADAMTS-4 enzyme that breaks down these molecules "may contribute to the loss of lamellar function in laminitis," he noted. Hormones and Laminitis Overweight horses are at higher risk for laminitis, often due to insulin resistance (a reduction in sensitivity to insulin that -decreases the ability of glucose to be transported into the body's cells from the bloodstream). Nicholas Frank, DVM, PhD, Dipl. ACVIM, associate professor of Large Animal Medicine at the University of Tennessee, noted insulin resistance can "lower the threshold" for laminitis in affected horses. He also noted small management changes, such as introducing a new batch of hay or feed with higher levels of nonstructural carbohydrates (NSC), stress increases, or exercise reduction, can push these horses over the edge. Frank reported that even healthy horses hospitalized for two weeks had increased insulin resistance, suggesting that stress and possibly exercise reduction can contribute to insulin resistance. "We haven't had any studies to support this in the past," noted Orsini. Nutrition and Pasture Management Horses with high body condition scores (7-9, fleshy to extremely fat; see www.TheHorse.com/pdf/nutrition/bcs.pdf for more on body condition scores), hyperinsulinemia (high levels of insulin in the bloodstream of 32mU/L or more), and cresty necks "are the ones you should look at very carefully, as these are good predictive criteria for laminitis development under certain conditions,"