Editor's note: In the October 2009 issue of Horse & Rider, Dr. Barb Crabbe explores how various metabolic disorders can increase your horse's risk of laminitis ("Founder Factors: Cushing's and Beyond").
Here, to help you better understand the relationships between Cushing's disease, insulin resistance, and founder risk, Dr. Crabbe introduces three different patients and tells you their stories. Meet Donovan, Maggy and Elmo.
Donovan is a 12-year-old Quarter Horse gelding. He's been out of work for several years because his owner just hasn't had the time. He's overweight, with fat deposits on the crest of his neck, in the depressions over his eyes, and over his hindquarters. He recently became sore in both front feet, with strong digital pulses--classic founder symptoms.
Diagnostic tests: Insulin, glucose, and ACTH testing was performed. His ACTH and glucose levels were normal, but his insulin was off the charts. Donovan has Equine Metabolic Syndrome--insulin resistance without Cushing's disease.
Treatment: His initial founder symptoms were treated with the nonsteroidal anti-inflammatory drug phenylbutazone (bute), and responded well. He was taken off pasture completely and fed a restricted diet of low-carbohydrate hay with no grain. As soon as his feet started feeling better, his owner put him back into a light exercise program of 30 to 60 minutes of daily walking and trotting under saddle; still, he remained obese, so he was started on thyroid supplementation. After six months, his weight was significantly down, his insulin levels had decreased dramatically, and he had no further founder symptoms.
He was slowly weaned off the thyroid supplementation and has continued to do well with nothing more than careful monitoring of his diet and a regular exercise program.
Maggy is a 20-year-old pony who's been obese most of her life, with fat deposits over her back and hindquarters. She's had several mild founder episodes in the past, and for the last two years her haircoat has been slow to shed. This spring she didn't shed at all, her haircoat began to curl, and she experienced a severe founder episode that didn't respond well to her initial treatment with bute and diet restrictions.
Diagnostic tests: Her insulin and glucose levels were both high, and her ACTH levels were above the normal range. Maggy has not only Cushing's disease, but also insulin resistance that's progressed to the point where her blood sugar level is no longer controlled.
Treatment: Maggy was started on pergolide, restricted from the pasture, and fed instead low-carbohydrate hay with no grain. She was given bute to help manage her founder symptoms. She couldn't be exercised, however, because her founder symptoms were too severe.
After 30 days on pergolide, her ACTH levels were measured again and although they were down, they were still too high and her dosage was increased. She has improved slowly since that time. Her haircoat has started to shed, and she's walking more comfortably. Even with careful management of her metabolic problems, her chronic founder will require long-term management. Her insulin levels remain high, although her glucose levels have returned to normal.
Elmo is a 25-year-old Thoroughbred gelding who was retired several years ago. He's been shedding slowly over the past few years, and last year his haircoat seemed to grow even longer and started to curl. He was having trouble chewing properly, and the vet discovered two rotten teeth that had to be pulled. His owner also thought he'd been acting "spacey" recently--he even collapsed several times.
Diagnostic tests: Elmo's insulin and glucose levels were normal, but his ACTH was slightly high. To confirm a diagnosis of Cushing's disease, the vet performed a low-dose dexamethasone suppression test, and the results supported that diagnosis. Elmo has Cushing's disease without insulin resistance.
Treatment: Elmo was started on pergolide. Not only did he shed his curly coat, but his behavior also improved and, at his next dental visit, his teeth and gums were in much better condition. Because he wasn't obese and didn't have signs of insulin resistance, no diet changes were necessary, and he has never had a founder episode.