Breann had a 25 year old black Missouri Fox Trotter gelding named Midnight. Midnight had been a personal trail and pack horse for Breann’s grandfather who worked for the Forest Service for 20 years until granddad gave him to Breann. She rode Midnight in parades and in 4-H shows, and she wanted to ride him as she vied for royalty of the local rodeo the following summer. But Midnight began to limp.

Breann’s mom, Jeanene, called us. I traveled with my husband and partner, Dr. Jim Latham, to the house. Midnight was an obese rascal, weighing 1272 pounds with a body condition score, BCS, of 8+. His coat was long, as expected for winter in Colorado, and he showed an enlarged sheath and bulging fat pads above the eyes. His hooves were flared and he was very lame in both front feet, sore at the apex of the frog to hoof testers. He had a history of a surgery on his left hind annular ligament many years before and he’d always rested his fetlock. We were suspicious that Midnight, with no known inciting stress or illness, but with his obesity, had developed laminitis, commonly known as founder.

Laminitis can be a devastatingly painful disease. The underlying pathophysiological events that lead to laminitis are still under intense investigation but it appears that inflammation in the hoof is common to most forms. The cause of the inflammation varies, but the result is swelling between the hoof wall and the sensitive tissues. The third phalanx, the coffin bone, may rotate from lack of support. Because of his age and clinical signs, we were concerned that Midnight might also have a hormonal disease, Pituitary Pars Intermedia Dysfunction (PPID), commonly called Equine Cushing’s Disease, which could also cause laminitis. PPID is one of the most common diseases in older horses. (See articles on Laminitis and Equine Cushings Disease –PPID- on this website)

We discussed laminitis and PPID and advised x-rays, lab work, and hoof care. Jim suggested restricting Midnight to 12-15 pounds of hay per day instead of the free choice alfalfa he was getting from a 650 pound bale set out in the middle of his paddock. He prescribed Bute for the inflammation and discomfort in Midnight’s hooves. The Weidmans considered their options for Midnight as a family.

A few days latter, we shot lateral x-rays of Midnight’s hooves and pulled blood for an Equine Profile and an endogenous adrenocorticotropic (ACTH) hormone test.

Blood testing for PPID is complicated. An overnight dexamethasone suppression test can be done to see if the steroid drug, dexamethasone, can shut down the production of cortisol from the adrenal gland, as it does in a normal animal. However, some clinicians are concerned that dexamethasone, a steroid, could make laminitis worsen in isolated cases. Alternatively, the endogenous ACTH test can be run, but it must be processed promptly and stored and frozen in a plastic tube before transport to a qualified laboratory. ACTH is also naturally elevated in the fall and early winter each year, so interpretation requires that consideration as well. A more complicated test using dexamethasone suppression and stimulation of thyrotropin releasing hormone has been researched. These tests all require significant planning and effort on the part of the veterinarian. Additionally, blood sugar and insulin may both be elevated, and the white blood cell distribution is occasionally affected by the disease.

Midnight’s x-rays showed rotation of the coffin bones of both front feet and high and low ringbone--periarticular and articular bone spurs (exostoses) at the proximal (pastern) and distal (coffin) interphalangeal joints. The front of his hooves had grown long until his hooves extended one inch beyond the ideal breakover point.

The lab tests came back with an endogenous ACTH of 203 (normal is 4.7-32.7). Even in winter, the interpretation had to be PPID, Equine Cushing’s Disease.

This particular malady develops when part of the hormone master gland of the body, the pituitary gland, located at the base of the brain, develops a hypertrophy that is no longer under the inhibitory control of the hypothalamus, another master gland located close by the pituitary. The overgrowing cells in the pituitary gland produce too much ACTH hormone which directs the adrenal gland to produce too much cortisol. In turn, the cortisol changes the metabolism of the horse. In addition, other hormones (pro-opiomelanocortin peptides, POMC, and melanocyte stimulating hormone) from the pituitary gland are increased that cause the growth of a heavy coat and sometimes increased sweating on the neck and shoulders. Midnight had some of the classic signs of PPID; increased water drinking and urinating, hirsutism (a longer, curly hair coat) a pot bellied look, cresty neck, fatty tailhead, a swollen sheath area, and fatty swellings above the eyes—the supraorbital fat pads--and laminitis.

More than 50% of PPID horses develop chronic laminitis. In PPID horses, the increased cortisol production from the adrenal gland causes insulin resistance or these older horses may also have preexisting abnormal glucose metabolism. As a result of insulin resistance, tissues cannot absorb glucose, and become starved of energy —which in the hoof can cause a separation of the laminae--laminitis. Whether there is also a direct hormonal vascular effect or toxin release from chronic infection that causes laminar inflammation is in question.

Untreated, horses with PPID have gradually reducing quality of life and are usually euthanized within a year. But there are treatments available that can maintain some of these horses for years.

Jim prescribed Permax (pergolide)-1 mg orally from a local pharmacy-to begin treating the Cushing’s and continued the Bute. Pergolide suppresses the ACTH secreting cells of the pituitary gland. The estimated yearly cost of Pergolide (approximately $500) seemed reasonable considering the improved health and pain free ambulation of this loyal old horse.

Jim discussed the x-rays with farrier Greg Wells. Greg trimmed Midnight’s hooves to ease his break over and tried Natural Balance shoes with rails—the EDS System of Gene Ovnicek. Jim and Greg kept in touch and as Midnight’s comfort increased, the rails were decreased.

Jim continued Midnight’s strict diet.

Photo courtesy of Jeff Layton, Pagosa Photography
Within one month, Midnight had lost 50 pounds and was walking much better. We suggested hand walking twice daily as he became more comfortable.

By spring, Midnight began to play in his paddock but he reinjured his left hind fetlock jumping over a mud hole and he required rest, wraps, and pain relief for a week. But his weight was down to 1142#, a loss of 78 pounds. We continued his pergolide.

In June, Midnight still had not completely shed his long, black winter coat and he had an infected canine tooth, still signs of Equine Cushing’s Disease. He remained slightly lame on his left hind leg. We rechecked the endogenous ACTH and discovered that it had only reduced to 152pg/ml, still well above normal. Midnight’s pergolide was doubled to 2 mg per day. Jim advised Jeanene that Midnight should be permanently retired, that he wouldn’t be able to carry Brianna as she competed for princess of the rodeo.

But Midnight trimmed down to a svelte 1080# and he happily moseyed about his short grass pasture with a buddy. Breann would ride him around the yard as he sampled the greener lawn with a comfortable stride and a glossy black coat. By winter, Midnight was feeling great. He opened his stall door and loaded himself in the open horse trailer. He was ready to go for a ride.
See Article:   |   Equine Cushings Disease  |  

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