Success Story: Treating Cushing's Disease
Republished with permission from UC Davis
Cushing's disease is an endocrine disorder of humans, dogs and horses. Equine Cushing's disease is caused by hyperactivity of the pituitary gland. The pituitary gland produces and secretes multiple hormones.
In horses, the brain may produce less dopamine (a neurotransmitter that acts as a control mechanism for a part of the pituitary gland). When the pituitary gland grows out of control, it secretes excessive hormones (MSH, beta-endorphin and ACTH) that appear to dramatically affect the immune system.
Though Cushing's disease is most common in older horses, especially ponies, all breeds and all ages can be affected. Cushing's horses are more susceptible to numerous infections including sole abscesses, tooth root abscesses and pneumonia. By administering a drug, pergolide mesylate, which behaves like dopamine in the horse's system, veterinarians can regain control of pituitary function and, potentially, restore the immune system's function back to what appears to be the normal state.
The following two stories of Cushing's horses treated with pergolide mesylate demonstrate the successful outcome possible with this treatment.
Jon Collins
Jon Collins before treatment. Though not an obvious case of Cushing's disease, his coat was dried and patchy and he showed signs of muscle wasting. His immune system was compromised as he suffered from a chronic skin infection.
After only two weeks of treatment, he substantially improved.
(Second from left) Jon Collins after treatment, shown with the Dixon Future Farmers of America Chapter. His coat's luster returned along with his energy and muscle tone.
Jon Collins was a kind and gentle Morgan gelding who, since the early 1960s, had been a member of Dixon resident Rhonda Rayn's family. Her grandparents owned his dam who had Cushing's disease. Mrs. Rayn used Jon Collins in 4-H competitions when she was a child and was delighted when her children were also able to use him for 4-H.
"He was a very sweet and loving horse," remembered Mrs. Rayn. "We did everything with him; he pulled a buggy, we showed him in 4-H. We had a lot of fun with him."
Back in 1995, Jon Collins was 33 years old and appeared to be at the end of his life. He was very thin and depressed, he had a widespread bacterial skin infection and was having difficulty rising. It was a hard decision but Mrs. Rayn decided to have the UC Davis Equine Field Service out to euthanize her horse. She said, "He looked pathetic. He was so thin, his hair was all brittle and burnt looking, he was losing all the hair on his hips and shoulders and every time he would lie down, the bare skin would crack and bleed. I didn't want him to suffer due to the infirmities of old age."
During their examination of Jon Collins, the veterinarians were intrigued by his "will to live" as he took them "lawn skiing" to get to the hay bales. Attending veterinarian Dr. Brett Sponseller suspected and diagnosed Cushing's. "The vets basically pleaded with me not to put him down," Mrs. Rayn said. "They told me to try him on the pergolide and promised me I would see results in two weeks."
Mrs. Rayn was understandably skeptical. "Yeah right, this little pill is going to transform my geriatric horse in two weeks! But it was amazing. I was shocked. You can't even imagine how he changed. He went from a horse that we were ready to put down, to a happy, energetic horse with a glossier coat who was running off the other horses from the feed tub. The hair filled in the bare spots and even his muscle tone came back and filled in where he had wasted away over the years. His skin infection cleared up and his appetite was back full force. Our kids were able to use him again for 4-H."
For three more years, Jon Collins was treated daily for Cushing's. Though his owner was very skeptical at first, she said she was extremely pleased with the outcome. She said the only downside to the pergolide treatment was the cost. It costs about $100 a month for the medication, but she said it was well worth the money. It was also easy to administer. Jon Collins ate his pill in an apple every day. Fortunately for horse owners, there is now a lower cost version of pergolide that has been specially formulated for horses. This should make treatment a more readily accessible option.
Jon Collins' old age eventually caught up to him and he was euthanized in 1998 at the ripe old age of 36. Pergolide gave Jon Collins a chance to live out his life with energy and in good health, and gave two generations of Rhonda Rayn's family a chance to enjoy his versatile good nature.
Cabby
Cabby is a 20-year-old Morgan type gelding who has been treated for Cushing's disease since 1996. Lois Richerson of Davis, California, purchased him for her daughter Kate. Cabby is a great all-around horse who has been used for endurance, quad drills, jumping and pleasure.
Though Cabby did not show any signs of immune deficiency, he exhibited the classic wooly coat that didn't shed. Since he came from the mountains, his owners figured the thick coat was related to his previous environment. The only other signs he had were some muscle wasting and he seemed a little lethargic. His owners figured the lethargy came from the heavy coat that made him sweat with minimal exercise.
At the suggestion of their neighbor, the late equine geneticist Dr. Ann Bowling, they decided to have their horse evaluated for Cushing's disease by the UC Davis Equine Field Service. Once he was diagnosed, Cabby started treatment with pergolide mesylate and his owners noticed a substantial difference. "We were very happy with the way the medication worked," said owner Lois Richerson. "He is almost back to normal. His muscles filled in, he's perky and he's lost the big shaggy coat."
With the development of the veterinary formulation of pergolide, Lois Richerson said, "Now they have a vet formula in a sweet apple-flavored syrup for horses that costs about 40% less. The pill wasn't a big deal, we just ground it up and mixed it in with his sweet feed, but the cost may be prohibitive for some people. So if there are any people who may not have wanted to treat their horses with pergolide before because of cost, now might be a good time to reconsider. They should check with their local veterinarian. It really made Cabby a new horse."
/ Cabby before treatment for Cushing's disease, showing the classic long shaggy coat that doesn't shed.Cabby after treatment. He now sheds most of his shaggy coat, his energy has improved and his muscle has filled in again. /
Signs of Cushing's Disease
Long, thick, curly coat that may not shed.
Less striking coat changes including a slightly heavier that usual winter coat, late shedding, patchy, slow shedding and growing winter coats earlier than other stablemates, "guard hairs" along the chin or neck in summer.
Increased tendency to founder.
Excessive water drinking and urinating.
Poor wound healing.
More susceptible to infections (abscesses, pneumonia).
Elevated respiratory rates.
Muscle wasting.
Mares may fail to cycle normally or fail to conceive.
Diagnosing and Treating Cushing's Disease
Diagnosed by sampling blood for cortisol levels before and after administration of the steroid dexamethasone.
Treatment once a day with pergolide mesylate. Originally, a human preparation in a pill form was utilized for treating horses. Now, a veterinary formulation of this medication is available which is much more economical and it comes in an apple-flavored syrup.
For information on the veterinary formulation of pergolide, contact: Compound Pharmacy: Prescription Specialities at (800) 861-0933.
Always consult your veterinarian in matters regarding the health of your animals
The research conducted by the Center for Equine Health is supported with funds provided by the Oak Tree Racing Association, the State of California pari-mutuel fund, and contributions by private donors.