Equine Medical Service
3021 W. County Rd. 64
Fort Collins, CO 80524
Office
(970) 568-9445
FAX
(970) 568-0705
| Equine Medical Service Advantage Program | |
| |
| 
|
There many concerns which are unique to our older patients. For example, older horses are more likely to develop cancer, or neoplasia, than their younger counter parts. There are several types of neoplasia to which older horses are predisposed. Their effect on the horse may be minimal or severe depending on the type of cancer and location. Tumors, which have the ability to spread, or metastasize, are of much more concern than benign tumors, which tend not to be invasive.
Melanomas are common in middle age and elderly grey horses. An estimated 80% of grey horses over 15 years of age have melanomas. These tumors most commonly occur under the tail and in the region around the anus. Melanomas may form in clusters or be solitary. They may increase in size slowly as the horse ages. Fortunately, in grey horses it is uncommon for melanomas to metastasize and for this reason they usually are not biopsied or removed. However, melanomas may cause a physical interference with defecation or urination, which necessitates their removal. Although it is uncommon, melanomas in grey horses may be benign for many years and suddenly become aggressive and metastasize. In nongrey (bay, chestnut, black, etc) horses, melanomas are much more likely to metastasize and biopsy is usually warranted.
Old horses may develop thyroid adenomas, which cause the thyroid gland to become larger and more prominent. The owner may be able to feel both lobes of the thyroid in the throatlatch region. Sometimes these are mistaken for swollen lymph nodes. In the horse, thyroid adenomas are rarely functional. This means they do not produce increased thyroid hormone and there in no adverse effect in the horse.
Older horses frequently develop lipomas . These are benign fatty tumors. If you have an old dog, they may have lipomas under their skin. In horses, lipomas most commonly form in the mesentery of their intestines. They do not metastasize. We believe many old horses have lipomas which are never a problem. Unfortunately, some lipomas may cause colic due to their physical location. Lipomas which form a simple obstruction tend to result in chronic colic. Lipomas which wrap around and strangulate intestines can cause severe acute colic and serious damage to the intestines. Treatment for lipomas requires surgical removal of the tumor. During surgery, the health of the intestine can be assessed. This is a major factor for the surgeon when considering a prognosis.
A type of neoplasia many owners are familiar with is pituitary adenoma because is causes Cushing Syndrome, if the tumor is functional. A functional pituitary adenoma produces the hormone ACTH which induces the adrenal glands to produce excess amounts of cortisol. Excess cortisol has many effects on the horse, including the characteristic long curly hair coat. However, 15% of horses with Cushing's do not have a long hair coat. They may have more subtle coat abnormalities which may be difficult to appreciate such as delayed shedding, long hairs only in the jugular furrow, or long chin hairs. Excess cortisol also suppresses the immune system, causes muscle wasting, increased water consumption and urination, increased sweating, and predisposes the horse to laminitis. Due to the potential for multiple and serious effects, treatment should be considered.
We frequently suspect serious forms of cancer in old horses that are losing weight or doing poorly for no apparent reason. Many diagnostic techniques commonly used in humans or small animals such as abdominal or chest radiographs, MRI, CAT, ultrasound, nuclear scans, etc are often prohibitively expensive, unavailable for horses, or not powerful enough to reveal tumors in a body as massive as a horse's. Blood work can sometimes hint at cancer. We may be able to feel intestinal tumors via rectal palpation. Ultrasound, sometimes combined with a standing biopsy, can be used to evaluate the liver. Scopes are very useful in evaluating the esophagus and stomach. Standing laparoscopy can provide a method of exploring the abdominal cavity and a means of obtaining biopsy samples. With abdominal taps we may obtain fluid for analysis which contains cancer cells. Even with these techniques, we frequently can not obtain a definitive diagnosis and are often forced to make a presumptive diagnosis of cancer in a poor doing old horse.
This article is one in a series addressing common issues of the ageing equine athlete. Look for additional information on maintaining the "Geriatric" horse in future newsletters.
