The geriatric horse commonly suffers medical problems presenting with non-specific clinical signs such as poor bodily condition or a depressed mental attitude. The opportunity to investigate and treat these cases has lead to many remarkable instances of ‘coffin-dodging’, most notably as a result of ‘high-tech’ dentistry, nutritional advice and the diagnosis and treatment of endocrinopathies, hepatopathies and enteropathies. Lack of significant abnormality on a blood sample from a thin elderly horse gives the confidence to approach the case as a dietary/dental condition rather than a major internal medical problem.
Clinically healthy geriatric horses and ponies actually show remarkably few significant differences from their younger counterparts. Analysis of blood results from ‘health checks’ on apparently normal horses and ponies at the LEH laboratory suggests that geriatric horses tend to have slightly lower red cell counts and albumen concentration and slightly higher white cell counts and total globulins. However, there is considerable individual variation making these generalisations not very useful.
The commonest abnormalities detected in blood samples taken from geriatric horses with clinical problems are anaemia, hypoalbumenaemia, hyperglobulinaemia and elevations in serum enzymes, most notably GGT and AP. Anaemia in elderly horses is almost invariably mild and poorly regenerative as a result of a chronic inflammatory process and/or malnutrition. Anaemia is rarely the horse’s primary problem and usually indicates an underlying cause. Mild neutrophilia is often seen in cases of marked dental disease and also in many cases of equine Cushing’s disease and neoplasia (especially lymphoma). Lymphopaenia, another typical finding in equine Cushing’s disease, may also indicate a stress response in generally debilitated and/or malnourished horses. Albumen concentration is a key diagnostic factor in weight loss assessment in any age of horse. Profound hypoalbumenaemia (<20 g/l) is almost invariably indicative of protein-losing enteropathy (eg. larval cyathostomosis or alimentary lymphoma) whereas mild hypoalbumenaemia may also indicate hepatopathy or malnutrition. Hyperglobulinaemia as well as indicating chronic infective challenge is commonly seen in cases of hepatopathy and also sometimes neoplasia. GGT remains the most sensitive indicator of hepatopathy in common usage. Modest elevations of GGT (eg 50-90iu/l) might simply indicate a degree of hepatic lipidosis (secondary to Cushing’s disease) or age related mild hepatopathy and are usually insignificant although values greater than 100 iu/l should probably be taken more seriously. AP although not a tissue-specific enzyme, is raised in the majority of enteropathy and hepatopathy cases and is the only enzymatic indicator of intestinal damage.
Clearly many other laboratory parameters and tests may be useful in individual cases and profiles are adaptable to individual situations. Testing for equine Cushing’s disease remains a common clinical dilemma with a multitude of potential choices of test available, none of which are absolutely sensitive or specific. However, the ‘overnight dexamethasone suppression test’ appears to produce highly reliable results although false positives and negatives are still occasionally found.
© The Liphook Equine Hospital 2009
