Determining which endocrine disorder is affecting a horse can be more complicated than basing a diagnosis on how a horse looks. Though how a horse appears (fat, shaggy, laminitic) is still an important piece to diagnose, it's no longer the only component a veterinarian will use to determine what ails the equine, reports The Horse.
An accurate diagnosis and treatment can lower the risk of complications arising from endocrine disorders, the most common of which are pituitary pars intermedia dysfunction (PPID, also known as Cushing's disease), insulin dysregulation (ID), and equine metabolic syndrome (EMS).
Adding to the conundrum is that horses can suffer from multiple endocrine disorders at once.
A blood draw is often the first thing a veterinarian will do to narrow down the focus of which metabolic issue the horse is experiencing. Often this test must be sent to an outside laboratory for analysis. To get more-accurate information, a veterinarian may perform a dynamic blood test, where certain parameters are followed and multiple blood samples are drawn, often hours (or days) apart.
Endocrine disorder research is ever evolving, and veterinarians often must strike a balance between new research and their personal experience with disease.
Pituitary pars intermedia dysfunction (PPID)
Pituitary pars intermedia dysfunction (PPID) is an enlargement within the pituitary gland, which affects hormone regulation. The disease can be difficult to discern as its “signs” – like loss of muscle tone, lethargy, and delayed shedding – are often associated with old age and not identified as a sign of possible disease. Horses with more-advanced cases of PPID may drink excessive amounts of water (and urinate more), look potbellied, or have abnormal sweating patterns.
In the past, practitioners have utilized a dexamethasone suppression test to diagnose PPID. This test involves a blood draw, administration of dexamethasone and then another blood draw the next day to compare cortisol levels. While this test can still diagnose late-stage PPID, it is no longer the test of choice among veterinarians.
Now in vogue for a horse with multiple symptoms indicating that it has PPID is taking one blood sample and measuring the baseline ACTH levels. Horses who are younger or who are exhibiting mild signs of PPID can have the TRH (thyrotropin-releasing hormone) stimulation test administered, which gauges ACTH response to a TRH injection.
Though testing is the preferred means of diagnosing a horse's endocrine disorder, starting the horse on PPID medication without a definitive diagnosis is acceptable if the horse is exhibiting signs of PPID and the owner faces financial limitations.
Insulin Dysregulation (ID)
Insulin Dysregulation (ID) occurs when a horse's body produces too much insulin, which can cause regional adiposity, laminitis, and obesity, though the disease can present in myriad ways in affected horses. ID in horses is often diagnosed using an oral sugar test, which is a blood test after the horse is given a high-carbohydrate stimulus like corn syrup.
An OST test can be affected if the horse is fasted, so care should be taken to administer the OST test in the same manner over time. The type of forage a horse is fed can also affect insulin response in OST tests.
Equine Metabolic Syndrome (EMS)
Horses with equine metabolic syndrome (EMS) often have a combination of conditions: they have ID and are fat with a cresty neck and abnormal fat deposits behind the wither, over the back, and near the tailhead. Horses that are gaited or of Spanish lineage are more likely to develop EMS, as are donkeys, Miniature Horses, Morgans, Warmbloods, and some ponies.
Findings from recent studies recommend that horses suspected to have EMS be tested similarly to horses with suspected ID, as well as have genetics and clinical signs considered.
Though many metabolic ills may be able to be diagnosed based on how a horse looks, laboratory diagnostics are imperative to ensuring accurate treatment is established.
Read more at The Horse.
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