Last week we discussed Equine Metabolic Syndrome, what it is, and what are some symptoms. Our article explored some discussions you should have with your veterinarian if you suspect your horse might be inflicted with EMS. Today, read more on confirming diagnosis, studying for your H-A, and other considerations for a horse with EMS.
The three criteria that confirm a diagnosis of Equine Metabolic Syndrome:
Insulin Resistance determined by blood tests
Laminitis (multiple episodes)
Obese with abnormal fat deposits
To take care of a horse with EMS, the owner, veterinarian and farrier need to work closely together. The horse needs to be on a strict diet. There are now commercially prepared low-sugar diets for EMS horses and some of these may be appropriate. Generally, a limited amount of grass hay with low sugar-content is the main part of the diet. No lush pasture. No sugar cubes or carrots or apples or commercial high-sugar horse treats. Increased exercise is helpful for weight loss if the horse is not too lame from laminitis. Often the laminitis episodes are relatively mild and the owner may not even be aware of any lameness but the veterinarian and farrier may notice abnormal growth rings or sensitivity in the feet. Radiographs (x-rays) of the feet will determine if the coffin bone has rotated in the hoof and if corrective trimming needs to be done to improve the hoof condition and pain. Your veterinarian may prescribe some pain relief medication such as phenylbutazone (“Bute”) or another pain relief medication. Once the horses lose some weight, they often have fewer bouts of laminitis and they are more energetic. They have been suffering a chronic level of pain with even mild laminitis. With treatment, their feet feel better and they are carrying less weight and they feel frisky again! But it must be remembered that this is a lifelong disease and they will get symptoms again if they are allowed to gain too much weight. They will likely be on a strictly controlled diet for the rest of their lives. EMS is not life-threatening but the episodes of laminitis are the reason many of these horses are euthanized. Doing all we can to keep their weight controlled is the best way to help these horses.
If you are studying for your H-A, we can dig a little deeper into our understanding of EMS. Not only are these horses diagnosed with Insulin Resistance, they also have abnormal fat (adipose) cells that secrete excess cortisol. This is the hormone that is elevated in PPID. But the source of the cortisol in PPID is the adrenal gland which is not being properly regulated by the pituitary gland. The pituitary gland is in the brain and is the “switchboard” for many functions in the body. The Dexamethasone Suppression Test (DST) is one test used to diagnose PPID but the results of this test are normal in an EMS horse. The pituitary gland and the adreanal glands behave normally in EMS. The increased cortisol is coming from the abnormal fat cells. (This is why EMS was once called Peripheral Cushing’s Disease. This is not an accurate term any more but an internet search of the term will result in more sites with informative reading!) The consequences of too high cortisol are the same in both EMS and PPID. These include: propensity to laminitis especially with foot abscesses, immune system suppression (leading to foot abscesses and slow healing of wounds and increased susceptibility to viral, bacterial and fungal diseases and slow recovery from infections), insulin resistance, diabetes mellitus (rare in horses but not unheard of), loss of muscle mass and tone (more common in longstanding PPID cases), infertility, weakness, increased urinating and drinking (PU/PD = polyuria and polydipsia).
Further points to consider:
The tests used to diagnose these diseases are not foolproof. The results can be falsely positive or falsely negative due to a variety of conditions. The season of the year also affects the DST results. While the laboratories that run these tests have taken some seasonal changes in the results into account, the results may still come back “inconclusive.” This is where the veterinarian and the owner need to look at all the information (test results, history, physical examination, breed) and make decisions on treatment and care. It may be advisable to repeat the testing in a different season. Fall is the problematic season (in the northern hemisphere) and it is possible and even likely that the body is responding to signals to get ready for winter. After all, the endocrine system is not static, it responds to the various conditions of a normal, healthy body resulting in different levels of chemicals that we might measure.
To really get you thinking:
It is possible to have both PPID and IR in the same horse. Increased cortisol can cause IR. Remember, the PPID horse usually looks different in age (older) and coat (shaggier) than the EMS horse. So, not all IR horses are EMS horses. But all EMS horses are IR horses because IR is part of the definition of EMS.
Horse and pony breeds that originated in areas with harsh weather conditions are more likely to develop EMS. These breeds include Shetland ponies, Morgan horses, Peruvian Paso horses, to name a few. It is likely that their fat cells are different than other breeds because of the harsher climates where they developed. This is still being researched but it is an interesting point to consider.
If this article has left you more confused than enlightened, welcome to the definition of a “syndrome!” If you would like more study materials or have question, feel free to contact me directly. firstname.lastname@example.org
Our blog article comes to us today from USPC Advisory Board Member and Veterinarian, Rae A Birr, DVM. Rae graduated from Pony Club as a B in 1978 and graduated from Michigan State University as a Veterinarian in 1984. Her practice career has always included horses, particularly equine medicine, reproduction and conditioning. She feels strongly about educating the horse owning public so we can be even better caregivers of our equine partners.