Equine Metabolic Syndrome
Rebecca Hamilton-Fletcher MRCVS
This veterinary feature was first published in Horse & Hound 12 May 2005
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Some ponies seem to get grossly overweight on nothing but fresh air and new thinking suggests that a condition called Equine Metabolic Syndrome may be responsible Anyone who has owned a native pony will be familiar with its ability to create fat out of thin air, and with the difficulties in management this causes. Now at last, as a result of work done at the University of Missouri, a condition called Equine Metabolic Syndrome (EMS) has been recognised.
This condition may explain why domesticated ponies are so prone to obesity and laminitis, and is possibly the result of evolutionary developments that enable native breeds to survive harsh weather and food shortages.In the wild, ponies are programmed to put on weight during the relatively lush summer and autumn months, with fat (stores of energy) distributed around the body in preparation for leaner times. Significantly, fat is preferentially laid down in the abdomen, where it is known as omental fat.Until recently, it was thought that these fat cells (known as adipocytes) were just benign stores of energy. But research has shown that adipocytes are in fact active and can produce a variety of hormones known as adipokines. These help control and regulate a number of body processes and are programmed towards enhancing our native ponies’ ability to endure periods of environmental harshness.It appears that the omental adipocytes produce an especially significant range of adipokines that, among other things, generate an increase in the level of circulating cortisol. This steroid is instrumental in inhibiting the action of the hormone insulin (which controls blood glucose levels), and results in insulin resistance and a degree of hyperglycaemia.
In relatively fat ponies entering the winter months, this insulin resistance has a physiological benefit. It preserves and prioritises glucose (and therefore energy) for essential areas such as the brain, at the expense of non-essential tissues like muscle.As the pony gradually loses weight during the winter, so the level of omental fat reduces and the state of insulin resistance becomes reversed. Eventually, spring arrives and the pony is in a lean but healthy condition — ready to indulge safely in the pleasures of rich grazing.
Unfortunately, this system has become unbalanced as a result of domestication. It has meant that the average equine diet is too rich and too plentiful. Grain-based feeds tend to be the main culprit, but even hay and other forages are now made from improved pastures and so have a high nutritional value.Many ponies enter the winter in an over-fat state and maintain this level of condition, so the state of insulin resistance is not reversed. Long-term insulin resistance has various undesirable consequences, which include chronic hypoglycaemia and hyperinsulinaemia (high blood glucose and insulin levels respectively). Ultimately, a condition of glucotoxicity (too much sugar) arises and this significantly increases the risks of laminitis developing.
“Metabolic syndrome” has been used to describe this scenario. It is well recognised in humans, where there is a very obvious link between obesity and cardio-vascular disease. Human glucotoxicity causes an increase in blood pressure (hypertension), which predisposes to coronary disease — and also insulin-dependent diabetes mellitus (due to the exhaustion of the pancreas’s insulin-secreting abilities).It is thought that hypertension in ponies could predispose them to laminitis rather than heart disease — and a state of diabetes mellitus is recognised but tends to be insulin-dependent because there is no evidence that the pancreas becomes exhausted.
EMS has many characteristics similar to Cushing’s disease, which is why it has often been termed “peripheral Cushing’s disease”. However, this is misleading because there is nothing wrong with the pituitary or adrenal glands in cases of EMS, as there is with Cushing’s. Referring to it as the “laminitis-hypothyroidism syndrome” is also inaccurate because there is no evidence of any thyroid malfunction. Other names include “obesity-related laminitis”, “equine syndrome X” and “insulin resistance syndrome” — but EMS is now universally preferred.
EMS can be difficult to recognise because the signs are often very subtle and it can be confused with Cushing’s or even hyperthyroidism. In general, EMS is seen in ponies, cobs and warmbloods under 15 years of age, whereas Cushing’s tends to affect older equines of any age. Common signs of EMS Obese adult horse (although a minority may be normal sized) Abnormal body fat distribution, eg thickened, cresty neck; excess fat around head of tail; fatty shoulders; flabby, fatty sheath; pot-bellied look“Good doer” who puts on weight easily and loses it with great difficultyUnexplained laminitis that may be obvious and severe or very subtle, eg abnormal hoof growth; laminitic rings on hoof wall and expansion of white line with no apparent lameness; Ravenously hungry all the time; Urinating frequently; Lethargic and lazy; Infertile or abnormal cycles in mares.
There is no one test for EMS. Raised blood glucose is strongly suggestive, especially if the animal is under the age of 15 and showing some of the signs listed. Occasionally, ultrasonography can be helpful in assessing levels of omental fat. Often, a diagnosis of EMS is made only after elimination of similar conditions such as Cushing’s and hyperthyroidism (overproduction of thyroid hormones) from blood tests, for example, glucose tolerance and dexamethasone suppression tests.
Various forms of treatment have been tried, based upon products that influence the pituitary and/or adrenal glands. But there is little rationale behind this because in EMS the pituitary and adrenal glands function normally. The results of trials have been inconclusive so far. Similarly, the reasoning behind the practice of thyroid supplementation for EMS, which is popular in the USA, is weak because these animals are not hypothyroid. It may be that it helps simply because it encourages weight loss. By far the most important aspect of controlling EMS is a combination of diet and exercise. A diet high in fibre and based on hay, non-molassed sugar beet and commercial products such as HiFi Lite is “good”. Sadly, grass, cereals and succulents such as apples and carrots are “bad”. Supplements containing antioxidants, chromium and magnesium claim to be of help (possibly by increasing insulin sensitivity), but more work needs to be done here. Exercise is essential — not only does it encourage a loss in omental fat, but it also promotes an increase in glucose uptake. Work has shown that a fit pony (even if slightly overweight) will have an increased sensitivity to insulin and will lose weight faster than an unfit animal.
January 18, 2008 at 12:57 am
Have short/heavy 15 yo AQHA mare properly shod with wide web shoes w/ sole pressure relief and side clips. Has chronic unilateral lameness w/”playing piano” movement worsened as foot grows out. More pronounced with turning. Occasionally points toe. Appears to want to place weight on heel vs toe. Does have white line issue and evidence of traumatic shoeing injury from previous farrier. Exaggerated startle response. Could live on air alone. I have researched navicular syndrome, metabolic syndrome, hyperthyroidism, white line disease, chronic subclinical laminitis, etc. Horse has done little work, never bred, is a pasture ornament (turnout managed so no lush grass exposure). Has had no known “events” associated with provoking laminitis but subtle signs on trims. Will be consulting vet soon but appreciate any comments. Thanks. Debbie
February 6, 2008 at 11:15 pm
Hi Debbie,
In general, a unilateral lameness will not be metabolic in origin. A unilateral lameness is almost certain to be mechanical in origin, meaning, it’s the trim.
Not to say that he isn’t metabolic and shouldn’t have his diet and lifestyle monitored, but you definitely need an expert opinion on his hoof form. I suggest you search on the websites that list qualified trimmers, or you can email me photos for a consultation and possible recommendation. The email is listed under ‘contact us’.
Good luck
October 21, 2008 at 12:46 pm
I have a 14 year old Cleveland Bay X mare, only 15.3hh but very solid and always has been. Walks past the feed room and puts on weight! Started off around 4 months ago being sore in one fore foot, now sore all round, vet says not laminitis but I’m in regional Australia and don’t have access to another vet until I can get her on the float and take her to the city (she has some floating issues at the moment, accident related). No heat or pulse in her feet, the feet were quite long (I know, terrible, awful me) but have trimmed them progressively over the past week and have seen some improvement in her soundness. She is cresty and has a gutter down her back, with a big belly (looks pregnant with twins). The other thing that rang alarm bells was reading elsewhere about the teats in mares being swollen, the area just in front of her teats has noticeably swollen in the past month. Would be interested to find out what you think? Any help I can get at this stage until I can get her to a decent vet in the city would be brilliant. Emma
October 21, 2008 at 6:41 pm
Hi Emma,
It’s hard of course to say whether your mare’s lameness is a result of mechanical problems or metabolic ones. It sounds like you might be on the right track with the trimming. Nevertheless your mare clearly has issues of a metabolic nature (weight, crestiness, false lactation, etc.). You definitely need to have this looked into, taking blood tests and checking insulin and thyroid levels. In the meantime consider a supplement that contains magnesium and B vitamins, such as Remission available in the US. I’m sure there is something comparable in Oz. Good luck.
October 30, 2008 at 9:53 pm
Thank you ever so much for your reply! Well it’s been a week and I have already seen marked improvement in my mare (Priscilla). I have now been able to trim her feet right down (a long process as she is still sore and doesn’t like to put excess weight on her back feet when I am doing the front ones) and she is in a small yard where the feed has very little substance to it. She is being fed stalky hay twice a day. I have not been able to track down a supplement yet, but when I do she will get this also. The best thing is, she can walk! I’ve been taking her out for daily strolls (on line) to try and get some more weight off her and she is almost sound at the walk, even on hard ground. She even offered a trot yesterday when she got stroppy! It was a shuffly trot and only lasted a few strides, but she offered it so I figure she felt reasonably comfortable to do it. Hopefully she will continue to progress as well as she is at the moment. Thankyou again for your advice! Emma (and Priscilla)
January 23, 2009 at 5:08 pm
Hi! I have a 26 year old Morgan. He has been on Thyroid Medication for years, and is tested a few times a year. He has been a jumper all his life and has remained very fit! Altough fit, has never been what you called “lean”. Definetly a little chub!
The start of this winter, we noticed he was putting on ALOT of weight. I cut out all treats other than carrots, and the vet diagnosed him with EMS. He is on the Metaboleeze supplement, and we are not seeing any results, maybe even gaining more weight. He had been lame for quite some time, but still riding 4 days a week (not hard), to help get some weight off.
Other than cutting out his grain completely, do you suggest keeping him on Metaboleeze? Or do you recommend a different supplement?
Note: Has been on Metaboleeze for almost 2 months.
January 24, 2009 at 10:28 pm
Hi, I have never heard of Metaboleeze before but a quick search shows that it seems to be more for tying up and preventing fatigue after hard exercise. Maybe you could try some of the supplements designed for IR that also contain magnesium, such as Remission. Good luck.
May 22, 2009 at 6:15 am
I just had my horse diagnosed today with EMS. The vet claimed he could have had this for years since he has a cresty neck. My horse is morgan and has had that neck since a yearling. I have been unable to find any info on how this disease effects other areas of the body. My horse also has had suspention ligaments completely fail and is now bone on bone in entire back leg. He is post legged now due to this and he used to be a haler horse! We did geld him a month ago so he did have big hormone changes as well. No founder issues at all-just ligaments issues and hock failure. Is there a coaltion with this?
May 24, 2009 at 1:57 am
Hi Tanya, what you describe is possible EMS and possible DSLD (suspensory ligament failure). I am not aware of any correlation between these two conditions but that does not mean it’s not possible. If your horse has been a stallion for many years I would attribute the cresty neck to being a stallion sooner than a symptom of EMS, especially since he has shown it since one year of age. Usually metabolic symptoms such as cresty neck do not manifest that early in life.
The primary system that is affected by EMS is the metabolic system (endocrine, glands, liver, skin, hooves, etc.) and this can lead to such things as laminitis/founder as a result of Insulin Resistance or Cushings disease.
However from your description I think your greater concern is the connective tissue breakdown. Having said that you might want to test for insulin resistance to rule it out (as Morgans can be very prone to this) and perhaps consider adding a magnesium supplement.
June 28, 2009 at 2:04 pm
Is Remission okay to give to a pregnant mare? I don’t see anything in the ingredients that look to be a problem, but also see where the product is not approved for use in pregnant mares.
June 28, 2009 at 5:04 pm
I wouldn’t add anything to a pregnant mare’s diet without first checking with a vet or nutritionist you trust.