Equine metabolic syndrome
In humans, dysfunction of adipose tissue, even in cases without obesity, has been associated with the development of insulin resistance, hypertension, systemic inflammation, and increased risk of blood clots (thrombosis).
The inflammation produced by these hormones are thought to inflame adipose tissue, leading to the production of more adipokines and perpetuation of the cycle, and a constant low-level, pro-inflammatory state.
This is similar to type II diabetes in humans, where the action of insulin is impaired, despite often elevated concentrations.
[2] There does appear to be a strong link between decreased insulin sensitivity in obese animals; however, it is unknown which syndrome is the cause and which is the result.
[7] However, recent research suggests that the situation is more complex, in that "compensated insulin resistance is essentially physiological and health sustaining", and only when this compensatory mechanism fails does laminitis ensue.
[9] Ponies and horse breeds that evolved in relatively harsh environments with only sparse grass, the proverbial "easy keeper", tend to be more prone to EMS and insulin resistance.
This possibly occurred as a survival mechanism, where the animal would lay down fat during plentiful times, such as the spring and summer, and maintain their weight more easily during the harsh, cold seasons.
[1] EMS horses tend to become obese very easily, depositing fat in the crest, shoulders, loin, above the eyes, around the tail head, and the mammary glands or prepuce, even when the rest of the body appears to be in normal condition.
[1] EMS shares similarities to pituitary pars intermedia dysfunction (also known as equine Cushing's disease), which also causes regional adiposity, laminitis, and sometimes insulin resistance.
Other factors, such as stress, feeding, inflammation, or administration of α-2 agonist drugs such as xylazine and detomidine, can falsely raise blood glucose levels.
[13] Insulin normally increases after feeding, as well as secondary to cortisol (stress) and epinephrine (pain), so measurement should be avoided if any of these conditions are present.
[1] Measurement of fasting insulin concentration involves giving a horse a single flake of hay, low in non-structural carbohydrates, at 10 pm the night before testing.
The following morning, karo corn syrup is given orally, and glucose and insulin levels are measured at 60 and 90 minutes after administration.
A similar test is available outside the US, in areas where corn-syrup products are less readily available, where horses are given a morning meal of chaff with dextrose powder, and blood insulin levels are measured 2 hours later.
NSC include starches, single sugars, and fructans, whereas cellulose and hemicelluloses are structural carbohydrates.
However, feeding less than 1% of body weight in forage is not recommended, since secondary problems such as hyperlipemia and stereotypies can occur, and insulin resistance may actually be worsened.
Current recommendations include 2–3 sessions a week, of 20–30 minutes of work, with gradual increase in duration and intensity.
Metformin is a drug used in humans for type II diabetes, and has been shown to improve insulin sensitivity and reduce output of glucose by the liver.
