PATHOLOGY - Equine Obesity Flashcards
What is the ideal body condition score for a horse based on the five point scale?
Based on the five point scale, a body condition of 3 is ideal
Describe a body condition score of 3 in a horse based on the five point scale
You can feel but not see the ribs
Straight neck profile (no neck crest)
Rounded rump without a gutturing effect
What are the benefits of the cresty neck scoring system in horses?
The cresty neck scoring system is more predictive of insulin dysregulation than body condition scoring and thus can be relevant to the diagnosis of equine metabolic syndrome (EMS), and this system can be easily used by owners
What are some of the more common presenting clinical signs of obesity in horses?
Recurrent laminitis
Dyspnoea
Exercise intolerance
Poor performance
What is one of the first things you should determine when presented with an obese horse?
When presented with an obese horse, you should determine if the obesity is uniform or if there are abnormal fat deposits
Which equids are more prone to obesity?
Ponies
Donkeys
Minature equine breeds
How do you manage obesity in horses?
Dietary management
Exercise
Manage any complications of obesity
Which dietary modifications are required for managing obesity in horses?
Low calorie roughage
Soaked roughage
Limit roughage intake
Remove concentrates from the diet
Grazing muzzles if on pasture
Grazing at night if on pasture
What is the ideal roughage to use for managing obesity in horses?
Hay with less than 10% non-structural carbohydrates
Why is it important to soak roughage when managing obesity in horses?
Roughage should be soaked to remove soluble sugars
What do you need to supplement if feeding horses soaked hay to manage obesity?
If you are feeding soaked hay to manage obesity, make sure to supplement them with proteins and water soluble vitamins
What are the benefits of turning out horses at night when trying to manage obesity?
It is beneficial to turn out horses at night when managing obesity as this is when fructan (a non-structural carbohydrate) levels are low due to the lack of photosynthesis at this time
What are the main diseases associated with obesity in horses?
Laminitis
Equine metabolic syndrome (EMS)
Hyperlipaemia
Which diseases should be investigated for in horses with laminitis?
Equine metabolic syndrome (EMS)
Equine pars intermedia dysfunction (PPID)
Insulin Resistance (IR) is the hallmark of EMS. Horses with EMS show reduced sensitivity to insulin, meaning their body requires more insulin to maintain normal blood glucose levels.
Insulin resistance occurs when the body’s cells (especially in muscles and fat) become less responsive to insulin, leading to a reduced ability to absorb glucose from the bloodstream.
Hyperinsulinemia: To compensate for the reduced cellular response, the pancreas secretes more insulin, leading to persistently elevated levels of insulin in the blood.
The persistent high insulin levels contribute to many of the secondary complications of EMS, including obesity, abnormal fat deposition, and an increased risk of laminitis.
2. Obesity and Abnormal Fat Distribution
Obesity is a significant risk factor for EMS, and horses affected by EMS tend to have excessive body fat, particularly in areas such as the neck (cresty neck), shoulders, and back.
In EMS, fat cells (adipocytes) become dysfunctional, leading to altered adipokine secretion. Adipokines are molecules secreted by adipose tissue that regulate energy balance, inflammation, and insulin sensitivity.
Excessive adiposity leads to chronic low-grade inflammation, which can further impair insulin sensitivity. Increased fat deposits in areas like the neck (often called “cresty neck” in EMS horses) and around internal organs contribute to metabolic disturbances and exacerbates insulin resistance.
3. Hormonal Imbalances
Several hormonal abnormalities play a role in the pathophysiology of EMS:
Leptin: Leptin is a hormone secreted by fat cells that helps regulate energy balance. In EMS, despite elevated fat stores, leptin levels are often altered, and the body becomes resistant to its action. This worsens the metabolic dysfunction, contributing to obesity and insulin resistance.
Cortisol: Elevated levels of cortisol (a stress hormone) have been observed in horses with EMS. Chronic stress or increased cortisol can impair insulin sensitivity and contribute to the development of obesity.
Thyroid Hormones: EMS horses may also show subtle abnormalities in thyroid function. Lower thyroid hormone levels (hypothyroidism) could potentially contribute to reduced energy expenditure and obesity. However, thyroid dysfunction is still not fully understood in EMS.
4. Altered Glucose and Lipid Metabolism
Glucose Metabolism: In a healthy horse, insulin helps regulate glucose metabolism by facilitating glucose uptake into cells. However, in EMS, insulin resistance impairs this process, leading to higher glucose levels in the bloodstream. The pancreas compensates by secreting more insulin, resulting in hyperinsulinemia.
Lipolysis: High levels of circulating insulin inhibit lipolysis (fat breakdown), which contributes to excessive fat storage in EMS horses. However, despite this inhibition, these horses often experience abnormal fat mobilization when insulin is less effective.
Hyperlipidemia: In some cases, EMS horses also exhibit elevated blood lipid (fat) levels, including triglycerides and cholesterol, contributing to the metabolic disturbances.
5. Laminitis Risk
One of the most concerning complications of EMS is an increased susceptibility to laminitis, an inflammation of the hoof’s sensitive tissues.
Laminitis is thought to be caused, in part, by elevated insulin levels. The elevated insulin may affect the blood flow to the hoof, increase vascular permeability, and promote inflammation, which can damage the laminae (the tissues that anchor the hoof to the bone).
Laminitis can occur acutely during times of insulin spikes, especially after the consumption of high-carbohydrate feeds (e.g., grass high in sugar or starch), or as a result of metabolic stress.
Horses with EMS are more likely to develop laminitis even in the absence of overt dietary factors or trauma, due to the insulin dysregulation.
6. Genetic Predisposition
EMS appears to have a genetic component, with certain breeds being more predisposed to the syndrome. Ponies, especially those of certain breeds (e.g., Welsh, Shetland), as well as some draft breeds and donkeys, have a higher likelihood of developing EMS.
Genetic factors influencing insulin sensitivity, fat metabolism, and hormonal regulation contribute to the disease’s development, but environmental factors (e.g., diet, exercise, and stress) also play a significant role.
7. Endothelial Dysfunction and Vascular Changes
Endothelial Dysfunction: Elevated insulin levels and chronic obesity can lead to endothelial dysfunction, affecting the blood vessels and impairing their ability to dilate properly. This can contribute to poor circulation and further aggravate the laminitic process.
Vascular Abnormalities: Inflammation and insulin resistance may also alter the blood supply to the hoof, increasing the risk of laminitis, as mentioned.
8. Inflammation
Chronic low-grade inflammation is a key feature of EMS. Adipose tissue in horses with EMS secretes pro-inflammatory cytokines such as TNF-alpha and IL-6, which contribute to insulin resistance and further metabolic dysregulation.
Inflammation can also affect endothelial function and contribute to the pathogenesis of laminitis.
Summary of Key Pathophysiological Elements:
Insulin resistance and hyperinsulinemia lead to impaired glucose and fat metabolism.
Obesity and abnormal fat distribution exacerbate metabolic disturbances and insulin resistance.
Hormonal imbalances (e.g., leptin resistance, cortisol elevation) worsen the syndrome.
Chronic inflammation contributes to insulin resistance and endothelial dysfunction.
The combination of these factors increases the risk of laminitis, one of the most severe outcomes of EMS.
EMS is a complex and multifactorial condition with both genetic and environmental influences, and its management often involves weight management, dietary changes, regular exercise, and, in some cases, medical intervention to improve insulin sensitivity.
