NOTE! This article is on Laminitis. Laminitis is often confused with Founder. Laminitis and Founder are two different conditions, not synonyms. We recommend reading our full series on laminitis before moving on to learning about founder.
Laminitis 101 Recap
If you missed our “Laminitis 101” article (which we recommend reading), here is a brief recap on laminitis.
The word laminitis means “inflammation of the laminae”, and it is a systematic condition that affects the whole horse, not just its feet.
Laminitis can be incredibly painful and can become life-threatening if not promptly addressed.
While laminitis affects many systems within the horse’s body, the hooves are most severely impacted by this condition: laminitis causes inflammation of the laminae - the tissues connecting the hoof wall to underlying structures such as the coffin bone.
Laminitis can lead to founder, the rotation or sinking of the coffin bone, a potentially fatal condition.
The many causes of laminitis
This article delves into all known causes of laminitis, categorizing them into four major groups: metabolic or endocrine-related causes, mechanical or physical stresses, infectious or inflammatory causes, and toxic or nutritional causes.
Each of these categories represents a distinct set of underlying mechanisms that can trigger laminitis.
Metabolicand Endocrine Disorders
1.Equine Metabolic Syndrome (EMS)
Equine Metabolic Syndrome(EMS) is a major cause of laminitis, particularly in ponies, Arabians, and certain breeds predisposed to obesity and insulin resistance. EMS is characterized by:
Insulin resistance: The horse's body becomes less responsive to insulin, which results in elevated levels of circulating insulin (hyperinsulinemia).
Hyperglycemia: Increased blood glucose levels, though less common in horses than in humans, can occur in some EMS-affected horses.
Obesity: A higher percentage of body fat, especially in the neck and crest, is a typical feature of EMS.
Horses with EMS are predisposed to laminitis for several reasons. Excessive amounts of fat can lead to systemic inflammation, which can be additionally exacerbated by increased blood glucose levels. Recent studies are also pointing to the fact that high levels of insulin are likely toxic to the sensitive laminae inside the hoof.
2. Cushing’s Disease (Pituitary Pars Intermedia Dysfunction - PPID)
Cushing’s Disease, or Pituitary Pars Intermedia Dysfunction (PPID), is an endocrine disorder that affects older horses and is caused by a dysfunction in the pituitary gland, leading to excessive production of hormones like cortisol. Elevated cortisol levels can:
Increase blood sugar levels.
Decrease insulin sensitivity, further contributing to insulin resistance.
Alter blood flow, which negatively affects the laminae.
Horses with PPID are more prone to laminitis, especially during the late spring and summer months when pastures contain higher levels of non-structural carbohydrates (NSCs). This is why PPID is considered a significant risk factor for laminitis in older horses.
3. Insulin Dysregulation and Hyperinsulinemia
Horses with insulin dysregulation, a condition often associated with EMS and PPID, have higher levels of insulin circulating in the blood.
Insulin, in excess, can have a direct impact on the laminae. It is believed that high levels of insulin may cause vasoconstriction (narrowing of blood vessels), which decreases blood flow to the hooves and impairs the normal function of the laminae.
4. Hyperthyroidism
Hyperthyroidism, though rare in horses, can also contribute to laminitis. The thyroid gland's overproduction of thyroid hormones can lead to metabolic disturbances and insulin resistance, increasing the risk of laminitis.
Mechanical and Physical Causes
1.Overloading of the Hoof
Mechanical stress on the hooves from overwork and excessive weight-bearing can lead to laminitis. This is commonly seen in:
Obese horses: Extra body weight places more stress on the hooves.
Working horses: Excessive exercise, particularly on hard surfaces, can lead to fatigue and trauma of the laminae. This is sometimes called “road founder”.
2. Trauma, Injury, and Medications
Any injury or traumatic event causing inflammation can lead to laminitis.
Injury in one limb can cause laminitis in the supporting limb, which will have to support excessive weight.
Additionally, certain medications to treat unrelated conditions are known to increase the risk of laminitis in some horses.
Infectious and Systemic Causes
1.Sepsis and Systemic Infections
Laminitis is often a secondary complication of sepsis (a systemic infection), particularly in the case of severe illness or injury.
When a horse suffers from systemic infection, such as endotoxemia (toxins in the blood), the inflammatory response can cause laminitis.
Endotoxins: These are harmful substances released from bacteria, particularly Gram-negative bacteria. When they enter the bloodstream, they can trigger a cascade of events that lead to inflammation and damage in the laminae. Endotoxemia is a common consequence of conditions like colic, pneumonia, or severe gastrointestinal disease.
Septicemia: Infections that spread through the bloodstream can lead to a similar inflammatory response.
2. Colic and Gastrointestinal Disturbances
Colic and gastrointestinal issues, particularly those involving significant gut microbiome disruption, can result in endotoxemia and trigger laminitis. Horses with severe colic, especially those that experience bowel strangulation or necrosis, are at high risk for developing laminitis due to the release of endotoxins from damaged tissues.
Toxic and Nutritional Causes Grain or High-Sugar Diets (Carbohydrate Overload)
1. Grain or High-Sugar Diets (Carbohydrate Overload)
Feeding a horse excessive amounts of concentrates, grains, or lush pasture that is high in non-structural carbohydrates (NSCs) is one of the most common nutritional causes of laminitis.
When a horse consumes an excessive amount of sugar or starch, the excess carbohydrates can:
Disrupt the gut’s normal function, leading to the fermentation of sugars in the colon.
Cause the release of endotoxins into the bloodstream, which can result in laminitis.
Lead to insulin resistance and metabolic changes, which can further exacerbate the risk.
Colic and gastrointestinal issues, particularly those involving significant gut microbiome disruption, can result in endotoxemia and trigger laminitis. Horses with severe colic, especially those that experience bowel strangulation or necrosis, are at high risk for developing laminitis due to the release of endotoxins from damaged tissues.
This phenomenon is particularly common in horses with a predisposition to metabolic disorders like EMS and PPID. It's most frequently seen in horses fed diets high in grain or rich pasture, especially in spring when the grass is lush and contains higher sugar content.
2. Black Walnut Toxicity
Exposure to black walnut (Juglans nigra) shavings or sawdust in bedding material is a well-documented cause of laminitis.
The ingestion or inhalation of black walnut dust or exposure to it through bedding can lead to the release of toxic compounds that cause inflammation in the laminae, leading to laminitis. Symptoms often appear within 12 to 24 hours of exposure and include severe lameness.
3. Other Toxic Plants
While black walnut is the most common plant-related cause of laminitis, other toxic plants can also contribute. For instance:
Yew: The ingestion of yew plants (Taxus spp.) can result in sudden laminitis, especially when the plant material is consumed in large quantities.
Oleander: Toxicity from this plant can also result in laminitis as part of the systemic effects.
Other Contributing Factors
1. Genetic Predisposition
Certain breeds and individual horses are more genetically predisposed to developing laminitis, particularly in the context of metabolic disorders.
Breeds such as ponies, Morgans, Arabians, and some draft horses are more susceptible to developing insulin resistance, EMS, and PPID, all of which increase the risk of laminitis.
2. Age and Hormonal Factors
Older horses, especially those over the age of 15, are more prone to developing laminitis, particularly if they have underlying conditions like PPID or EMS.
Hormonal changes, such as those seen in postfoaling mares, can also increase the risk of laminitis.
Prevention
Prevention of laminitis involves addressing risk factors such as managing body weight, controlling carbohydrate intake, regular hoof care, and monitoring for metabolic and endocrine disorders.
Early diagnosis and intervention are key to preventing long-term damage and ensuring the best outcomes for horses affected by this serious condition.
If you suspect a horse may be at risk or is showing signs of laminitis, it is important to consult with a veterinarian for a thorough diagnosis and tailored management plan.
Read Laminitis 103 next!
Self Assessment Quiz
Multiple Choice Questions
Which metabolic disorder is a major cause of laminitis, particularly in ponies and certain breeds?
a) Hyperthyroidism
b) Equine Metabolic Syndrome (EMS)
c) Cushing’s Disease (PPID)
d) B and C
How does insulin resistance contribute to laminitis?
a) It causes direct trauma to the hoof wall
b) It increases fat deposits in the hooves
c) It leads to high levels of circulating insulin, which may be toxic to the laminae
d) It thickens the hoof wall, causing inflammation
What is "road founder"?
a) Laminitis caused by excessive exercise on hard surfaces
b) A type of genetic laminitis
c) A bacterial infection of the hoof
d) A condition where the horse’s hoof grows abnormally
Which of the following toxins is specifically linked to laminitis when found in horse bedding?a) Yew
b) Black walnut
c) Oleander
d) Red maple
True or False
___ Cushing’s Disease (PPID) only affects younger horses and is not a concern for older horses.
___ Endotoxemia from bacterial infections can contribute to laminitis by triggering systemic inflammation.
___ Obese horses are at a higher risk of developing laminitis due to increased stress on their hooves and metabolic disturbances.
___ Horses that consume high amounts of non-structural carbohydrates (NSCs), such as grains and lush pasture, have a lower risk of developing laminitis.
Short Answer Questions
Explain how colic or gastrointestinal disturbances can lead to laminitis.
Describe the role of genetic predisposition in a horse’s risk of developing laminitis and name at least two breeds that are more susceptible.
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