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Hyperlipidemia refers to increased levels of circulating triglycerides in the blood. This differs from hyperlipemia which is a specific disease state related to hyperlipidemia. [1]
Hyperlipidemia occurs in any animal that is in a negative energy balance because of decreased feed intake or increased caloric need. This calorie deficit activates a normal physiological process whereby stored fat (lipids) are released into the blood to be used for energy.
The life-threatening condition of hyperlipemia is limited to ponies, miniature horses, and donkeys with insulin resistance. In these animals, blood levels of lipids become high enough to result in liver and renal failure due to excessive accumulation of lipids in these tissues. In severe cases, hyperlipemia can be fatal.
The main sign of hyperlipemia is inappetence, where the animal remains disinterested in food, even after feeds have been reintroduced or any underlying illness is addressed.
If you’re concerned your mini, donkey or pony may be showing signs of hyperlipemia after a period of decreased feed intake, consult with your veterinarian immediately to support their recovery.
Our nutritionists can help you formulate a diet to support your horse’s metabolic health and reduce the risk of this condition.
Hyperlipidemia vs Hyperlipemia
Both these conditions involve elevated levels of circulating fats (lipids) in blood. Hyperlipidemia refers to a natural state whereas hyperlipemia is a specific disease that can be fatal.
Hyperlipidemia
Hyperlipidemia refers to elevated blood lipids that occur during periods of negative energy balance, including:
- Prolonged intervals between meals
- Restricted feeding
- Illness that causes loss of appetite
- Increased energy demand including pregnancy and lactation
In a study of overweight Caspian miniature horses, hyperlipidemia occurred within 48 hours of feed deprivation. [2]
Hyperlipidemia can also occur in horses that are overweight/obese with metabolic disease without a decrease in feed intake. These hyperlipidemic changes are usually mild but can be quite severe on occasion. [11]
Hyperlipemia
As with hyperlipidemia, hyperlipemia develops after fasting, severe illness that suppresses appetite and during an energy crisis associated with pregnancy or lactation.
However, unlike hyperlipidemia, the disease state of lipemia involves accumulation of fat in organs such as the liver and kidney. This can be impair their function and is fatal in severe cases.
Causes of Hyperlipidemia and Hyperlipemia in Horses
Energy deficit
When animals are in negative energy balance they draw on their fat reserves to provide energy to the rest of the body. Fat that is stored in adipose tissue is mobilized and released into the blood as free fatty acids to be delivered to tissues that need cellular energy.
When the mobilization exceeds what the tissues need, the excess free fatty acids are removed by the liver and converted into triglycerides. The triglycerides are released back into blood packaged into large particles called very low density lipoproteins (VLDL). As LDL increases, it can affect metabolic pathways and reduce insulin sensitivity, perpetuating a vicious cycle of fat mobilization and hypertriglyceridemia.
Therefore, hyperlipidemia involves elevated levels of lipids in the form of free fatty acids (released from adipose tissue) and elevated levels of triglycerides (released by the liver in VLDL particles).
This is a normal physiological response that continues until the horse finds food and returns to a positive energy balance.
However, this response can become exaggerated and inappropriate in minis, donkeys and ponies with metabolic syndrome on a severely restricted weight loss diet or that abruptly go off their feed. This is a disease called hyperlipemia. [1]
Metabolic syndrome
In metabolic syndrome, insulin resistance means that the normal suppression of fat breakdown in adipose tissue by insulin is impaired. Therefore, overweight horses with insulin resistance have more abundant fat stores that are more likely to release excess free fatty acids into blood.
Certain drugs tested in horses with metabolic syndrome can also cause hyperlipidemia. For example, SGLT2 inhibitors which cause loss of glucose in the urine create an energy deficit leading to hyperlipidemia and an increase in liver enzymes. [13]
Hospitalization with clinical illness
Horses admitted to equine hospitals are at risk of developing hyperlipidemia. This can occur in any horse that has poor appetite due to their underlying medical condition or as a consequence of the change in environment, feed, and routine.
Of 779 horses admitted to an equine hospital for a variety of reasons including colic, metritis, laminitis and acute renal failure, 13 horses had severe hyperlipidemia. [12]
Pregnancy and lactation
Mares that are pregnant or lactating have prolonged periods of higher energy demands. Compared to non-breeding, maintenance horses, mares in late gestation have 28% higher energy needs and mares in peak lactation have 87% higher energy needs. [16]
Although some mobilization of fat stores and loss of body condition may occur during lactation, excessive mobilization can put them at risk of hyperlipemia. [17]
Genetic susceptibility
The most common breeds likely to have hyperlipidemia that progresses to hyperlipemia are ponies, miniature horses, and donkeys. These breeds may have a genetic predisposition for obesity and metabolic issues. [1][2]
Signs & Symptoms of Hyperlipidemia and Hyperlipemia
Hyperlipidemia typically has no symptoms. [11][12][13]
However, horses with hyperlipemia can show significant signs of illness including:
- Anorexia (no appetite)
- Lethargy and weakness
- Fever (if systemically ill)
- Ataxia (lack of muscle control)
- Depression
- Jaundice
- Abdominal swelling
- Diarrhea
- Dysphagia (difficulty swallowing)
Anorexia is the most common symptom seen in hyperlipemic horses. A horse with hyperlipemia will have zero interest in any food– even their favourite treats.
It is important to remember that not all horses disinterested in their feed have hyperlipemia. Anorexia can also be a sign of other conditions, such as colic and fever.
Similarly, the signs of lipemia are not exclusive to this cond