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.

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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 condition. For example, dysphagia is indicative of a nervous system disorder that may be the underlying cause of poor feed intake and lipemia.

If in doubt about your horse’s health, call your veterinarian.

Diagnosis

Your veterinarian will diagnose hyperlipidemia or hyperlipemia after gathering information about your horse’s health history, diet, and condition from a physical exam.

Additionally, they will perform blood work to confirm diagnosis.

In normal horses, triglyceride levels are less than 100 mg/dL. Hyperlipidemia is diagnosed when triglyceride levels are between 100 – 500 mg/dL and without clinical disease. [2] Horses with hyperlipidemia may also have elevated serum liver enzymes.

Blood plasma that is milky white and a triglyceride level of greater than 500 mg/dL (5.6 mmol/L) is consistent with hyperlipemia. [3]

How to Treat Hyperlipidemia or Hyperlipemia in Horses

If you suspect your horse has hyperlipemia, contact your veterinarian immediately.

The goal with both hyperlipidemia and hyperlipemia is to break the cycle of negative energy balance.

Treating hyperlipidemia

Asymptomatic hyperlipidemia is easier to treat since the horses do not lose their appetite.

Energy intake should be encouraged by switching horses on a forage-restricted diet to free choice access to hay. Other soluble fibre sources can also be added. In particular, beet pulp is a highly digestible feed that generates acetate which can be used as an energy source. [18]

Some amino acids, such as glycine, can be converted to glucose to serve as an energy source and help correct the energy deficit. Ensuring the diet has adequate supply of amino acids could help horses with hyperlipidemia. [1]

Treating hyperlipemia

Getting horses with hyperlipemia to eat voluntarily can be extremely difficult. Horses may be fed enterally via nasogastric tube, which is a feeding tube that goes through the nose to the stomach.

Another food replacement method is known as total parenteral nutrition (TPN) and involves bypassing the digestive tract and giving nutrients intravenously. TPN is typically administered in a hospital setting under close monitoring.

Insulin may be administered to your horse to help drive glucose into the cells and discourage fat mobilization. [1] However, this is dangerous as hyperinsulinemia can cause laminitis. [15]

Your veterinarian may also administer fluids to help dilute your horse’s blood and reduce serum triglyceride concentrations. These fluids may contain dextrose, which goes straight into your horse’s circulation to improve energy balance.

Medications may be required to support liver function and reduce inflammation. The anticoagulant heparin activates the enzyme lipoprotein lipase which breaks down triglycerides to remove them from blood.

Prognosis

Hyperlipemia is an extremely serious condition. A review of 23 cases in miniature horses found an overall mortality rate of 39%. [5]

Prompt and veterinarian attention is required to increase your horse’s chance of survival. Typical mortality rates are reported between 43-80% but this can be reduced to 0-33% by aggressive treatment. [1]

Obesity in Horses

With up to 70% of the equine population now classified as overweight or obese, it is common to find horses on a restricted diet to promote weight loss. [6]

However, care must be taken when restricting your horse’s calorie intake. Sudden and aggressive restrictions can lead to hyperlipemia, particularly in minis, ponies and donkeys.

Obesity is the result of a long-term positive energy balance, characterized by the horse consuming more energy than it expends.

Excess energy is stored as fat in adipose tissue around the body. Fat distribution can be internal (such as visceral fat surrounding organs), subcutaneous (under the skin), or regionally, as seen with cresty neck.

With prolonged positive energy balance fat also gets stored in other tissues that are not intended to store fat, such as the liver and muscle. This could contribute to metabolic dysfunction such as insulin resistance in these tissues.

Horses are classified as overweight or obese if they have a body condition score (BCS) of 7-9 on the 9-point Henneke scale, with greater than 20% of bodyweight consisting of fat.

Excessive body fat also results in: [7]

  • Increased strain on joints, tendons, ligaments, and muscles
  • Chronically elevated free cortisol levels [14]
  • Vascular dysfunction in animals with metabolic syndrome

Obesity is also a major risk factor for several other conditions and can contribute to: [7]

  • Cardiovascular issues
  • Hyperthermia (heat stroke)
  • Infertility
  • Poor performance

Some horses have a genetic predisposition to obesity. This includes native ponies, cob-type breeds, draft horses, Haflingers, Arabians, Morgans, miniature horses, and donkeys. [8]

These easy keeper breeds need to have their diets carefully managed to ensure a neutral energy balance is maintained.

Preventing Hyperlipidemia and Hyperlipemia

Hyperlipidemia in horses is largely preventable, given the right feeding and management practices.

Assessing your horse’s individual risk, feeding adequate forage, and closely monitoring body condition are some of the ways that you can reduce the risk of this condition as well as other forms of metabolic dysfunction.

1) Assess your Horse’s Risk Level

The first thing to consider is whether your horse is in a high-risk category for developing hyperlipidemia or hyperlipemia.

Does your horse have a genetic predisposition to hyperlipemia? Answer yes if your horse is one of the following:

  • Miniature horse
  • Donkey
  • Native pony

Is your horse overweight or obese with a body condition score of 7 or greater on a 9-point scale? Does your horse have a metabolic condition including equine metabolic syndrome or insulin resistance caused by PPID?

Has your horse experienced extreme stress? Do they engage in extreme physical exercise (i.e. racehorses post-racing)?

Finally, is your horse in a negative energy balance? Horses at risk of this include:

  • Horses on a restricted diet
  • Sick horses (fever, colic, etc.)
  • Pregnant mares
  • Lactating mares
  • Horses with poor appetite

Once you know your horse’s individual risk profile, you can determine how aggressively you need to adopt the following preventative strategies.

2) Feed Adequate Forage

When dieting your overweight horse, aim for a slow reduction in weight and ensure they receive adequate forage.

Drastic feed restriction results in sustained release of lipids that eventually leads to hyperlipidemia.

Avoid rapid weight loss by aiming for weight loss of around 1% each week. Closely monitor and track your horse’s weight and body condition score on a weekly basis. [9]

Horses should be fed a minimum of 1.5% of their current bodyweight in forage per day, or 2% of their ideal body weight, whichever is larger.

For a 500 kg (1100 lb) horse, this means feeding a minimum of 7.5 kg (16.5 lb) of forage per day.

If you are feeding soaked hay, a mature low-sugar hay or straw, 2% of your horse’s bodyweight could be fed per day to achieve weight loss. [10]

The amount of hay to feed will also depend on the quality of hay (ie its digestible energy content). Submit a forage sample for analysis and consult with an equine nutritionist to determine an appropriate feeding rate for your horse.

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3) Follow The Golden Rules of Feeding

In addition to feeding a forage-first diet, you can also support your horse’s metabolic health by eliminating excess sugars and starches in the diet. Avoid grain-based concentrates and high carbohydrate feeds or balancers, which can worsen insulin resistance.

Provide your horse with many small meals throughout the day rather than intermittently feeding large meals. Intermittent feeding practices can also increase the risk of gastric ulcers.

Feed according to your horse’s workload and bodyweight. A nutritionist can help you calculate your horse’s individual needs.

Finally, make all feeding changes gradually. Horses are particularly sensitive to change. Major alterations in the feeding program can trigger hyperlipidemia if the horse does not eat well or the digestible energy content of the diet changes drastically.

4) Vitamins and Minerals

Overweight horses may require fewer calories in their diet, but they still require the same quantity of vitamins, minerals, and protein as other horses of the same weight and workload.

A concentrated forage balancer that is low in hydrolyzable carbohydrates (HC) or a vitamin and mineral supplement will help meet your horse’s daily requirements without adding unnecessary calories to the diet.

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AminoTrace+ supplies 20 mg of biotin, high levels of natural vitamin E, a full B-vitamin profile as well as added amino acids and 100% organic trace minerals. It comes in a low-HC pellet and is designed to balance the majority of forage- and grain-based diets.

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5) Body Condition Score

When on a restricted diet, it is important to assess your horse’s body condition weekly. A dramatic drop in body condition could indicate anorexia or other health problems.

You should aim to maintain your horse at a body condition score of 4-5 on the 9-point Henneke scale.

6) Seek Professional Help

If your horse is struggling to lose weight, ask your veterinarian to test for metabolic conditions such as EMS and PPID (pituitary pars intermedia dysfunction, aka Cushing’s disease).

Metabolic conditions increase the risk of hyperlipidemia and can make it more difficult to lose weight.

Consult with a nutritionist to design a balanced feeding plan for your horse to support weight loss. You can submit your horse’s information online and our nutritionists can assist you for free.

Conclusion

Hyperlipidemia occurs whenever there is an energy deficit. It can progress to hyperlipemia which is a potentially dangerous, hard to treat condition with a guarded prognosis.

As the prevalence of equine obesity increases, cases are now on the rise. However, this condition is entirely preventable with the right nutrition and management strategies.

For further information, read our article on how to body condition score your horse.

If you would like help formulating a weight reduction feeding program for your horse, submit their information online for a free consultation with our equine nutritionists.

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References

  1. McKenzie, H.C. Equine hyperlipidemias. Veterinary Clinics: Equine Practice. 2011.
  2. Seifi, H.A., Gray, H., Mohri, M. and Badiee, A. Hyperlipidemia in Caspian miniature horses: effects of undernutrition. Journal of Equine Veterinary Science. 2002.
  3. Equine Hyperlipidemia. Horse DVM.
  4. Pösö, A.R., Viljanen‐Tarifa, E., Soveri, T. and Oksanen, H.E. Exercise‐induced transient hyperlipidemia in the racehorse. Journal of Veterinary Medicine Series A. 1989.
  5. Mogg, TD. Palmer, JE. Hyperlipidemia, hyperlipemia, and hepatic lipidosis in American miniature horses: 23 cases (1990-1994). J Am Vet Med Assoc. 1995 Sep 1;207(5):604-7.
  6. Menzies‐Gow, N.J., Harris, P.A. and Elliott, J. Prospective cohort study evaluating risk factors for the development of pasture‐associated laminitis in the United Kingdom. Equine veterinary journal. 2017.
  7. Rendle, D., McGregor Argo, C., Bowen, M., Carslake, H., German, A., Harris, P., Knowles, E., Menzies-Gow, N. and Morgan, R. Equine obesity: current perspectives. UK-Vet Equine. 2018.
  8. Harris, P.A., Bamford, N.J. and Bailey, S.R. Equine metabolic syndrome: evolution of understanding over two decades: a personal perspective. Animal Production Science. 2020.
  9. King, C. and Mansmann, R.A. Preventing laminitis in horses: dietary strategies for horse owners. Clinical Techniques in Equine Practice. 2004.
  10. McGowan, C.M. et al. Dietary restriction in combination with a nutraceutical supplement for the management of equine metabolic syndrome in horses. The Veterinary Journal. 2013.
  11. Dunkel, B. et al. Severe hypertriglyceridaemia in horses and ponies with endocrine disorders. Equine Vet J. 2014.
  12. Dunkel, B. and McKenzie III, H.C. Severe hypertriglyceridaemia in clinically ill horses: diagnosis, treatment and outcome. Equine Vet J. 2003.
  13. Kellon, E.M. and Gustafson, K.M. Hypertriglyceridemia in equines with refractory hyperinsulinemia treated with SGLT2 inhibitors. Open Vet J. 2023.
  14. Hart, K.A. et al. Effect of Age, Season, Body Condition, and Endocrine Status on Serum Free Cortisol Fraction and Insulin Concentration in Horses. J Vet Intern Med. 2016.
  15. de Laat, M.A. et al. Hyperinsulinemic laminitis. Vet Clin North Am Equine Pract. 2010.
  16. National Research Council Nutrient Requirements of Horses: Sixth Revised Edition. 2007.
  17. Lawrence, L. Feeding Stallions and Broodmares. Equine Applied and Clinical Nutrition: Health, Welfare and Performance. 2013.
  18. Sunvold, G.D. et al. In vitro fermentation of cellulose, beet pulp, citrus pulp, and citrus pectin using fecal inoculum from cats, dogs, horses, humans, and pigs and ruminal fluid from cattle. J Anim Sci. 1995.