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Equine Hyperlipaemia
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Introduction
Hyperlipaemia is an important condition in ponies and donkeys, not just because of the seriousness of the clinical signs and biochemical changes involved, but because of the distress it causes owners and breeders that have had animals suffer from it.
Hyperlipaemia occurs most commonly in fat animals in late pregnancy and is rarely seen in larger horses. The syndrome has similarities with conditions in other species but the definitive aetiologies are not yet known. The condition in ponies is undoubtedly related to stress. The biochemical mechanisms involved in equine hyperlipaemia are considered and an hypothesis of possible pathogenesis is put forward. This hypothesis is tested by presenting the results of a preliminary study to evaluate glucose and lipid metabolism in horses and ponies. It appears that the pony is markedly insensitive to insulin compared to larger horses which means that triglycerides are more readily mobilised and the animal is therefore susceptible to hyperlipaemia in a situation of negative energy balance. The effect of stress is to increase cortisol levels which only exacerbates the insulin insensitivity and so creates a vicious circle. The importance of an innate insulin insensitivity may also be important in the pathogenesis of such conditions as laminitis.
Donkeys (photo: the donkey sanctuary)
What is happening?
When the donkey stops eating enough, the essential organs still require a food supply, so the body tries to use the energy that is stored as fat deposits. The result is that free fatty acids are circulated to the liver to be converted to glucose for use by the body. This system is controlled by complex hormonal events, which should shut down the amount of fat released from fat stores as the liver produces the glucose for the body.
Sadly donkeys and small ponies are not able to efficiently turn off the fat release and the blood soon fills up with excess fat in circulation. This circulating fat can be measured in the blood as triglycerides by your veterinary surgeon.
Large amounts of fat cause the liver and kidneys to degenerate and fail, and eventually all the organs in the body fail, this results in irreversible damage and death follows soon after.
Risk factors
• Donkeys.
• Small pony breeds eg Shetlands, Welsh Mountain, Miniatures. Uncommon in horse breeds, but has been reported.
• Females more than stallions/geldings (only partly due to pregnancy and lactation).
• Obesity.
• Stress (transport, weather, disease).
• Age: increased risk with age. Age related decline in insulin sensitivity. Unusual < 18 months.
• Underlying primary disease (parasites, enteritis, colitis, impaction, dysphagia, choke, dental problems, lymphosarcoma, etc.).
• Hyperadrenocorticism (Cushing's disease).
• Laminitis.
• Metritis, Hepatopathy, Peritonitis.
Clinical signs
Dull, depressed, anorexic, pyrexic, tachycardia, tachypnoea, gut stasis (dry mucous covered faeces), ataxia, oedema, congested mucous membranes, halitosis, hepatic encephalopathy, 'sham' eating and drinking. Later there may be ventral oedema, and signs of liver and kidney failure such as head pressing, circling and ataxia.
Diagnosis
Your vet should take blood samples early in clinical examination. A diagnosis of hyperlipaemia is confirmed by a plasma triglyceride concentration and the hepatic and renal damage/function.
Treatment
1. Prompt treatment is essential where diagnosis possible. Consider parasites in all cases. Wean foals early.
2. Fluid therapy.
3. Symptomatic therapy: anti-inflammatories, anti-gastric ulcer therapy, multivitamins, anabolics, plasma transfusions, antibiotics.
4. Nutritional support: maintain a positive energy balance. If the animal is very sick your vet may need to provide energy to the donkey via a stomach tube or intravenous therapy.
5. Normalis lipid metabolism with insulin, glucose and/or heparin.
• It is always contra-indicated to use glucocorticoids.
• Keep companions together.
• Assess likely 'stress' of hospitalising patient, may prefer to treat at home.
• Owner attitude is vital: if they are willing to hand feed, oral drench and administer oral medicins, the prognosis will be much better.
• Always encourage and try to maintain voluntary feed intake.
• Discuss finances early in disease.
Prognosis
The condition has a high mortality rate (including euthanasia) of between 60 and 100 per cent, and a reported prevalence of between 5 and 11 per cent in ponies and 18 per cent in donkeys in referral hospital populations. In view of the poor prognosis, it highlights the importance of client education in disease prevention.
More about donkeys and hyperlipaemia: The Donkey Sanctuary
