Page 792 - The Veterinary Care of the Horse

intake to meet their nutritional requirements, causing body fat stores to be mobilized.

Excessive amounts of fat may be deposited in the liver and kidneys, leading to organ failure.
VetBooks.ir The disease has a mortality rate of up to 70%.

Causes and predisposing factors

The main causes of hyperlipaemia are insufficient food intake and stress. Overweight female
ponies and donkeys are particularly susceptible. Other predisposing factors include:

• pregnancy and lactation (which require additional energy)
• insufficient provision of food, e.g. starvation of laminitic ponies

• any disease that reduces food intake, e.g. severe dental disease or a heavy parasite burden

• stress, e.g. change of home or management, transport, severe weather conditions, the loss

of a companion, recovery from surgery
• sedentary lifestyle and overfeeding of high carbohydrate diets to already obese animals

• old age

Pain and anxiety can be trigger factors as they cause the release of hormones (e.g. cortisol)

that increase the breakdown and release of stored body fat into the blood.

Why does the disease occur?

The liver plays an important part in maintaining the horse’s energy balance. When food is
plentiful, the plasma glucose that is not needed as an immediate energy source is converted to

glycogen and stored in the liver and skeletal muscles or converted to body fat. This process
relies on the action of the hormone insulin. At times when the energy intake is reduced or the
nutritional demands increase, glycogen stores are used up and fatty acids are released into the

blood from fat sources as an alternative form of energy. This is a normal physiological
response.

The release of fatty acids is normally inhibited by insulin and glucose but many obese
ponies and donkeys with large internal deposits of fat are insulin resistant (see Chapter 20)

and this causes severe disruption to the normal energy metabolism. The combination of
insulin resistance and insufficient energy intake or stress leads to overproduction of

triglycerides which build up to dangerously high levels in the circulation. Fatty infiltration of
the liver and kidneys can lead to liver or kidney failure. This disease can progress rapidly. If

any fat pony or donkey goes off its food, it is one of the first things to consider.