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Introduction to Metabolic Disorders of Horses

ByAndrew J. Allen, DVM, PhD, DACVIM-LAIM
Reviewed/Revised Oct 2019

Metabolism refers to all processes in the body that break down and convert ingested substances into the energy and nutrients needed to sustain life. Foods, liquids, and drugs all undergo metabolic processes within the body. Many foods are complex materials that need to be broken down into simpler substances, which in turn become “building blocks” for the body to use as needed. For example, protein is broken down into amino acids, which are used to build new proteins and regulate key metabolic reactions. Enzymes, are proteins that stimulate biochemical reactions for many metabolic processes. Whenever the function of an enzyme is altered, a metabolic disorder can develop. Metabolic disorders are important because they can affect energy production or damage tissues critical for survival. They may be inherited or acquired. Acquired metabolic disorders are more common and significant. Metabolic disorders may result in a substance rising to toxic levels (a storage disorder), or a necessary substance may not be produced, causing a deficiency.

Metabolic Storage Disorders

Metabolic storage disorders are characterized by the accumulation of a substance within cells due to the body’s inability to break it down (metabolize it) because of a partial or complete lack of a certain enzyme. The missing enzyme may result in a substance building up to a toxic level. Although storage diseases are often widespread throughout the body, most signs are due to the effects on the central nervous system. Metabolic storage disorders can be either genetic or acquired.

Genetic (inherited) storage diseases are named according to the specific metabolic byproduct that builds up in the body. These diseases are progressive and usually fatal because specific treatments do not exist. Polysaccharide storage myopathy is one example of an inherited storage disease in horses, which results in sore muscles (‘tying up’).

Acquired storage diseases can be caused by eating plants that contain inhibitors of specific enzymes. Eating locoweed plants (Astragalus or Oxytropis species) for a long time can result in an acquired neurologic storage disease. Several toxic components of these plants interfere with the activity of a specific enzyme. Horses are highly susceptible to locoweed intoxication.

Locoweed

For More Information

Also see professional content regarding metabolic disorders.

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