Equine Grass Sickness

Equine grass sickness (EGS) is a frequently fatal disease of horses with a mortality rate in excess of 90%.  The condition affects the nervous system that controls involuntary functions, the so-called ‘autonomic nervous system’ and hence an alternative name for the disease ‘equine dysautonomia’.  The gastro-intestinal tract (GIT) is particularly affected although some of the signs of the disease are related to nerve damage distant from the GIT.

EGS is classified into 3 broad types, based on the length of survival from the onset of clinical signs:

• Acute Grass Sickness (AGS) cases survive 1-2 days
• Subacute Grass Sickness (SAGS) cases survive 2-7 days
• Chronic Grass Sickness (CGS) cases survive more than 7 days 

The most severely affected body system is the GIT producing clinical signs of intestinal paralysis of varying degree or colic although other signs are also often seen

The horse in this picture is a CGS case showing emaciation due to rapid and severe weight loss.  Emaciation such as this can occur over a period of 7 days and is an indicator of the chronic form of EGS.