A vet's view

Grass sickness is harrowing for both horse and owner, including for vets. Liz Richardson MRCVS details her experience when her own horse was afflicted

- Liz Richardson

EQUINE GRASS SICKNESS (EGS) is a disease of grazing horses, ponies and donkeys in which there is damage to parts of the nervous system that control involuntary functions. There are three forms of EGS: acute, subacute and chronic, although clinical cases do not always fall exclusively into one category. The acute and subacute forms are invariably fatal, but with intense and ongoing treatment, chronic cases can survive.

Multiple risk factors have been identified, including the age of the horse, the time of year and geographical location, but unfortunately, the cause is still unclear.

The clinical signs of EGS reflect the extent of damage to the nervous system. The major signs relate to partial or complete paralysis of the digestive tract from the oesophagus onwards. In acute EGS, the signs are severe and appear suddenly. They are:

A high heart rate - often above 60 beats per minute (bpm); compared with a normal range of 28 to 44.

Gut paralysis, leading to severe colic and difficulty in swallowing.

Constipation. If any dung is passed, the pellets are small and hard, and may show a white coating of dried mucus.

Dehydration. Fine muscle tremors and patchy sweating may occur.

The stomach may become very bloated with foul-smelling fluid, which can pour down the nose.

With subacute EGS, the signs are similar but are less severe. Small amounts of food may still be consumed.