Grass sickness
Encyclopedia
Equine Grass Sickness is a rare but predominantly fatal illness in horse
s. Grass sickness may affect all types of horse, pony
and donkey
, and has affected some well known horses including the thoroughbred stallion Dubai Millennium
.
affecting the central, peripheral and enteric nervous system
s. The majority of visible clinical signs are related to paralysis within the digestive tract although nerve damage occurs throughout the body. There are three forms of grass sickness:
Clinical signs common to all subsets include: depression, anorexia, colic (moderate with AGS/SAGS and mild with CGS), excess salivation, constipation, nasogastric fluid secretion, patchy sweating, muscle tremors and eyelid drooping.
upon diagnosis as the condition is fatal. A proportion of CGS cases can survive following periods of intensive nursing. Overall the mortality rate of equine grass sickness is considered to be over 95%.
type C is involved.
Clostridium botulinum is a soil-borne bacterium, which may be better known for producing clinical signs of botulism. Research has suggested that Clostridium botulinum may cause grass sickness when the spores of C. botulinum type C are ingested and produce their toxin locally within the intestine.
Research has identified a number of other risk factors which may increase the likelihood of a horse developing grass sickness including: soil disturbance, worming with Ivermectin based dewormers, movement to new pasture, stress, grazing on a field which has previously produced a case of grass sickness.
The Equine Grass Sickness Fund [www.grasssickness.org.uk] are a dedicated charity raising funds to tackle the disease. Their website contains useful information regarding all aspects of grass sickness including management of chronic grass sickness cases.
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s. Grass sickness may affect all types of horse, pony
Pony
A pony is a small horse . Depending on context, a pony may be a horse that is under an approximate or exact height at the withers, or a small horse with a specific conformation and temperament. There are many different breeds...
and donkey
Donkey
The donkey or ass, Equus africanus asinus, is a domesticated member of the Equidae or horse family. The wild ancestor of the donkey is the African Wild Ass, E...
, and has affected some well known horses including the thoroughbred stallion Dubai Millennium
Dubai Millennium
Dubai Millennium was a Thoroughbred racehorse and sire, bred in the United States but trained in the United Kingdom and Dubai during his racing career which ran from 1998 and 2000. He is notable for winning a series of major races in 1999 and 2000 including the Dubai World Cup...
.
Clinical signs
Grass sickness is a polyneuropathyPolyneuropathy
Polyneuropathy is a neurological disorder that occurs when many peripheral nerves throughout the body malfunction simultaneously. It may be acute and appear without warning, or chronic and develop gradually over a longer period of time. Many polyneuropathies have both motor and sensory...
affecting the central, peripheral and enteric nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
s. The majority of visible clinical signs are related to paralysis within the digestive tract although nerve damage occurs throughout the body. There are three forms of grass sickness:
- acute grass sickness (AGS) - horses display signs of colic and require euthanasia or die within 48 hours
- subacute grass sickness (SAGS) - horses display clinical signs similar to AGS but with less severity and may survive up to 7 days
- chronic grass sickness (CGS) - horses present with severe and rapid weight loss and a selected portion of these cases may survive.
Clinical signs common to all subsets include: depression, anorexia, colic (moderate with AGS/SAGS and mild with CGS), excess salivation, constipation, nasogastric fluid secretion, patchy sweating, muscle tremors and eyelid drooping.
Diagnosis
Diagnosis of grass sickness in the live animal requires a thorough clinical examination including a rectal examination. Definitive diagnosis can only be made at surgery (where biopsies of the gut are taken) or at post-mortem (where biopsies from the nerves are taken). Differential diagnoses for grass sickness are varied and include: any other cause of colic and weight loss, tying-up, laminitis, botulism, choke and dental problems.Treatment
There is no treatment for grass sickness. All cases of AGS and SAGS should be euthanisedEuthanasia
Euthanasia refers to the practice of intentionally ending a life in order to relieve pain and suffering....
upon diagnosis as the condition is fatal. A proportion of CGS cases can survive following periods of intensive nursing. Overall the mortality rate of equine grass sickness is considered to be over 95%.
Cause
The cause remains unknown, however present research suggests that toxin production from the bacterium Clostridium botulinumClostridium botulinum
Clostridium botulinum is a Gram-positive, rod-shaped bacterium that produces several toxins. The best known are its neurotoxins, subdivided in types A-G, that cause the flaccid muscular paralysis seen in botulism. It is also the main paralytic agent in botox. C. botulinum is an anaerobic...
type C is involved.
Clostridium botulinum is a soil-borne bacterium, which may be better known for producing clinical signs of botulism. Research has suggested that Clostridium botulinum may cause grass sickness when the spores of C. botulinum type C are ingested and produce their toxin locally within the intestine.
Risk factors
The main risk factor for grass sickness, as the name may suggest, is grass. The disease is almost always seen in grazing animals, although there are isolated reports of the condition occurring in stabled horses. Grass sickness is most frequently seen in young horses aged between two and seven, and is particularly prevalent during April, May and June, and later in the autumn, after a spurt of grass growth.Research has identified a number of other risk factors which may increase the likelihood of a horse developing grass sickness including: soil disturbance, worming with Ivermectin based dewormers, movement to new pasture, stress, grazing on a field which has previously produced a case of grass sickness.
Research
Current research in equine grass sickness includes development of a nationwide surveillance scheme for grass sickness in Great Britain. This scheme hopes to identify all cases of grass sickness which occur from 2000 onwards. This scheme is run by the Animal Health Trust, in collaboration with the Equine Grass Sickness Fund, the University of Edinburgh and the University of Liverpool, following funding from The Horse Trust. More information on this scheme can be found at the dedicated website [www.equinegrasssickness.co.uk]The Equine Grass Sickness Fund [www.grasssickness.org.uk] are a dedicated charity raising funds to tackle the disease. Their website contains useful information regarding all aspects of grass sickness including management of chronic grass sickness cases.
External links
- http://www.worldhorsewelfare.org/information/horse-advice-library World Horse Welfare (UK)
- Grass sickness in horses Horse & Hound magazine (UK)
- http://www.horsetalk.co.nz/news/2009/07/037.shtml Horsetalk (NZ)
- https://www.nationalponysociety.org.uk/uploads/assets//welfarefiles/WelfareGrassSicknes.pdf National Pony Society
- Equine Grass Sickness Surveillance
- http://www.aht.org.uk/egss/pdf/newsletter-winter08.pdf Newsletters
- Equine Grass Sickness Fund