Management of Chronic Grass Sickness Patients

Dr E Milne, BVM&S, PhD, DipECVCP, FRCVS, Veterinary Pathology Unit, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, Roslin, Midlothian, EH25 9RG

INTRODUCTION

Grass sickness (equine dysautonomia) is a disease of horses, ponies and donkeys which is manifest by impaired activity of the gut due to damage to the autonomic (involuntary) nervous system. The cause is not proven but recent evidence strongly implicates involvement of the bacterium, Clostridium botulinum. The disease occurs mainly in grazing horses aged 2 to 7 years during the spring and summer with a peak incidence in May. More cases are seen in the east of Scotland but the disease occurs in most parts of the UK mainland. Grass sickness occurs in three overlapping forms, acute, subacute and chronic. In the acute disease, the signs come on suddenly and are severe. These signs include colic, reflux of green stomach fluid down the nose, difficulty in swallowing, muscle tremors, abnormal sweating patterns, impaired gut activity and impaction of the colon. Such cases cannot be treated and euthanasia is the only option. If they are not put down, acute cases will die an unpleasant death within 2 days of the onset of symptoms. In subacute cases, the signs are milder than in the acute cases. Most require euthanasia if they are unable to swallow but some progress to the chronic form. In chronic grass sickness cases, defined as cases which are still alive 8 or more days from the onset, the signs start more slowly and include marked weight loss, variable difficulty in swallowing and abdominal discomfort, muscle tremors, sweating, slow gut activity and a “snuffling” sound during breathing, due to blockage of the nasal passages with mucus. Success can be achieved in treating this form of the disease in some cases.

CASE SELECTION

Before treatment of chronic cases is contemplated, it is very important that their suitability for treatment is properly assessed. Cases which are unlikely to survive tend to have more severe difficulty in swallowing, a poorer appetite, more colic episodes, quieter gut sounds and more severe nasal crusting than those which survive although for any individual case, the outcome can be difficult to predict. In general, cases which have marked difficulty in swallowing, show frequent or severe colic episodes, have a discharge of pus from the nose or have become so emaciated that they have difficulty getting up are unlikely to survive. The horse’s attitude is also important; those which have “given up” and are not prepared to eat or show an interest in their surroundings are unlikely to respond. Age is not important and a 17 year old is as likely to survive as a two year old.

Even if the horse fulfils the above criteria, the owner should realise that management of a chronic case at home is extremely onerous, time-consuming and emotionally taxing. If treatment is to be undertaken, it must be carried out fully for any chance of success: anything less than 100% effort will result in failure. Unfortunately, even with 100% effort, the outcome can still sometimes be unsuccessful and owners should be aware of this.

FEEDING AND FLUID REQUIREMENTS

Having decided that a case is suitable for treatment, the feeding should be considered next. Ideally, a high energy, high protein diet which is easily swallowed should be fed e.g. a high energy cereal meal (such as Baileys No 1®, Baileys Horse Feeds Ltd) plus a good quality coarse mix. Alfalfa fibre is a good roughage to use as it is also high in protein (e.g. Alfa A®, Dengie Crops Ltd). Succulents are also suitable but must not form the sole diet e.g. good grass (cut and brought to them at first) or shredded carrots or turnip. However, the patients will eat a wide variety of other feeds including hay, horse nuts, alfalfa nuts, bruised oats, rolled or boiled barley, soaked sugar beet pulp, bran, apples, cabbage, milk pellets and beer and it is more important that they have what they want even if it does not seem like the ideal diet. In our experience, the preferred feeds are coarse mix, oats mixed with warm, diluted molasses, cut grass, carrots and apples. Some horses prefer their food soaked and others prefer it dry. If the feed is to be dampened, diluted molasses can be used but too much molasses can cause diarrhoea. The energy content of the diet can be increased by adding up to 500ml of corn oil to the daily ration. Any animal with a tendency to choke should probably not be given hay or sugar beet pulp. Small amounts of fresh feed should be offered at least 4-5 times daily.

Appetite often varies very markedly from day to day, both in quantity and food preference and “good” days are often followed by “bad” days. Few horses selected for treatment will eat well and for more than four consecutive days in the early stages of treatment. Initially, it is best to keep them stabled in a deep straw-bedded box but short walks in hand 2-3 times daily are important for stimulating gut motility and to keep their interest. As they improve, they can be put out to good pasture, starting with 20-30 mins and gradually increasing. Fresh water should always be available. In the author’s experience, intravenous fluid therapy and feeding by stomach tube will not be required in most cases which have a chance of survival and so will not be discussed here.

DRUGS USED IN TREATMENT

Painkillers Some cases will show mild to moderate abdominal discomfort, often soon after eating. These colic episodes usually wear off in a short time but if not, or if in any doubt, veterinary advice should be sought.

Appetite stimulants In some cases which have a poor appetite despite being able to swallow, appetite stimulants can sometimes be useful e.g. Valium®. Your vet should be consulted about this.

Lubricants Lubricants in the form of liquid paraffin can be given by your vet via a stomach tube in the early stages, if required, but this is rarely necessary. Purgatives must be avoided.

Probiotics Probiotics are live microbial feed supplements which are designed to improve the intestinal microbial flora. Trials have not been conducted on their value in chronic grass sickness, but slow gut motility and a poor or abnormal appetite is likely to adversely affect the normal bacterial and protozoal flora and therefore digestion. A variety of commercially available probiotics containing live bacteria and yeasts can be used although the extent to which they are beneficial is unknown.

OTHER ASPECTS OF MANAGEMENT

Many horses with chronic grass sickness have a reduced body temperature, sometimes as low as 35.5°C and are best rugged with a warm rug which will also allow sweat to evaporate (e.g. Thermatex®, Thermatex Ltd., Cardigan). Surprisingly, rugging will often prevent sweating so that the horse is found to be dry under the rug and wet where uncovered.

The importance of human contact in keeping the horse interested and stimulated cannot be overemphasised and the horse should be visited frequently. Keeping the patient clean is obviously important and they should be groomed at least twice daily to prevent the coat becoming scurfy and sticky. Washing of sweaty areas may sometimes be required but washing the whole animal is best avoided. Many cases show nasal crusting which makes nasal breathing difficult and discourages them from eating because they cannot smell their food. The accessible part of the nostril should be cleaned in warm water several times daily and carefully dried afterwards. If necessary, petroleum jelly can be put just inside the nostrils to prevent excoriation from the discharges. Encouraging removal of the secretions higher up the nasal cavity can be difficult. Exercise encourages the horse to sneeze out the material and steaming with a decongestant such as Vick® in a bucket held under the nose can help, but ensure that the solution is not too hot.

PROGRESS AND OUTCOME

There are several complications which may arise during treatment. The major problems are diarrhoea, choke and inhalation pneumonia. Diarrhoea occurs at some stage in approximately 30% of treated cases and usually resolves by itself. If it persists, the outlook is poor. Choke occurs occasionally and generally resolves spontaneously. However, veterinary advice should be sought if it occurs, the diet should be examined and more easily swallowed material should be fed. Inhalation pneumonia from inhaled food or nasal secretions is the most serious complication. Sudden onset of laboured breathing, a foul-smelling breath and discharge of pus, which is often greenish, from the nose suggests this complication. Immediate antibiotic therapy will be required in such cases but the outcome is sometimes fatal.

If no complications arise, the horse should gradually start to gain weight at approximately 3-5 weeks from the onset. A delay of a week of two between improved appetite and weight gain should be expected. Return to full weight can take months and a few cases never regain their original weight. Abnormal sweating and difficulty swallowing should also gradually improve over a period of months. If the horse is doing well 6-8 weeks from the onset, the chances of survival are good and relapses rare. With very careful attention to the details described above, the recovery rate in chronic cases selected for treatment is approximately 50%. It is often said that grass sickness cases never fully recover and are subsequently useless for work. A few survivors continue to sweat and show fatigue at exercise but the vast majority of recovered cases have, in our experience, returned to work including hacking, riding school work, hunting, eventing, racing and breeding.

26/5/04 MANAGEMENT OF CHRONIC GRASS SICKNESS PATIENTS Dr E Milne BVM&S, PhD, DipECVCP, FRCVS Produced by the Equine Grass Sickness Fund