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Monday, 25 June 2018

Grass Sickness: The Most Dangerous Equine Illness


Grass sickness is a illness that causes the main gut to become paralysed.  There has been a lot of speculation over what causes grass sickness although it is contracted by grazing and in some cases eating hay.

It is thought that pastures with high nitrogen or soil disturbances is higher risk.  There are trial vaccines being done at the moment that are being used to see if the bacteria Clostridium botulinum is what causes grass sickness.  

There are also higher chances of getting grass sickness when the horse is stressed, new to the yard or a good to fat body weight.  It is most likely to happen when the weather has been dry and 7-11°C.  

Horses that are 2-7 years old are more likely to get grass sickness although horses of all ages can get it.  It has also been found that horses that are given certain types of wormers are more at risk.   
It has been thought that a mineral deficiency can cause more of a risk.  Although this is unlikely it is thought that a horse with selenium deficiency which means there is a reduced number of protective antioxidants in the body.  

As mentioned above, the newest theory is that the bacteria clostridium botulinum (a soil based bacteria) could be the cause.  This is why horses are having a trial vaccine to see if that helps.  

Peak times for grass sickness is spring and summer with a higher number of cases in May.  There is then another peak in September when the weather gets slightly colder but is still dry.  


Acute                                                 Subacute                             Chronic 

Depression                                         Tucked up Abdomen                   Severe Weight Loss

No gut sounds                                    Weight Loss                                Tucked up Abdomen

Distended Abdomen                       Difficultly Swallowing                Base Narrow Stance

Salvation                                            High Heart Rate                          Dry & Inflamed Nasal Passage

Gastric Reflux                                    Colic                                           Droopy Eyes

Muscle Tremors                                 Gastric Reflux                            Slightly High Heart Rate

Droopy eyes                                       Patchy Sweating                         Muscle Tremors

Patchy sweating                                 Droopy Eyes                               Mild Colic

Difficultly Swallowing                      Colon Impaction                         Patchy Sweating

Small intestine distention                  Muscle Tremors                          Reduced Gut Mobility

Colic                                                     Reduced Gut Mobility

Colon impaction                                Dry & Inflamed Nasal Passages

High Heart Rate


Treatment for grass sickness is often not a choice.  It goes into the three categories of the illness.


Horses that get Acute grass sickness usually either pass away or need to be PTS within two days.  It is best not to try treatment.


Horses who have subacute grass sickness usually pass away or need to be PTS within one week.  It is best not to try treatment. 


Horses who have chronic grass sickness may be able to give treatment a go if they aren't in much pain and are still eating even a small amount.  The horse will have to be nursed 24 hours a day and it may not help the horse.  Feeding them easy to eat, high energy food is important.  Feed concentrates soaked with molasses, fruit and veg or really anything your horse will eat.  They must be groomed often, rugged to avoid sweating and hypothermia and kept an eye on at all times.

It is important to remember that not all chronic cases can be treated if the horse is in a lot of pain or has stopped eating.


This is hard to tell as we don't known the cause of grass sickness.  There are some ways to help your horse to avoid getting grass sickness.

Lowering the risk

  • Stabling during peak times of grass sickness 
  • Co-grass with sheep or cows 
  • Giving hay in the field or part stabling 
  • No mechanical poo picking 
  • avoid soil disturbance
  • Stabling horses when the weather is dry and 7-11°C for more than a week 

More of a risk 

  • Co-grazing with fowl
  • Full turn out 
  • Soil disturbing 
  • Feeding changes 
  • Ivermectin worming 
  • Stressed horses 
89% of cases are horses who are turned out full time, 9% of cases are part stabled horses and 2% are of stabled horses.  

Horses who are more likely at risk are between the ages of 2-7 years old, good to fat condition, are new to the yard or stressed and horses who are turned out full time.  


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