Inflammatory bowel disease (IBD) is a broad term that describes a group of diseases marked by inflammation in the gastrointestinal tract of the horse.
Horses with IBD may show outward signs including recurrent colic, diarrhea, weight loss, and low energy levels.
IBD in horses is a rare, but severe, inflammatory condition that affects gut permeability and nutrient absorption.  In some types of IBD, other tissues are also affected causing a broader range of symptoms that can include skin lesions and anemia.
Although the exact cause of IBD is unknown, it is thought to involve an abnormal immune response to bacteria, parasites, or dietary components that are normally present in the gut. 
IBD is a serious condition that significantly increases the risk of colic in affected horses. Because it can dramatically affect nutrient absorption, it is often associated with weight loss even when the horse’s appetite is normal.
Genetics are likely to play a role in IBD, as Standardbreds are more likely to develop this condition. However, dietary strategies such as providing more frequent small meals of highly digestible, simple feeds may help alleviate symptoms and improve gut function in affected horses.
Consult with your veterinarian and equine nutritionists if you suspect IBD or other gut disorders in your horse. You can submit your horse’s diet for complementary evaluation by our equine nutritionists to optimize nutritional support of gut health.
What is Inflammatory Bowel Disease?
In healthy animals, immune responses occur when an unknown or potentially harmful substance enters the body, including pathogens such as bacteria and viruses.
IBD occurs in horses when there is an abnormal immune response to harmless bacteria and other substances.
In the case of IBD, white blood cells from the immune system infiltrate the intestinal lining of the small intestine which disrupts cells that absorb nutrients, secrete hormones and produce the mucous barrier. 
These horses often have severely low levels of protein in the blood because of poor absorption and enteric loss of proteins, meaning protein from the blood enters the intestine.
Symptoms of IBD in Horses
As with many immune-mediated diseases, a variety of symptoms can present in the horse, most of which are also symptoms of other diseases, making diagnosis difficult. 
Common symptoms include:
- Weight loss despite proper nutrition
- Decreased appetite despite normal oral exam
- Poor body condition
- Diarrhea (if the large intestine is affected as well)
- Abdominal swelling (edema)
- History of mild colic or concurrent episodes of coli
Many of these symptoms can present in a horse with poor gut health. This does not mean every horse with poor gut health has IBD as there can be many causes of gastrointestinal dysfunction in horses.
These symptoms always warrant a visit by your veterinarian to determine the underlying cause. You may need to make adjustments to your horse’s environment, routine or feeding program to better support immune and gut health.
Horses that struggle to maintain a healthy weight or have inconsistent stool quality would likely benefit from a forage-first feeding program that is rich in fibre. Diets that are high in grain are more likely to lead to gut dysfunction.
Horses with digestive issues may also benefit from a comprehensive gut health supplement such as Mad Barn’s Optimum Digestive Health pellets.
Optimum Digestive Health contains probiotics, prebiotics, yeast, toxin binders and digestive enzymes to support digestion, immune function and a healthy microbial balance in the gut.
Types of Inflammatory Bowel Disease
1) Eosinophilic Enterocolitis and Multisystemic Eosinophilic Epitheliotropic Disease (MEED)
Eosinophilic enterocolitis is inflammation of the intestine caused by eosinophil and lymphocyte (two types of white blood cells) intrusion into the lining of the small intestine as well as the large intestine. Horses with this condition often develop colic.
A more severe version of this condition is called multisystemic eosinophilic epitheliotrophic disease (MEED) which affects the small intestine and other organs including the liver, skin, and lungs.
Horses with MEED often have very poor skin quality and even skin lesions, which can be used to diagnose MEED via biopsy.
The cause of eosinophilic enterocolitis or MEED is thought to be an allergic response, to an inhaled, dietary or parasitic antigen. It is thought that MEED might be caused by larvae (eggs) of parasites that infect several tissues.
Eosinophilic enterocolitis and MEED appear to be most common in young Standardbred and Thoroughbred horses. However, horses of any sex, breed, or age can be affected.
2) Granulomatous Enteritis (GE)
This type of IBD is similar to Crohn’s Disease in humans and Johne’s disease in cattle. Like all forms of IBD, the exact cause is unknown, but again, it is thought to be an abnormal immune response to bacteria or dietary components.
It often affects the ileum (most distal) segment of the small intestine.
Most horses affected by GE have chronic weight loss, poor appetite and anemia (low red blood cell count).
Granulomatous enteritis is caused by lymphocyte and macrophage intrusion of the intestinal lining of the small intestine.
This disease causes microvilli in the intestine to shrink which reduces the total surface area available for absorption of nutrients. These horses often have malabsorption, including poor absorption of simple sugars like glucose which leads to significant weig