Recognition and medical treatment of gastric ulcers in horses has been well established for many years now.
Initially veterinarians thought ulcers in the digestive tract of the horse were limited to the stomach or gastric mucosa. This was a logical conclusion since the presence of the open ulcers in the stomach could be diagnosed and observed through the use of a three-metre endoscope.
However, it is becoming increasingly evident that the remaining 90 per cent of the lengthy digestive tract of the horse, especially the hind gut, is equally at risk for ulceration and various pathologies. Unfortunately problems of the digestive tract beyond the stomach, particularly those associated with the hind gut are not so easy to diagnosis, are generally overlooked and to a great extent misunderstood.
Nonetheless, these disturbances are quite common and can have a considerable impact on the overall health of the horse, negatively affecting the horse’s quality of life, disposition and performance.
In order to truly understand the unique digestive strategy of the horse, one must understand the significance of the hind gut. The cecum, and the large and small colons of the horse are collectively known as the hind gut. These structures serve as a large fermentation vat for the digestion of a high-fibre diet. Together they represent about 65 per cent of the horse’s entire digestive tract. In this 25- to 30-gallon space, populations of microbes numbering in the billions contentedly digest plant fibre into metabolic energy for the horse — working in exchange for a warm, comfortable living space.
The horse’s digestive tract is designed to effectively move plant material to the hind gut where bacteria, protozoa, yeast and other healthy microbes — the microbiome — produce enzymes which break down fibrous matter into volatile fatty acids (VFAs). Horses on total forage diets receive between 70 to 80 per cent of their metabolic energy from VFAs and owe the majority of their life-sustaining energy to billions of friendly micro-organisms housed in a co-operative benevolent relationship. A functional cecum also produces significant amounts of B vitamin complexes which are vital to many functions within the body. Most notable is their support for the nervous system, which results in their calming influence on the horse.
The horse’s digestive system has evolved to efficiently process large amounts of high-fibre forage — rather than today’s much richer diets high in sugars, simple carbohydrates and fats. These food sources are unnatural to the horse’s diet, yet are common to today’s feeding practices. When excessive grains, rich concentrates or processed feeds are fed to the horse, they inadvertently reach the hind gut where they undergo fermentation and thus interfere with the microbiome that works to ferment fibre.
These food sources fuel the growth of “unfriendly bacteria” resulting in the production of lactic acid. The lactic acid cocktail creates an unnaturally acidic environment in the hind gut by lowering the pH. The unfavourable environment results in beneficial fibre-digesting bacteria dying off and releasing toxins, called endotoxins. The imbalanced microbiome no longer fully nourishes the horse with its life-sustaining energy source. The acidic environment further weakens and compromises the protective mucous barrier and mucosa of the gut, making the gut lining abnormally permeable.
Various labels have been used to describe such imbalances: hind gut acidosis, dysbiosis (abnormal populations of gut microbes or abnormal balances of microbes), leaky gut syndrome, hind gut ulceration and colitis. All terms are likely applicable to some degree and represent a continuum of increasing disruptions to the ecosystem of the horse’s hind gut.
One of the challenges with diagnosing lower GI problems in horses is the variability and vagueness of the symptoms. Horses with digestive distress often fall into the category of “ADR” horses or horses that just “ain’t doing right.”
Symptoms such as poor appetite, picky eating habits, anxiety at feeding, poor physical condition, dullness in the eye, poor hair coat, weight loss, low-grade non-specific colic, teeth grinding, mental dullness, a change in attitude such as sourness or irritability, poor performance and reluctance to work, may indicate the presence of GI distress. It is not uncommon for these horses to be labelled with behaviour problems.
Unfortunately many elude proper attention and care since their symptoms are so varied and non-specific. Horses that experience hind gut distress share symptoms of discomfort in common with horses suffering from gastric ulcers and often many horses are experiencing both.
Symptoms which are more likely to indicate unbalanced hind gut involvement include diarrhea (intermittent or regular), sensitivity in the girth and flank areas, often described as “cinchy,” a “tucked-up” abdomen or “herring gutted,” wasting of the top line, fidgety under saddle, reluctance to move fluidly and stride evenly, abnormal postures, and dragging of toes. Many of these latter symptoms reflect an effort to protect the ailing hind gut area.
Many factors in a horse’s environment can alter GI health. Feeding practices, and external stressors such as travel, change of herdmates, training schedules, stall confinement, severe or inconsistent and inadequate exercise, medications, dewormers, vaccines and non-steroidal anti-inflammatories such as Banamine and phenylbutazone all alter the delicate, and at times precarious, microbial balance within the hind gut.
A horse’s hind gut health and its ability to effectively ferment fibre plays a significant role in keeping the horse sound. Often GI distress results in alterations to the horse as a whole whether it be attitude, health, or performance.
Nutrition and feeding protocols are by far the largest contributors to GI problems in horses. Therefore it is through dietary corrections that the most effective solutions for prevention, managing, and healing GI problems lies.
Removing, reducing or managing the contributing factors is a start in addressing the hind gut issue. Most importantly, ensure that the horse has continual access to high-quality long-stem forage, water and minimal carbohydrates.
Although supplemental prebiotics and probiotics are marketed as a resolve to gut distress in horses, their claims are only partially true for they only have limited success if the contributing factors are not addressed.
Having an awareness of the implications hind gut health has to the horse often sheds a new perspective on the health and soundness of the entire horse.