Digestion Begins at the Tip of the Nose
The equine digestive system is one of the most complex subjects in horse feeding. Most horse owners probably don’t realize that the lips and teeth, which are responsible for food intake, already belong to the digestive tract. The duration and intensity of chewing work, for instance, depend on the fiber content of the feed. That’s why concentrated feed is eaten much faster than roughage like hay. While chewing, horses produce saliva, which mixes with the food. A horse can produce up to 5 kg of saliva per 100 kg of body weight per day! [1]
Horses Cannot Vomit
The chewed and saliva-mixed food travels down the esophagus into the horse’s stomach. Unlike humans, horses cannot vomit due to a strong muscle at the stomach entrance, which prevents the food from flowing back into the esophagus. As a result, overloading the stomach can be extremely dangerous for horses. Their stomach, with a volume of around 15-20 liters, is relatively small in proportion to their body size. [2] This is one reason why frequent, smaller meals are recommended for horses. A maximum of 0.3 kg of concentrated feed per 100 kg of body weight per meal is suggested. [3]
Horse Stomach Structure
Horses have a single-chambered, composite stomach, meaning it consists of two parts: the glandular (acid-producing) and the non-glandular (acid-free) sections. This separation can be clearly observed during a gastroscopy (endoscopy) as the two sections are visibly divided by a line known as the "Margo plicatus" [4]. The upper, non-glandular part of the stomach is white in color, while the lower glandular part is reddish.
What About Stomach Ulcers?
Stomach ulcers are often found at the junction between the two stomach parts. This is because the non-glandular part of the stomach is not designed to be exposed to stomach acid. As horses are continuous eaters, they constantly produce stomach acid, whether they are eating or not. If there are long breaks between meals (>4 hours), an excess of acid can build up and damage the sensitive non-glandular mucosa. This can be a very painful issue for horses. Stress, excessive amounts of concentrated feed, or pain can also lead to stomach ulcers. Symptoms of stomach inflammation or ulcers are highly varied and sometimes not recognized. To prevent this, it’s recommended to always provide enough roughage, such as hay (at least 1.5 kg of hay per 100 kg of body weight). Additionally, feeding breaks should not exceed 4 hours. In sensitive horses, a stomach protector can be fed to help, as mucus-producing ingredients coat the stomach lining and protect it from the aggressive acid. However, it is important to investigate the causes of stomach ulcers and eliminate any triggers if possible.
Horses Have No Gallbladder
From the stomach, the partially digested food moves into the intestines, which can reach up to 40 meters in length, depending on the size of the horse. The small intestine, around 25 meters long, is where the digestion of starch, fats, and proteins takes place. A notable feature of horses is that they don’t have a gallbladder. Instead, bile acids are continuously produced by the liver, which neutralizes stomach acid and aids in fat digestion.
The Role of the Cecum
The horse's large intestine consists of the cecum, large colon, small colon, and rectum. The cecum is very large, around one meter long, and plays an essential role in digestion. Without the cecum, a horse could not survive, unlike humans. The cecum and large colon serve as fermentation chambers in the digestive tract. The large intestine is primarily responsible for digesting fiber. Additionally, B vitamins, Vitamin C, and Vitamin K are produced and absorbed by the bacteria in the cecum. The horse’s body does not depend on external sources for these vitamins unless there is an imbalance in the gut bacteria, which can occur due to antibiotics or certain medications. Stress or spoiled feed can also lead to dysbiosis (an imbalance in gut flora).
Supporting Gut Flora
If there is suspicion of an imbalance in the gut flora, supplementing B-vitamins can be useful. Feeding live yeast (Saccharomyces cerevisiae) can also help support the microorganisms in the large intestine and restore balance.
Dysbiosis and Fecal Consistency
The large intestine also plays a role in the reabsorption of water. An imbalance in the gut can affect the water absorption process, leading to diarrhea or soft stools. For these conditions, it is important to monitor the gut flora. Products with water-binding properties, such as pectin, kaolin, or psyllium husk, can help improve stool consistency. Pectin, in particular, also has positive effects on the stomach lining.
Sources:
[1] Meyer, H. & Coenen, M. (2014) Pferdefütterung (5th edition), Enke Verlag, Stuttgart
[2] Meyer, H. & Coenen, M. (2014) Pferdefütterung (5th edition), Enke Verlag, Stuttgart
[3] FN (2017) Basic knowledge of horse management, feeding, health, and breeding, Guidelines for Riding and Driving, FN Verlag
[4] Nickel, R. & Schummer A. & Seiferle E. (1999) Textbook of Anatomy of Domestic Animals, Volume 2, 8th Edition, Parey Verlag, Berlin & May, A. et al. (2012) Gastric Disorders in Horses – Diagnosis and Therapy, Pferdeheilkunde 28 (2012) 4 (July/August) 388-405
