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The large intestine is the termination point of the gastrointestinal tract and includes several components that are essential to horse anatomy.
The significant distinction in equine anatomy is that horses uniquely referred to the ascending colon as the large colon and the descending colon as the small colon.
- In contrast to other species where the terminology used is:
- Ascending colon
- Transverse colon
- Descending colon
The transverse colon in horses is relatively short and narrows to join the descending colon, which is termed the small colon.
The function of these components is to facilitate digestion and the slow passage of food.

The cecum in horses is notably smaller compared to other species, yet it plays a key role in digestion.
The ileum opens into the cecum through the ileocecal valve, which prevents backflow into the ileum.
Additionally, there is another valve where the cecum connects with the ventral colon, preventing reverse flow of material.
The physiology of the large intestine is crucial; it incorporates fermentation processes which are especially pronounced in horses due to their unique digestive adaptations.

Horses are classified as hindgut fermenters, meaning that their fermentation occurs after the small intestine.
There are two types of carbohydrates identified:
- Hydrolyzable carbohydrates (digestible in the small intestine)
- Non-hydrolyzable carbohydrates (fermented in the large intestine)
- Only microbial activity can digest non-hydrolyzable carbohydrates in horses.
The large intestine of horses is responsible for:
- Fermentation
- Absorption of water
- Absorption of some amino acids and proteins.
In contrast, in other animals, absorption predominantly occurs in the small intestine.
If horses consume excessive amounts of starch, it can lead to obstruction since not all can be digested in the limited capacity of the small intestine.

During fermentation, three main volatile fatty acids are produced, which are essential for energy:
- Acetate
- Propionate (precursor for gluconeogenesis)
- Butyrate
Acetate primarily aids in energy production in the liver while butyrate serves for energy production and cellular homeostasis especially within the intestinal cells.
There is a particular emphasis on maintaining a neutral pH in the gastrointestinal tract to support microbe activity as well as to prevent acidosis.
- Excessive volatile fatty acids lead to lower pH and possible acidosis, which pose health risks.

Horses are prone to colic, a clinical symptom rather than a specific disease.
The overarching anatomy and physiology of the equine digestive system, especially the large intestine, create vulnerabilities to colic.
Colon adaptations, particularly in the formation of lateral flexures, contribute to the horse's susceptibility to colic.
It is essential to understand how the equine digestive process differs from those of other animals.

Water absorption occurs significantly in the large intestine.
This mechanism is critical to maintaining proper osmotic pressure and pH balance necessary for microbial fermentation.
Bicarbonate secretion and the exchange of ions (e.g., hydrogen ions and sodium ions) are vital to sustain a favorable pH in the large intestine, thus supporting fermentation.

The motility of the equine large intestine is relatively slow, reflecting the need for fermentation processes to occur efficiently.
The primary contractions in this region are mass contractions occurring every three to five minutes, critical for the transport of materials through the cecum to the colon.
These contractions are complemented by peristaltic movements that are functionally adapted to horses.

Understanding anatomy plays a vital role in diagnosing disorders such as colic through techniques like rectal palpation.
The transitions of digestive structures can be palpated to ascertain their health.
The nephrosplenic ligament, connecting the spleen to the kidney, can influence the positioning of intestines, leading to colic due to displacements.
Early diagnosis through critical observations during rectal examinations can lead to timely intervention and potential life-saving actions.

The equine digestive system, particularly the large intestine, is adapted for efficient fermentation, leading to unique challenges in their dietary management.
Knowledge of the specific anatomy and physiology is paramount for those involved in equine health, disease prevention, and management strategies in veterinary practice.
Emphasizing balanced nutrition to avoid issues related to excessive hydrolyzable carbohydrates forms an essential role in equine dietary formulations.