The large pouch between the small and large intestines is called what?

The large pouch located between the small and large intestines is known as the cecum. This structure is a critical part of the digestive system in horses and other mammals, acting as a junction point where the contents from the small intestine enter before moving into the large intestine. The cecum plays a vital role in the fermentation and breakdown of fibrous materials, which is essential for the horse's ability to extract nutrients from its herbivorous diet.

In horses, the cecum is particularly large, accommodating the fermentation process necessary for digesting cellulose from plant materials. This function is key to the horse’s overall digestive health, making the cecum an important anatomical feature in equine physiology.

The other options refer to different parts of the gastrointestinal tract that do not fit the description given. The duodenum is the first section of the small intestine. The rectum is the final section of the large intestine, and the colon is a major part of the large intestine following the cecum. Each plays its own role in the digestive process, but only the cecum serves as the specific pouch mentioned in the question.