Motor events in equine large colon.

The research focuses on the functioning and characteristics of the equine large colon, particularly the area where the ventral and dorsal divisions meet. This area is seen to resist the flow moving away from the mouth, possibly due to a pacemaker present. The study also observes a rise in pressure within the colon during feeding.

Characteristics and Significance of the Equine Large Colon

• The large colon in horses is primarily responsible for the fermentation of cellulose. Cellulose is a complex carbohydrate found in the plant cell wall which is a major part of horses’ diet, known for its high fiber content.
• The study investigates two specific parts of the colon: the ventral (lower) and dorsal (upper) divisions, especially their junction, which is found to resist the flow of contents moving from the horse’s mouth towards its rear (aboral flow).

Presence of a Pacemaker

• In the context of the digestive system, a pacemaker is a region that regulates the contractions and relaxations of muscles in the organ (a process known as peristalsis), thus controlling the flow of food and later waste materials.
• Such a pacemaker is presumably present in the junction of the ventral and dorsal divisions of the horse’s large colon. This research suggests that the pacemaker is what causes the aforementioned area to resist aboral flow, and facilitates the colon’s reservoir function, effectively storing the processed food products.

Effects of Feeding and Extrinsic Nerve Stimulation

• Upon feeding, the researchers observed a general rise in the recorded pressure peaks inside the colon, especially in the first hour.
• The increase in pressure during feeding was not stopped or interrupted even after resection (surgical removal or cutting) of the extrinsic nerve supply. The extrinsic nerves are those that come from outside an organ, providing it with inputs from the brain and spinal cord.
• Electrical stimulation of these extrinsic nerves sometimes mimicked the increase in intraluminal (inside the colon) pressure, similar to what happens when feeding begins. This indicates the possibility of these nerves having a role in the modulation of colon function around feeding times.