a.k.a. Large Intestine the hind gut comprises the blind ending pouch of the caecum, the large colon, small colon, rectum, and anus. The total length is approximately seven meters, and it has a capacity of up to 150 liters in a 450kg adult horse. It is the site of fibre digestion which is achieved by means of microbial fermentation. It is also where most of the water is absorbed from the ingesta, and hind gut water can act as a reservoir from which the horse can draw as needed. The hind gut microbiota is critical to digestive health and efficiency and exerts influence on overall immunity as well as the nervous system and behavior via the gut-brain axis.
See also Gut, Dysbiosis, Microbiome