The microbial niche created by the equine cecum is part of a complex and delicate ecosystem. The cecum is commonly referred to as the fermentation vat of the equine digestive system. The fermentation is carried out by microbes that inhabit this environment; mainly by bacteria, but also by some protozoans and some vegetative growth of phycomycete fungi. (Mackie, 1997) These microbes are a vital part of the digestive system of horses, with the cecum accounting for approximately 15% of the digestive tract. (Wright) The environmental conditions of the cecum directly effect the type of microbes that can survive there. The cecum is located between the stomach and the colon and is classified as part of the large intestine. The pH of the cecum is relatively neutral; the stomach acidic and the colon alkaline. pH fluctuations in either direction can result in changes in the populations of microbes in the cecum. (Harman) The cecum is four feet long and has a capacity of about 26 to 32 liters. Both the entrance from the stomach and the exit to the colon are located at the top and rest of the cecum extends down from there. This pocket like structure ties in with the relatively long time, approximately 7 hours, that contents take to pass through the cecum and the relatively low motility in this part of the GI tract, which helps microbes stay in place.