section_path: Characteristics/Digestive system
section_name: Digestive system
paragraph_text: Digestive system
  
  Cattle are ruminants, meaning their digestive system is highly specialized for processing plant material such as grass rich in cellulose, a tough carbohydrate polymer which many animals cannot digest. They do this in symbiosis with micro-organisms – bacteria, fungi, and protozoa – that possess cellulases, enzymes that split cellulose into its constituent sugars. Among the many bacteria that contribute are Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus. Cellulolytic fungi include several species of Neocallimastix, while the protozoa include the ciliates Eudiplodinium maggie and Ostracodinium album. If the animal's feed changes over time, the composition of this microbiome changes in response.
  
  Cattle have one large stomach with four compartments; the rumen, reticulum, omasum, and abomasum. The rumen is the largest compartment and it harbours the most important parts of the microbiome. The reticulum, the smallest compartment, is known as the "honeycomb". The omasum's main function is to absorb water and nutrients from the digestible feed. The abomasum has a similar function to the human stomach.
  
  Cattle regurgitate and re-chew their food in the process of chewing the cud, like most ruminants. While feeding, cows swallow their food without chewing; it goes into the rumen for storage. Later, the food is regurgitated to the mouth, a mouthful at a time, where the cud is chewed by the molars, grinding down the coarse vegetation to small particles. The cud is then swallowed again and further digested by the micro-organisms in the cow's stomach.