GI Morphology

1 The cow's digestive system starts with the oral cavity, including teeth and saliva Which are used to grind the food and give it enough moisture to make it easier to swallow.

Cows may chew hay at first before swallowing, but that's more to grind it up and to soak it into their saliva before swallowing it whole.

The "bolus" of food, when swallowed, moves past the pharynx and passes through the esophagus into the first chamber of the fore-stomach.

2 Cattle have one stomach with four compartments--however, cattle (and other ruminants) have three forestomachs in addition to the true stomach, known as the abomasum.

These compartments are the rumen, reticulum, and omasum, with the rumen being the largest compartment.

Cattle are ruminants, meaning that they have a digestive system that allows them to make use of otherwise indigestible foods as a main food source by repeatedly regurgitating and re-chewing them as "cud".

The cud is then re-swallowed and further digested by specialized microorganisms in the rumen.

It is the microflora that feeds the cow.

3 The rumen is where billions of bacteria, millions of protozoa and millions of fungi live to live on and break down the plant matter that the cow has swallowed, this is where fermentation occurs.

This is where the process of digestion and break-down begins after the forage is swallowed whole.

Fermentation is achieved by the microbial activity in the rumen, which enables the "decomposition" of cellulose, fibre, hemi-cellulose, and carbohydrates into volatile fatty acids, protein and energy for the cow to live on.

Microbes synthesize amino acids from non-protein nitrogen sources like urea, ammonia and butyric acid. Carbohydrates released from the softened plant tissue provide energy.

Partly digested food is regurgitated and rechewed, the molars grinding the plant matter down further and the saliva adds to the moisture content of the cud. After chewing their cud they will reswallow it for the microflora in the rumen to further digest.

4 Cattle sometimes consume foreign objects which are deposited in the reticulum. The metal, if it doesn't penetrate the reticulo-rumen wall, will stay in the reticulum and break down from the cow's gastric juices.

As the rumen contracts and mixes digesta, these foreign objects are moved, by smooth muscle contractions of the reticulo-rumen, into the reticulum. If a cow gets ill from these foreign objects puncturing the stomach lining, often a magnet is given orally to the cow to collect all these metal objects and keep them in one place.

The omasum's main function is to absorb water and some nutrients from the digesta, The omasum is the last forestomach before the chyme enters the true stomach.

The abomasum functions like the human stomach; this is why it is known as the "true stomach". It secretes protein and starch digesting enzymes to further digest the materials that weren't broken down in the rumen.

5 From the abomasum, the digesta passes into the small intestine, which is divided into three segments: the duodenum, where digestive enzymes from the liver and the pancreas are mixed in; the jejunum, which is the longest part and is where nutrients from the food are primarily absorbed; and the ileum, where the last of the nutrients are reabsorbed and part of the water from the food is reabsorbed as well.

The food then passes into the cecum and the colon; the cecum while the colon will eventually move the feces out the rectum. Once the feces have passed through the colon they are collected in the rectum until the cow has a bowel movement and passes the feces out the anus.