Hey All AIPMT Biology Aspirants, read out the next AIPMT Biology Study material/ Notes of Ruminant Stomach, useful for AIPMT Biology.

Species like cow, buffalo, sheep, goat, deer, giraffe etc. are called as Ruminants. Ruminants are “Cud-chewing ” animals. Ruminants have four chambered stomach namely- Rumen, Reticulum, Omasum, and Abomasum.

Ruminant Stomach showing Four Chambers

• Ruminant stomach is specialized for digesting cellulose, not proteins.
• Yet cellulose is the main carbohydrate in the leaves and stems that ruminants ingest, animals do not produce the enzymes required to digest cellulose.
• Microbes like bacteria and protozoa, are present in rumen of these animals to ferment cellulose. Fermentation produces food both for these microbes and ruminants.
• Microbes living in ruminant stomach are an example of Symbiosis, in which members of two different species live in close contact with each other and get mutual benefit.
• Microbes that live in rumen include Methanogens, methane producing bacteria. E.g. Methanobacterium, Methanomicrobium, Methanobrevibacter.
• Rumen is the largest compartment.
• Reticulum, or “honeycomb,” is the part responsible for rumination (or cud chewing) and trapping hard, indigestible substances like rocks, nails, or wires that may be ingested by accident while grazing.
• Omasum acts as a gateway to abomasum. It sends large substances back to rumen and reticulum while allowing smaller, well-broken down substances to pass into abomasum.
• Abomasum is the “true stomach” and is very similar to human stomach, as it is responsible for producing acids and enzymes to break down food, and sends the chyme to small intestine.

Process of Digestion

1. Chewed food initially enters the Rumen where symbiotic bacteria digest cellulose to glucose with the help of enzyme cellulase. Rumen has an oxygen-free environment, and the symbiotic organisms produce ATP and fatty-acids from this glucose via fermentation. These fatty acids are absorbed as an energy source by ruminants.
2. Next to rumen is Reticulum. Animal regurgitates portion of the digested material into its mouth, rechews it and forms a “Cud”. It is to increase microbial action and to enhance further break down of food.
3. Now, reswallowed cud passes to Omasum, where water and some minerals get absorbed.
4. Finally food from omasum passes to Abomasum, which contains the ruminant’s own digestive enzymes and corresponds to a true stomach.

NOTE:  Gizzard is another type of modified stomach found in birds. Birds do not have teeth and cannot chew food into small pieces, but they swallow sand, small stones, seeds, nuts etc. These stones lodge in the gizzard . Gizzard is a muscular sac which contains grit and helps in mechanical digestion of food by pulverization. Birds also have a Crop between esophagus and stomach for storing food.

• Rabbits and some rodents perform Coprophagy (dung eating). Mutualistic bacteria live in the large intestine and cecum of these animals, while absorption of nutrients occurs in small intestine. So, nourishing by-products of fermentation by bacteria in the large intestine are lost within the feces. Therefore, these animals recover these nutrients by feeding on some of their feces and then passing the food through the alimentary canal a second time.