Digestive System of Goats
The goat is a member of a class of animals called ruminants. These animals ruminate (chew their cud). Unlike us, they have special four-compartment stomachs especially designed to digest roughage (food high in fiber) such as grass, hay and silage.
The goat’s stomach has four chambers: 1) the rumen, 2) the honeycombed reticulum, 3) the omasum, and 4) the abomasum or true stomach.
The size relationship of the four chambers changes as the animal grows up. The abomasum gets proportionally smaller. To understand why this happens, let’s consider the function of each compartment and then review the goat’s diet.
The rumen acts as a big fermentation vat. Fermentation is the breaking down or digestion of food in the absence of oxygen. Bacteria and protozoa in the rumen supply enzymes to break down the fiber in the goat’s feed. This is similar to how bacteria can ferment the sugars in grape juice to make wine in big wine barrels. The tiny organisms in the rumen also help to build proteins from the feed and manufacture all of the B vitamins needed by the goat. Many nutrients that help provide the goat with energy are also absorbed here. The fermentation process produces heat that helps to keep the goat warm.
When roughage is eaten by the adult goat, it is chewed on, soaked with saliva, and then swallowed. The goat first swallows the roughage which then travels from the esophagus through the reticulum to the rumen. A matt of food particles forms on the top surface of the rumen. The micro-organisms in the rumen break down or ferment the food particles. The matt of food particles is essentially spread across both the rumen and reticulum. At regular intervals, the reticulum acts like a pump and squeezes any part of the matt floating in it to form a bolus. This bolus of food is called “the cud”. The cud is pumped back up the esophagus into the goat’s mouth for the goat to chew and re-chew and then swallowed again. Eventually, the cud drops back down permanently to rejoin the food matt in the rumen-reticulum where the parts of it that are small and heavy enough now settle out. This entire process is called rumination. If you watch the goat’s neck carefully, you can see the goat swallow and later regurgitate the cud. The goat will often burp to get rid of the gas produced by all the fermentation going on in the rumen. You can really smell the fermentation process on your goat’s breath. If something causes the goat to stop being able to burp up the gases, the gas will build up and bloat or swell up the rumen and your goat may become very sick with “bloat."
Once the food particles of cud become small, dense, and heavy enough, they drop to the rumen floor and pass permanently to the reticulum. Here, any foreign objects that may have been accidentally swallowed with the feed settle out in the honeycomb structure of the reticulum’s walls. Another name for the reticulum is the “hardware stomach” although it’s main function is to act like a pump. It now pumps these heavier, fermented particles over to the omasum.
The omasum removes the water from the fermented particles. The omasum also absorbs more nutrients from the food matt. These special nutrients are called volatile fatty acids. They help supply the goat with energy.
The particles are then forced into the abomasum or true stomach. Here, the particles are broken down or digested by the stomach acid, hydrochloric acid (HCl). This form of digestion is the same as what occurs in our stomachs.
The remaining particles are then passed on to the small intestine where most of the nutrients are absorbed by the body and made available to the goat.
When a goat kid is born, its rumen, reticulum and omasum are very tiny and not useful. Rather than eating solid foods, the goat kid depends on liquid, milk, for its feed source. When the kid swallows milk, the milk goes directly to the abomasum through the esophageal groove. Every time the kid swallows, a flap of skin at the entrance to the rumen folds over to form a grove that bypasses the rumen and sends the milk straight to the abomasum to be digested by stomach acid. As the kid gets older, the kid starts trying to consume roughage. The rumen becomes active and grows larger. Its population of micro-organisms increases. The reticulum and omasum also respond to the changes in diet by getting bigger. By the time the kid is an adult goat, roughage is its main source of food and its rumen is far larger than its abomasum.
Diagrams of goat kid (left) and adult (right) stomachs.
1 : rumen, 2 : reticulum, 3 : omasum, 4 : abomasum
- Get some human foods (for example, baby food, yogurt, rice krispies, shredded wheat, celery, spinach). Put a 1/4-cup of each in a separate unstarched cotton spice bag or square of cotton cloth. Boil them covered in a solution of 1 tablespoon of neutral detergent soap (i.e., baby shampoo) per cup of water in a saucepan for one hour. This will digest all the nutrients but the fiber from them. After boiling, rinse the bags in cold water, gently squeeze dry, and open. Which foods had more fiber? Which would be easiest for a kid to digest? *
- Do the same experiment using milk replacer, a complete pelleted calf or lamb ration, various grains, hays, and straws. Which ones have more fiber? For more advanced 4 - H er’s, weigh out 100 grams each of the feed samples rather than a 1/4 cup. After boiling, oven dry them at 500˚ F and reweigh them to compare fiber content.
- Watch a goat chew her cud. Try to count how many times a goat brings up her cud in 15 minutes. *
- Invite a veterinarian to come talk to your 4 - H group about bloat and other metabolic diseases that can occur when something goes wrong with your goat’s digestion. *
- A rumen fistula is an artificial opening that allows scientists to look inside the rumen of an animal. Contact an agricultural college that has a fistulated cow, sheep or goat and take turns examining the animal’s rumen.
- Obtain a clean and rinsed out digestive tract of a sheep or goat from a slaughter house and lay it out on a lawn to examine and identify the different parts. Measure the length of the different parts including the small intestine. *
* Activity is suitable for Cloverbuds to observe with adult supervision
Written by Suzanne Raupp, revised by Dr. tatiana Stanton