Ruminant stomachs have four compartments: the reticulorumen, the reticulum, the omasum and the abomasum.


Reticulorumen                                                                                                                                                                                                                                                                      The reticulorumen represents the first chamber in the alimentary canal of ruminant animals. It is composed of the rumen and reticulum.


The second stomach of a ruminant, having a honeycomb-like structure, receiving food from the rumen and passing it to the omasum.


The muscular third stomach of a ruminant animal, between the reticulum and the abomasum.


The fourth stomach of a ruminant, which receives food from the omasum and passes it to the small intestine.


For the first two weeks of a calf's life, it is a monogastric animal that uses only the abomasum to digest the milk and milk replacer.

A monogastric animal has a simple single-chambered stomach.

The abomasum releases digestive enzymes that break down fats, carbohydrates and proteins. The energy requirement is provided by the absorption of glucose from the abomasum.

As soon as a calf drinks milk, this milk passes via the esophageal groove over the rumen to the abomasum. The abomasum makes up 60 percent of the stomach capacity in a newborn calf. At three to four months of age, the abomasum occupies 20 percent of the capacity, and as the animal matures, the abomasum shrinks to 8 percent of the stomach capacity.



The rumen is made up of an epithelial layer and a muscle layer. This muscle layer is responsible for rumen contractions and supports the epithelial layer, which provides absorption.

During rumen fermentation, propionate and butyric acid are formed. These provide a stimulus that is necessary for the development of the epithelial layer.


In order to wean successfully, the rumen must develop properly so that volatile fatty acids can be absorbed and metabolized.

Calves that do not eat roughage, grain and concentrates do not develop functional rumen. The crude fibers and grains develop the rumen and enable the calf to switch from a milk feed to a roughage / grain feed.


In a newborn calf, the rumen makes up 25 percent of the stomach capacity. The rumen develops through growth and changes in eating habits. The calf becomes a ruminant, and at three to four months of age, the rumen already occupies 65 percent of the stomach capacity. It is the most important part of the digestive system in a calf that eats roughage!



A calf is born with an esophageal groove, which consists of muscular folds from the reticulorumen that come together to bypass the rumen, reticulum and omasum through to the abomasum when the calf drinks milk.

The suckling reflex and milk protein stimulate the groove to open.


Prevent a calf from drinking water immediately after milk feeding!

If the calf nevertheless drinks water immediately afterwards, the esophageal groove remains open, allowing the water to flow into the abomasum.

This weakens the coagulation of the milk and the digestion by the calf. This must be prevented as long as the calf has not yet been weaned!


When a calf drinks milk or a milk replacer based from skim milk, this flows into the abomasum.

Within ten minutes, this milk forms a clot in the abomasum due to the coagulation of milk protein or casein, the enzymes pepsin and rennin and due to the presence of hydrochloric acid.

Other milk components, such as whey proteins, lactose and most minerals, separate from the curds and enter the small intestine quickly (with a volume of 200 ml per hour). The lactose digests quickly and thus provides direct energy to the calf (unlike casein and fat).

The clot is gradually absorbed by the blood stream over the next 12-18 hours.