The Cow Digestive System
Cows have shared life with humans as domesticated animals since many years ago. Throughout history cows have always had a great economic importance all over the word, mainly considering the production of meat, milk and other dairy products, but also owing to the fact that cowhide can be processed into leather in order to produce belts, jackets, shoes, among other products. Cow’s dung is also much appreciated as fuel to produce electricity or as a fertilizer for agriculture.
Although they are generally known as cattle and colloquially as cows, it is necessary to clarify that cows are specifically female, while bulls are males; and when bulls are castrated they become oxen. Cows are large and robust quadrupedal mammals with an average weight of 750 Kg, a height that ranges from 1, 20 – 1, 50 Mts and a 2, 5 Mts length (regardless tail).
They have two horns, one of each side of their head, a thick and short neck, and a dewlap hanging below their chest. Their body is full of short hairs, with varied colors and patterns. For instance, cows’ fur may be single white, black, red, brown, yellow or gray, but also a compound of several of the previous colors.
Furthermore, they may have diverse shaped and coloured stains in the head, trunk and limbs. The end of his front and hind limbs is formed by two fingers coated with a hoof. Particularly females have a four teats’ udder under the belly; each teat is approximately 2 – 3 cm in diameter and 5 – 10 cm in length.
According to several sources they were first domesticated by Middle East and Indian people about 10,000 years ago. Nevertheless, there are other sources that affirm that domestication took place around 8,800 – 3,300 B.C. in the Nile Valley, Egypt. As one can see, a clear definition related to this issue has not been established yet.
In our opinion it would be a little utopian to establish an official date for the first domestication of cows, since this should have been a gradual process that might have taken place simultaneously in different locations. However, there is a consensus among scientists that it occurred at some point in the Neolithic, when humans ended their phase of nomadic hunters and began living in permanent locations. Of course, the typical human curiosity played an important role in the process of domestication, since this practice was transmitted not only between neighboring tribes, but even between those from remote areas.
Cows’ first feeding source is pasture; their diet principally comprises roots, stems, leaves and grasses. Being ruminants, cows have a quite interesting digestive system.
Cows’ Digestive System
All ruminants, including cows, are characterized by spending about eight hours a day ingesting pasture or forage. This is possible due to their capability for degrading forage’s carbohydrates that are pretty difficult to digest for other non-ruminant species. They perform food’s degradation by using a fermentative digestion, instead of using digestive enzymes.
These fermentation processes are carried out by various types of microorganisms that ruminants host in their stomach, developing a symbiotic relationship between these bacteria and the ruminants. Thus, it is important to keep in mind that when we feed cows, we are, first, feeding their microorganisms, and therefore, those microorganisms must count with a favorable environment in order to correctly contribute to cows’ nutrition.
This process requires that the fermented intake (cud) be brought back to the mouth and chewed again, so as to break even more the vegetal materia and favor digestion process, what is known as rumination.
Such fermentative digestions have required the adaptive development of the cows’ stomach. In general, adult cows’ stomach can take up to 75% of their abdomen. Moreover, the stomach and its content together stand up approximately for the 30% of the cows’ weight. Furthermore, there is a mistaken belief that cows have four stomachs.Actually cows have only one, but is divided into four chambers: reticulum, rumen, abomasum e omasum.
The abomasum, the rumen and the reticulum are significantly different form the stomach of non-ruminants animals, because they lack glands and are covered with keratinized epithelium. Generally speaking, the rumen, that is the biggest chamber of all, and the reticulum play a similar role, by enabling the mixing of food with saliva and separating them into liquid and solid stratum.
The solid stratum conforms into a mass that is brought back to the cows’ mouth where it is broken into small particles by chewing and swallowed again. Later, this digesta moves into the omasum that is in charge for soaking all the inorganic elements and water in to the blood torrent. Finally, the digesta passes to the abomasum, the only chamber that is analogous to the non-ruminants’ glandular stomach, where the digestion happens.
Interestingly, cows are born with a digestive system that resembles those of non-ruminants animals since the functional and structural point of view. This is linked with the fact that when calves are born they are in the same position as non-ruminants, they can only digest milk. Consequently, their stomach chambers are small, and milk goes directly from the esophagus to the abomasum.
So, about the first three weeks of life, calf’s nutrition depends exclusively on the intestinal absorption of glucose, what is similar to the non-ruminants. Next, between the third and the eight week the calf passes through a series of adaptative steps, such as changes in the function and morphology of their digestive system, as well as the development of their normal microbial flora. This way the animals begin eating solid food in small portions, while gradually developing its stomach. Finally, after eight weeks of life the four chambers are already well developed allowing the typical ruminant’s fermentative process of digestion.
A relatively recent problem associated with ruminants in general is linked to the fact that they have anaerobic bacteria in the rumen that produce methane. This methane is released by the ruminants to the atmosphere, being one of the most important factors that today affect the stabilization of greenhouse gases in the atmosphere, and consequently, global warming.
It is considered that only carbon dioxide contributes more than methane to this serious environmental problem. Particularly, cows account for approximately 73% of the whole methane produced by livestock in general. For this reason, scientists are working in new diets that could help address this complex issue.
Many people believe that a cow has four stomachs. However, what they refer to as ‘cow stomachs’ are just different compartments in the digestive system of a cow. A stomach can be defined as an organ where acids, enzymes and other compounds used for digestion are secreted so as to aid in the breakdown of food particles into molecules. It is therefore incorrect to say that there are four cow stomachs since cows basically have one stomach with four compartments. These compartments include reticulum, rumen, omasum and abomasum. Each of these compartments plays a particular role in the digestion of food consumed by a cow.
A cow is classified as a ruminant since it chews cud. This means that it only chews food enough to allow it to swallow. This partially chewed food is stored in the reticulum. In addition, there is collection of ingested particles that cannot pass through the digestive system. When the cow is resting, food stored in the reticulum is brought back into the mouth and chewed more thoroughly. This process is known as chewing cud. After the second chewing the food then goes to the second compartment known as the rumen. In this compartment, fermentation takes place as well as the break down of things such as cellulose, lignin, hemi-cellulose as well as fiber. The food then moves on to the third compartment known as the omasum.
In the omasum the main process that takes place is the absorption of water and some other nutrients that have already been digested in the other compartments. The last compartment is known as the abomasum or the true stomach. Here, enzymes and other digestive juices break down the rest of the food. Some people refer to these compartments as cow stomachs while others consider them an extension of the esophagus since no real digestion takes place here.