What is the anatomy and physiology of cattle? Information on digestive system and external anatomy of a cow.
The anatomical structures of beef cattle and dairy cattle are identical. In fact, many years ago, a scientist reconstructed the skeleton of a champion beef steer and that of a champion dairy cow, and it was found to be impossible to tell the difference between the two skeletons without reading the labels.
The difference between beef and dairy cattle is in the degree of fleshiness and in the development of the udder. Beef cattle are bred to be blocky and thick in shape with smooth muscles and flesh covering the angularity of their bones. Dairy cattle are much thinner in their fleshing. Their hip bones, ribs, shoulder bones, and other points of the skeleton are usually prominent.
The most interesting parts of cattle anatomy and physiology are the digestive system and the mammary system.
Cattle are ruminants along with other animals such as sheep, goats, bison, deer, antelope, giraffes, and camels. As ruminants, cattle chew a cud and have a complex stomach especially adapted for eating large quantities of forages.
The location of the teeth in cattle is an interesting aspect of their digestive anatomy. Cattle have teeth for grinding in the rear of their mouths on both the upper and lower jaws. However, they have teeth only on the lower jaw in the front of their mouths. The upper jaws in front are covered with thick pads of cartilage. When cows eat grass, they wrap their tongue tightly around the stems and break the grass off between their lower teeth and the cartilaginous pads. For this reason, cattle do not crop plants as close to the ground as do sheep and other herbivorous animals that have biting teeth on both the upper and lower jaws.
Cattle have four stomachs: (1) a rumen, or paunch; (2) a reticulum; (3) an omasum; and (4) an abomasum.
Cattle chew their food only enough to moisten it and form it into masses suitable for swallowing. The swallowed portions go into the paunch and the reticulum. In both of these stomachs the food is mixed and softened and enormous numbers of special kinds of bacteria and protozoa start the process of breaking down the coarse stems and leaves of forage into food the cattle can use.
Later the cattle regurgitate or “cough up” balls of the partially digested food from the paunch and reticulum. These balls are known as cuds, and the cattle chew them thoroughly, swallow them, cough them up again, and chew them again. This repeated chewing is called ruminating. Cattle spend as much as eight hours a day ruminating their food, or chewing their cuds.
After chewing, the cuds are swallowed and pass into the rumen, where bacteria and protozoa continue to help cattle digest the large quantities hay and other forages that they eat. The nutrients of forages are enclosed in hard and thick cell walls of cellulose, and digestive fluids cannot easily reach the nutrients. Bacteria and protozoa attack the cellulose walls and break them down, thus permitting the digestive fluids to reach the forage nutrients. The microbrganisms also change the cellulose into simpler compounds that can be used by cattle as food. The action of the microorganisms also generates considerable heat, and this heat is sometimes helpful in keeping cattle warm.
After the action of the bacteria and protozoa is completed, the food products are passed on through the reticulum into the other two stomachs where digestion continues. After digestion is completed, the products are passed into the small intestine.
The stomachs of newly born calves are not fully developed for digesting grain and forage. For this reason, calves must be fed milk or milk substitutes. Their ability to digest coarse feeds gradually increases until at three months of age they are ready to eat the same feeds as the dairy herd.
Mammary System — Udder.
The udder of the cow is made up of four mammary glands, each of which is known as a quarter. The udder is suspended from the cow’s body by a strong central ligament that in some cows must support not only the empty weight of the udder but also more than 50 pounds (22.5 kg) of milk. Skin and connective tissues bind the sides of the udder to the cow’s body and restrict its movement when the cow walks.
Nutrients for making milk are brought to the cow’s udder by the blood in two large arteries which pass through the front and rear quarters and deposit the chemicals in the mammary cells. The blood leaves the udder in three large veins. Scientists estimate that 100 quarts (95 liters) of blood flow through the udder of a high-producing dairy cow in an hour.
The portions of the mammary glands in which the milk is actually secreted are filled with clusters of grapelike structures called alveoli. These alveoli are made up of tiny mammary cells that draw the chemicals from the blood, recombine some of them, and then secrete the result into the ducts in the form of milk.
The secretion of milk goes on continuously until the udder is so full that the pressure of the milk in the udder stops any more secretion. Once the pressure is relieved by withdrawing the milk at milking time, the secretion starts again.
“Let-Down” of Milk.
Successful milking of a cow depends on the dairyman’s skill in getting the cow to “let down” her milk. To do this, he must understand certain aspects of the cow’s behavior and physiology, particularly the effect of nervous stimuli on the udder.
Cows become used to the time when they are to be milked. They recognize the time by certain acts of the farmer, such as rattling the milking pails, washing the udder to get it ready for milking, or starting the engine of the milking machine. Any of these can signal the cow’s brain that it is milking time.
The nervous stimuli cause the brain of the cow to send signals to the pituitary gland at the base of the brain. The pituitary gland secretes a hormone called oxytocin that is carried through the blood stream to the udder. In the udder, oxytocin acts on the cells and literally forces the milk out into the main ducts. At this time, if the cow is milked immediately and rapidly, all the milk can be easily withdrawn. Most efficient farmers start milking each cow about one minute after washing the udder since they know it takes about one minute for the nerves, the brain, and the hormones to prepare the udder for milking.
If the farmer fails to prepare the udder properly and fails to milk the cow in accordance with her “let down” of milk, he not only has more difficulty in withdrawing the milk, but he seldom gets as much out of the cow as he would have with correct milking procedures. Also, if the cow is frightened or upset during milking time, another hormone, called epinephrine, is secreted into the blood stream. This hormone counteracts the oxytocin and the “let down” of milk either doesn’t occur or is stopped.
Additional hormones secreted by the cow also affect her ability to produce rnilk. At least one hormone brings about the development of the ducts in the udder, while others affect the growth of the alveoli and the milk-secreting cells. Hormones also are at least partially responsible for the fact that a cow produces the most milk per day during the second month after she calves.