The digestive system of cattle

1. The composition and function of the cattle stomach

The stomach of cattle is composed of 4 gastric chambers, namely the rumen, reticulum and valve. Stomach and abomasum. Feed flows through these four stomach chambers in sequence, and part of it returns to the mouth before entering the omasum for chewing. These four stomach chambers are not connected in a straight line, but are intertwined.

(1) Rumen The rumen volume of an adult cow can reach 151 liters and can store 136 kilograms of content. The functions of the rumen are:

1. Temporary storage of feed. Cattle store a large amount of feed in the rumen when eating. When resting, they regurgitate large feed particles into the mouth and slowly chew them. The chewed feed quickly passes through the rumen to provide space for eating feed again.

2． Microbial fermentation feed continuously enters and flows out of the rumen, and saliva also enters the rumen stably to regulate the pH. Microorganisms (bacteria, fungi and protozoa carry out different fermentations according to the type of feed, and the fermentation end products are absorbed and utilized by cattle through the rumen wall. Rumen microorganisms can digest crude fiber, decompose sugar, starch and protein; synthesize amino acids and proteins, synthesize B vitamins and Vitamin K.

In order to maintain the normal function of the rumen and synthesize B vitamins and proteins, tumor bacteria and protozoa need to continuously obtain nutrients from the diet, including:

(1 ) Energy In addition to slow-release energy such as crude fiber, cattle also need a certain amount of fast-release energy, such as sugar, molasses or starch. When raising cattle, an appropriate ratio of refined to coarse must be considered to match the diet to achieve optimal feed utilization. Reach the highest value.

(2) Nitrogen sources are divided into nitrogen sources with fast degradation rate (such as urea) and nitrogen sources with slow degradation rate (such as soybean cake). The right ratio of the two can make microorganisms grow the fastest. In production, the former is generally required to account for 25% and the latter to account for 75%.

(3) Inorganic salts. Sodium, potassium and phosphorus are the most important. If urea is used in the feed, sulfur and magnesium must also be considered. The trace element that is more important for the growth of microorganisms is cobalt, because cobalt is not only beneficial to the growth of microorganisms, but also a raw material for the synthesis of vitamin B12.

(4) Unknown factors are also called growth factors. For cattle, there are two important sources of unknown factors, one is alfalfa and the other is distiller's grains. Both can stimulate the growth of rumen microorganisms, but the specific substances that work are not yet known.

During the fermentation of feed by rumen microorganisms, large amounts of carbon dioxide, methane and ammonia are produced, as well as small amounts of hydrogen, hydrogen sulfide, carbon monoxide and other gases. Under normal circumstances, these gases are excreted through the respiratory tract. Sometimes cattle cannot expel gas in time, and rumen bloat will occur.

(2) Reticulum The reticulum is located in the front of the rumen. In fact, the two stomachs are not completely separated, so feed particles can move freely between them. The endothelium of the reticulum has honeycomb tissue, so the reticulum is commonly known as the honeycomb stomach. The main function of the reticulum is like a sieve. Heavy objects that are eaten along with the feed, such as nails and wires, are present in it. Therefore, American cowboys call the reticulum a "hard stomach."

(3) The omasum is the third stomach, and its inner surface is lined with tissue-like folds. The function of the omasum is not very clear. It is generally believed that its main function is to absorb water in the feed and squeeze and grind the feed.

(4) Abomasum The abomasum of cattle is also called the abomasum. Its function is the same as the stomach of monogastric animals, secreting digestive juices to moisten the chyme. The digestive juices of the abomasum contain enzymes that can digest some proteins but basically do not digest fat, cellulose or starch. Feed leaves the abomasum in a watery state and then reaches the small intestine for further digestion. Undigested materials are excreted from the body through the large intestine.

2. Rumination

Beef cattle ruminate for about 8 hours a day, and they need a calm environment when ruminating. Grinding the feed through rumination can expose a larger surface area of ??the feed, which helps microorganisms digest crude fiber. However, recent experiments have shown that rumination cannot improve digestibility, but can only increase the total amount of feed utilized by cattle, because feed particles must be small enough to pass through the rumen.

During rumination, each soft feed bolus (i.e., food bolus) takes less than 1 second to travel from the rumen through the esophagus to the mouth. Chew each bolus for about 1 minute and then swallow it all. Eating high-quality forage takes less time to ruminate and passes through the rumen quickly, so the feed intake is larger. It should be remembered that the amount of roughage consumed by cattle should not exceed the amount of rumination for 9 hours at most, otherwise it will easily cause digestive and nutritional diseases.

3. Calf’s stomach

When a calf is born, the rumen is the smallest and the abomasum is the largest. The digestive process is similar to that of monogastric animals. The milk the calf eats passes through the first two stomachs directly to the abomasum, which secretes prorennin and other enzymes that digest the milk. If the calf swallows too quickly, the milk may enter the rumen. At this time, due to the poor digestive function of the rumen, it is easy to cause digestive system diseases. When calves begin to eat small amounts of dry matter into the rumen, the rumen begins to develop and gradually reaches the volume of the rumen of adult cattle.

4. Composition of the cattle intestine

Like pigs and other monogastric animals, the cattle intestine is divided into two parts: the small intestine and the large intestine. The small intestine includes the duodenum and ileum; the large intestine includes the cecum, colon, and rectum.

B. Digestion and absorption of nutrients by beef cattle

1. Digestion and absorption of carbohydrates

Carbohydrates come from concentrates and mainly contain starch and Soluble sugar; the second is from pasture and other roughage, such as hay, crop straw and silage, which have a high crude fiber content. Carbohydrate feed is the main source of energy for beef cattle.

(1) Digestion of soluble sugars Soluble sugars mainly include monosaccharides and disaccharides, which are components of grain feed. Almost all of these sugars are fermented by microorganisms in the rumen to produce pyruvate, which is further decomposed to produce volatile fatty acids (VFA) and carbon dioxide. Volatile fatty acids are energy that ruminants can directly absorb and utilize, and can also be directly utilized by bacteria and converted into bacterial polysaccharides.

(2) Digestion of starch Starch is the main component of cereals and tubers of some crops, and has two forms: amylose and amylopectin. After starch enters the rumen, it is quickly broken down into maltose and glucose under the action of microorganisms. The rate of starch digestion is affected by the feed source and processing conditions. For example, heating can speed up the digestion of starch. The undigested starch in the rumen reaches the small intestine together with bacterial polysaccharides, where it is decomposed into glucose, which is absorbed and utilized in the small intestine.

(3) Digestion of crude fiber Crude fiber is a general term for cellulose, hemicellulose, lignin and pectin. About 45% is digested in the rumen and 10% is digested in the large intestine. Crude fiber The final product decomposed by microorganisms in the rumen is volatile fatty acids, and the crude fiber that reaches the large intestine is also degraded by the microorganisms that live there.

2. Digestion and absorption of fat

(1) Digestion and metabolism of fat in the rumen. After feed fat enters the rumen, three changes occur, namely hydrolysis and hydrogenation of the hydrolyzate products. Effects and fatty acid synthesis. Rumen microorganisms can hydrolyze fat into fatty acids and glycerol. The fatty acids are hydrogenated and saturated by microorganisms, and glycerol is further fermented and degraded to produce propionic acid. Rumen microorganisms can synthesize fatty acids of various structures.

(2) Digestion of fat in the small intestine Although rumen microorganisms have a certain digestive effect on fat, the main role is played by the small intestine. Under the action of bile and pancreatic juice, fat is completely degraded and absorbed in the posterior jejunum.

3. Protein digestion and absorption

(1) Digestion of protein in the rumen Feed protein is digested by microorganisms in the rumen, which can be divided into 4 processes:

First, proteolytic enzymes and peptidases secreted by rumen microorganisms hydrolyze ingested proteins into peptides and free amino acids;

Second, free amino acids are directly utilized to synthesize microbial proteins or Other components of microorganisms, such as cell walls and nucleic acids;

Third, amino acids are continued to be decomposed to produce volatile fatty acids, carbon dioxide and ammonia;

Fourth, ammonia is used to synthesize microorganisms protein.

About 60% to 80% of feed protein is degraded in the rumen, and the remaining 20% ??to 40% directly enters the abomasum and small intestine;

(2) Non-protein nitrogen (referred to as non-protein nitrogen, NPN) feed is stored in the rumen The most widely used non-protein nitrogen in digestion is urea. Urea is decomposed into ammonia and carbon dioxide under the action of microbial urease, and ammonia is used by microorganisms to synthesize bacterial protein. However, the decomposition rate of urea in the rumen is too fast, the utilization efficiency is low, and ammonia poisoning is prone to occur. Methods to improve the utilization efficiency of urea feed include:

1. Slow down the decomposition rate of urea in the rumen so that microorganisms have sufficient time to utilize it. Currently commonly used methods include: ① Using non-protein nitrogen that decomposes slowly as feed, such as biuret, triuret, etc.; ② Using protective agents to Sulfur, wax and certain chemical polymers wrap urea to slow down its degradation rate, which is more effective. The "gelatinized starch urea" currently used in production is made by crushing starch-rich grains such as corn, sorghum, and barley and mixing them with urea to form a mixture equivalent to 40% to 70% of crude protein content, which is then gelatinized Products obtained from processing. ⑧ Use rumen microbial urease inhibitors to reduce the activity of urease and slow down the decomposition of urea, thereby improving the utilization efficiency of urea and avoiding ammonia poisoning. Urease inhibitor technology is an international new technology in the 1990s. It has the advantages of low cost, obvious effect, and easy industrial production. The Animal Husbandry Research Institute of the Chinese Academy of Agricultural Sciences has achieved certain research results in this regard.

2. Enhancing the synthetic utilization ability of microorganisms includes: ① Different types of microorganisms have different abilities to utilize urea. Therefore, when feeding urea, you can gradually increase it from less to more, so that the rumen microorganisms can gradually adapt. After 15 days, it will be safe to feed a larger amount of urea. . ② In addition to ammonia, many other substances are also needed by microorganisms to synthesize their own bacterial proteins, among which energy is the most important. Among different carbohydrates, cellulose is fermented too slowly and provides insufficient effective energy. Sugar fermentation is too fast and it is difficult to synchronize with the production of ammonia. Starch can better achieve the above purpose. Carbohydrates not only provide energy, but also provide a certain number of carbon skeletons required for the synthesis of amino acids. In addition to energy, the diet should contain a certain amount of true protein and the mineral element cobalt. In addition, when the amount of urea is large, a certain amount of sulfur should also be considered to meet the needs for the synthesis of sulfur-containing amino acids.