Nutrients in pig feed and their basic functions

In order to maintain their own life activities, animals must ingest food from outside, and the food of animals is called feed. Most of the feed for livestock comes from plants, except for a few from animal, mineral and industrial products. Animals and plants are composed of chemical elements, and most of the chemical elements combine to form complex organic and inorganic compounds. To study the type and quantity of nutrients contained in feed, chemical analysis methods are generally used.

First, the classification of nutrients in feed

According to conventional analysis, the compounds constituting the animal and plant body are six components of water, crude ash, crude protein (CP), crude fat or ether extract (EE), crude fiber (CF) and nitrogen-free extract (NFE).

1. Moisture

The water in animals and plants exists in two states. It is contained in the cells of animals and plants, and is not tightly bound to cells, and is easily volatilized, which is called free water or free water. The other is closely combined with the colloidal substances in the cells to form a water film outside the colloid, which is difficult to volatilize. It is said to bind water or bind water. The sum of these two types of water that make up the body of an animal or plant is called total water.

2, coarse ash

After the residue is burned at 550 ° C, the residue is mainly minerals such as oxides and salts, and also includes sediment mixed with feed, so it is called coarse ash or mineral.

3, crude protein

According to the Kjeldahl method, the total nitrogen in the feed is determined, and the total nitrogen value is multiplied by 6.25, which is called the crude protein in the feed. The nitrogen content of most proteins is quite close, generally 14% to 19%, with an average of 16%. Therefore, by measuring the nitrogen content of the sample, the protein content can be calculated.

Protein content = sample nitrogen content × 100 / 16 = sample nitrogen content × 6.25

In animal and plant bodies, in addition to protein, there is a non-protein nitrogen. Therefore, the protein obtained by the nitrogen content measured as described above is generally called a crude protein.

4. Crude fat

The crude fat includes components (fat, wax, organic acid, ester-soluble pigment, fat-soluble vitamin, etc.) which are soluble in ether in the feed. Therefore, the crude fat is usually referred to as an ether extract.

5. Carbohydrate

Carbohydrates are the most important constituents of plant feeds, accounting for about 50% to 80% of dry matter, and are the main source of energy in animal diets. According to conventional analysis, carbohydrates can be divided into two parts, crude fiber and nitrogen-free extract.

Crude fiber (CF) is composed of cellulose, hemicellulose, polypentose and inlaid substances (lignin, keratin). It is the main component of plant cell walls and the most difficult to digest nutrient in feed.

Cellulose is an oligosaccharide formed by the glycosidic linkage of glucose molecules. It is chemically stable. Only under a certain concentration of sulfuric acid can the hydrolysis be achieved. Its nutritional value is similar to that of starch; hemicellulose It is the most widely distributed in the plant kingdom and can be hydrolyzed by dilute acid or dilute alkali; Lignin is the most stable and toughest substance. It is not a nutrient in plants. Its content affects the nutritional value of the feed. When the lignin content reaches 40%, the microorganisms can hardly be decomposed.

The CF content in the feed was negatively correlated with the digestibility of nutrients, but the CF measured by conventional analysis was lower than the actual content (some hemicellulose and lignin were hydrolyzed during acid-base treatment). To improve CF analysis, Van Soest (1976) proposed to use neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent wood cord (ADL) as indicators for determining fibrous substances in feed.

Nitrogen-free extract (NFE) is a nitrogen-free substance in the organic matter of the feed to remove parts other than fat and crude fiber. It is collectively called nitrogen-free extract or soluble carbohydrate, and contains monosaccharides, disaccharides and polysaccharides. Starch) and other substances. The most widely distributed sugars in plant feeds are monosaccharides and disaccharides. Monosaccharides are mainly found in the fruits of plants. They are generally low in feed; disaccharides are abundant in sugar beets; starch is a stock of plants. It is rich in seeds, fruits, roots and tubers of plants, such as corn starch, which has a starch content of about 70%.

Conventional feed analysis does not directly analyze nitrogen-free extracts, which are derived from the difference between the original sample weight and the sum of moisture, coarse ash, crude protein, crude fat, and crude fiber.

Second, the basic functions of various nutrients in the feed

The basic functions of various nutrients in feed can be attributed to three aspects.

(1) Structural substances as animals

Nutrients are constituents of every cell and tissue of an animal's body, such as bones, muscles, skin, connective tissue, teeth, feathers, horns, claws and other tissues. Therefore, nutrients are indispensable substances in animal life and normal production processes.

(2) As an energy source for animal survival and production

In the life and production of animals, the maintenance of body temperature, voluntary activities and production of products, the energy required is derived from nutrients. Carbohydrates, fats, and proteins all provide energy to animals, but they are most economical to supply carbohydrates. In addition to energy, fat is also the best form of energy stored in animals.

(3) As a regulating substance for normal functional activities of animal organisms

Vitamins, minerals, and certain amino acids and fatty acids in nutrients play an indispensable role in regulating animal organisms. If it is lacking, the normal physiological activities of the animal body will be disordered or even die.

In addition to the above functions, nutrients in the animal body, after a series of metabolic processes, can also form a variety of isolated products.