Continue to the topic of "three external forces and three internal forces" for antibiotic free piglet feed. In that article, we shared some clues about the choice of functional substances from the perspective of "three internal forces strategy".
"External force" is to protect the intestinal physical and immune barrier functions of piglets as much as possible, which includes the
1. reduction of materials that contains harmful substances, ie to use“clean diet”
2. maximization of nutrients digestibility, especially protein
3. reduction of possible harmful bacteria invading the intestinal epithelium (bacteriostasis).
Moreover, the digestibility of protein depends on the digestibility of raw materials and the digestion capacity of animals. Since the intestine of piglets is not well developed, the digestibility of the raw materials is of paramount importance.
1. Classification and characteristics of protein
Proteins can be degraded into simple form of proteins (including albumin, globulin, Histone, protamine, Prolamin, gluten, scleroprotein) and binding proteins (including nucleoprotein, glycoprotein, lipoprotein, chromoprotein, Metalloproteins, phosphoproteins).
The physical and chemical properties of simple protein are as follows:
A. Albumin: It is small in molecular weight, soluble in water, neutral salts, dilute acids and dilute alkalis, and can be precipitated by saturated ammonium sulfate. Albumin is widely distributed in nature, such as wheat albumin in wheat seeds, serum protein in blood and egg white protein in eggs, etc.
B. Globulin: Generally, insoluble in water, but soluble in dilute salts, dilute acids and dilute alkalis, and can be precipitated by semi-saturated ammonium sulfate. Bean globulin in soybeans, myosin in muscles, hemoglobin and immunoglobulins in blood belongs to this category.
C. Histone: Soluble in water or dilute acid. Histones are chromosomal binding proteins, rich in amino acids such as arginine and lysine, and it is a class of myelin basic protein.
D. Protamine: Soluble in water or dilute acid, it is a kind of protein with small molecular weight. Protamine include more basic amino acids but lack of tyrosine and tryptophan. It is a myelin basic protein. Protamine exists in mature sperm cells and binds to DNA, like a protamine of fish.
E. Prolamin: It is insoluble in water or dilute salt solution but soluble in 70-80% ethanol. Prolamin is mainly present in the seeds of gramineous plants, such as corn-zein and wheat-gliadin.
F. Gluten: It is insoluble in water or dilute salt solution, and soluble in dilute acid or dilute alkali. Such as rice gluten in rice and wheat gluten in wheat.
G. Hard protein: It is insoluble in water or dilute salts, dilute acid and dilute alkali. Hard protein mainly exists in skin, hair, nails, such as keratin, collagen, elastin, silk protein and so on.
2. Composition characteristics of commonly used feed protein
Protein raw materials, including vegetable protein, animal protein, and microbial protein, are the first type of protein supplies to feed.
Vegetable protein such as soybean series (soybean meal, etc), rapeseed meal, cotton meal, etc; animal protein such as meat series (meat meal, fish meal, chicken meal, pork meal, etc), plasma meal, milk powder, egg meal); and microbial protein such as yeast series protein.
Generally speaking, plant proteins are mainly globulin, with dense tertiary and quaternary structures, high content of β-sheets and random coils in the secondary structure, low protein solubility, and low digestibility. Animal protein mainly consists of myofibrillar protein and sarcoplasmic protein. The tertiary and quaternary structures have low density, high protein solubility and high digestibility.
Source: Wang Ruihong, 2016; Zhao Dongdong, 2009; Guo Yuanyuan, 2011
The second type that provides protein in feed is energy material. Due to the high dosage of energy materials in formula, the influence on the digestibility of protein provided by these cannot be ignored. Commonly used energy materials for feed such as corn, wheat (flour), broken rice, barley, sorghum, etc. These type of proteins in energy materials mainly include gliadin, gluten, globulin, and albumin. The proportion of different types of protein contained in different raw materials determines that the protein digestibility is different.
Source: Jia Xiangxiang, 2011; Zhang Fei, 2012; Li Ming, 2006
3. Main factors affecting protein digestibility
A protein with a high digestibility is potentially of a better nutritional value than one of low digestibility because it would provide more amino acid for absorption on proteolysis. There are several factors which directly and indirectly affect the protein digestibility. Some of the basic factors affecting protein digestibility are given below.
Fineness of the product
The degree of protein exposure
Solubility of protein
The complexity or tightness of protein spatial structure
Protein molecular weight
4. Protein digestibility of different raw materials in suckling piglets
The determination of raw material digestibility includes in vitro and in vivo methods. The in vitro method is fast and easy to operate, but it cannot truly reflect the digestion of raw materials in the animal body. The in vivo method is time-consuming and expensive, and the operation is complicated, but it can more realistically reflect the digestion of the raw materials in the animal body.
The digestibility of each protein materials in the feed raw material database is the ileum digestibility of piglets of 30 kg body weight. Due to the imperfect development of the intestinal tract of suckling piglets and the impact of stress on intestinal health, the digestibility of weaned piglets can be much lower than this.
We reviewed the articles and sorted out the apparent digestibility of commonly used protein materials in 6kg and 10kg piglets, for your reference.
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