Abstract: Zinc is an essential element of animals and is called a "life element" because of its extensive physiological and biochemical functions in animals. Traditionally, zinc in animal diets has been added in the form of inorganic salts, but zinc added in an inorganic form has a low absorption rate and is prone to bismuth with other trace mineral elements. Zinc added in organic form can better solve the disadvantages of inorganic zinc in livestock production. This article reviews the biological functions of zinc, the biological characteristics of organic zinc and its application in livestock production.
Key words: zinc, organic zinc, biological characteristics, production application
In recent years, the application of chelated zinc or organic zinc in animal diets has been widely recognized. Because many reports have confirmed that the addition of organic zinc can promote animal growth, improve reproduction and health. In poultry diets, zinc is usually added in the form of inorganic salts. However, it is zinc organic or chelate rather than free inorganic zinc ions. Therefore, it can be inferred that the biological effect of inorganic zinc depends on its ability to be converted into biologically active organic zinc, which is closer to its action form in vivo, and its biological potency is higher than that of inorganic zinc. Organic zinc is stable in the digestive tract and does not form a complex that hinders absorption with other substances. It can be more efficiently transported from the small intestine villi to the cell epithelium and then converted into a biochemically functional form. Many animal nutritionists and feed science and technology workers have been searching for organic zinc preparations with high efficiency, safe side effects and good nutritional value. Among them, zinc lactate has become an effective and economical source of zinc in feed, especially for the production of organic animals. Products have broad application prospects [1].
1. Types of organic zinc
In actual production, there are several kinds of complex zinc, organic chelated zinc, protein zinc salt and polysaccharide zinc complex. The American Association of Feed Control Office defines different organic element products as follows: a metal amino acid chelate is a complex of a metal ion and an amino acid of a soluble metal salt, wherein the molar ratio of metal to amino acid is 1:3, forming a conjugated covalent bond. The average molecular weight of the hydrolyzed amino acid is nearly 150, and the molecular weight of the chelate is not more than 800; the protein metal salt is a complex of a soluble metal salt with an amino acid or a partially hydrolyzable protein; the metal polysaccharide complex is a soluble metal salt and a polysaccharide solution Complex. The development and sale of organozinc is based on their theory of better biological availability and closer to animal organisms than inorganic zinc [1].
2. The biological function of zinc
2.1 Zinc is a component and activator of various enzymes
Zinc is a component of more than 300 enzymes such as alkaline phosphatase and alcohol dehydrogenase in animals. Many enzymes are active in the presence of zinc and can achieve maximum enzyme activity. At the same time, zinc can maintain the structural configuration of the ligands of some organic molecules, and act as a coenzyme in the enzyme reaction [1].
2.2 regulate a variety of physiological and biochemical activities in the body
Molecular biology studies have shown that the zinc finger structure formed by zinc and cysteine ​​or histidine can exist on nuclear membrane proteins, transcription factors, and many proteins involved in gene regulation, transcription, expression, and cell proliferation of genes. , differentiation and so on play a regulatory role [1].
2.3 Maintain membrane integrity
Zinc can be combined with a sulfhydryl group on a membrane protein, a phosphate group of a phospholipid, or the like to increase the stability of the membrane. When peroxidative damage occurs, the sulfhydryl groups in the membrane are oxidized to disulfide bonds, and zinc forms stable sulfates with sulfur to prevent oxidation and protect the integrity of the membrane. Zinc plays a role in the growth, development, reproduction, immunity, neurodevelopment and material metabolism of organisms through these functions. When zinc is deficient, it shows: growth retardation, reduced feed intake, incomplete keratinization, skin damage, decreased immunity, impaired reproductive function, and increased mortality [1].
2.4 promote animal body growth
Zinc not only participates in the synthesis of various enzymes in animals, but also closely relates to the synthesis of nucleic acids and proteins, which can affect the division, growth and regeneration of cells. In young animals, zinc is involved in the composition of zinc-containing enzymes and the synthesis and action of hormones. When the animal is deficient in zinc, its thymidine kinase activity is reduced, which impairs DNA synthesis and cell division, and hinders the growth and development of the animal [2].
2.5 Improve animal immunity
Zinc plays an important role in maintaining lymphocytes and preventing parasite invasion. When coccidia and bacterial infections occur, the amount of zinc in the tissue is reduced. Zinc deficiency not only inhibits the proliferative response of T cells to lectin, but also reduces cell-dependent antigen-dependent antibody synthesis and proliferation of cytotoxic T cells. When pigs are deficient in zinc, their thymus gland is degraded. Pigs were fed with two feeds containing zinc 1 mg/kg and 100 mg/kg, respectively, and the thymus weights were 15 times different. When zinc is deficient, it also induces leukemia, leading to lymphopenia and adrenal atrophy, which reduces the immune function of the animal [2].
2.6 Improve livestock and poultry reproduction capacity
Zinc affects every period of reproductive process in male and female organs of animals. When the female bird is deficient in zinc, the hatching rate of the egg produced is lowered and the mortality rate is increased. When the sow is deficient in zinc, the piglets produced become smaller. Zinc deficiency can also cause male calves, lambs, gonadal dysplasia, and the effect on female ruminants and their offspring is not obvious [2].
2.7 promote bone growth
Zinc deficiency can directly or indirectly inhibit the division and maturation of primitive chondrocytes, normalization and differentiation of maturation and transformation, and thus affect the activation of mineralization and osteogenic potential, and also lead to decreased osteogenic activity of long bones and slower cartilage formation. , cartilage matrix increased. When poultry is deficient in zinc, a unique "bone shortness" occurs. When the piglets are deficient in zinc, the femur becomes smaller and the strength becomes weaker. When calves and lambs are deficient in zinc, they stand in an arched back, gather their limbs, and bend their hind limbs in an inner arc [2].
2.8 Promote appetite
Zinc deficiency often causes hyperplasia and parakeratosis of the oral mucosa and is easy to fall off. The exfoliated epithelial cells will cover up and block the taste buds of the tongue nipple, making it difficult for food to touch the taste buds, not causing taste, and thus affecting appetite [2].
2.9 Maintain normal structure and function of skin and mucous membranes
Zinc maintains the normal structure and function of animal skin and mucous membranes. When an animal is deficient in zinc, its hair is rough and accompanied by varying degrees of hair loss. Histological observation revealed that the skin was hyperkeratotic or incompletely keratinized, the epithelial cells were incompletely nuclear, and the density of collagen subcutaneous tissue was reduced. When the chicks are deficient in zinc, their feathers grow poorly and dermatitis often occurs [2].
3 Biological characteristics of organic zinc
3.1 Chemical structure stability
Inorganic zinc forms an ionic bond structure between anions and cations, while organic zinc not only forms a coordination bond with an amino acid, but also forms an ionic bond with its carboxyl group to form a five-membered or six-membered ring. It is this unique structure formed by the ionic bond and the coordination bond that makes the intramolecular charge tend to be neutral. Therefore, the organic zinc is not easily combined with other substances to form an insoluble compound or adsorbed on the insoluble colloid, thereby having good chemical stability.
3.2 High biological potency
Amino acid chelated zinc is not only the main form of the body's absorption of metal ions, but also an intermediate substance for the synthesis of proteins in animals. Amino acid chelated zinc has fast absorption, less biochemical processes, less energy consumption in the body, and higher biological potency.
3.3 Enhance immunity and improve disease resistance and stress resistance
Amino acid chelated zinc has the effect of enhancing antibacterial ability, improving immune response, promoting animal cell and humoral immunity, and treating certain enteritis, dermatitis, dysentery and anemia. In addition, the amino acid chelated zinc also has good anti-stress ability, and has good anti-stress ability under the stress conditions of inoculation, castration, excessive temperature and too low.
3.4 Good palatability and less adverse effects
Inorganic zinc has a special taste and thus affects the palatability of animals. In addition, the unstable nature of inorganic zinc is also easy to produce bismuth with other nutrients, and affects the acid-base balance of the gastrointestinal tract during digestion and absorption, which has adverse effects on animals. As an intermediate product of biochemical processes in animals, amino acid chelated zinc not only has good palatability, but also enhances the activity of enzymes in the body and improves the utilization of protein, fat and vitamins, thereby promoting the growth performance of animals.
4 Application of organic zinc in livestock production
4.1 Pig
Hoover added methionine zinc to the sow diet. The first mating rate of primiparous sows increased by 7.2% on average, the average number of live births increased by 0.37, the rate of stillbirth of primipara was decreased by 2.1%, and the survival rate of weaned piglets increased by an average of 2.9. %, the rate of stillbirth in the 2-8 birth-bearing sows decreased by 7.1%-29.6%, and the survival rate of weaned piglets increased by 3.1%-6.2%. Studies have shown that the addition of 250 mg / kg zinc methionine can increase the growth rate, feed intake and feed conversion rate of weaned piglets by 5%-8%, 3%-4%, 1%-11%, and the weight gain of 0.63 at the end of the nursery period. -0.90 kg. Sichuan Agricultural University Nutrition Institute conducted a comparative test of zinc sulfate and zinc lactate to assess their effects on pig performance and zinc excretion. The results showed that the addition of zinc lactate to the diet of growing and finishing pigs could increase the daily gain by 5.35% and increase the feed return by 3.3%. Numerous experiments have confirmed that the bioavailability of zinc lactate is higher than that of zinc oxide and zinc sulfate, and it can reduce the zinc content of pig manure [3].
4.2 Poultry
Yang Renqi et al [4] studied the effects of amino acid zinc and zinc sulfate on the production performance and eggshell quality of laying hens in actual production. The results showed that the amino acid zinc supplementation of 51-59 weeks old laying hens could not significantly affect the production performance of laying hens, egg production rate, egg weight, egg-to-egg ratio, etc., but it was more effective than zinc sulphate. The trend of chicken survival. The addition level and source of zinc have no effect on eggshell thickness, while the eggshell strength is linearly positively correlated with dietary zinc level. Zinc acid chloride can increase eggshell strength and reduce egg breaking rate more effectively than zinc sulfate. Amino acid zinc is significantly more effective than zinc sulfate in absorbing and depositing zinc in hens. The application of organic zinc to meat and poultry has a significant effect on improving the production performance of meat and poultry, enhancing immunity, increasing feed conversion ratio, and improving the quality of poultry meat.
4.3 Aquatic animals
Organic zinc can improve the production performance, feed conversion rate and survival rate of aquatic animals. Studies have shown that in the salmon feeding experiment, the addition of organic zinc can increase the weight gain by 37.2%-61.8%, and the feed coefficient from 2.4 to 1.4-1.7. In the tilapia test, the daily gain can be increased by 35.5%, the feed utilization rate increased by 24.2%, the survival rate increased by 8.3%, and the feed cost decreased by 24.3%.
4.4 Ruminants
Zinc methionine can affect the immunity of ruminants and their resistance to disease. The milk yield of dairy cows with zinc methionine was significantly higher than that of zinc oxide plus methionine. The average milk yield increased by 4.1%, which ranged from 1.0% to 7.0%, and the supplementation of methionine zinc to dairy cows during the dry period can significantly promote the hoof. Growth [5]. Even high-yield cows with zinc methionine can also increase milk production. Experiments at Colorado State University show that the amount of milk fed by zinc methionine compared to zinc oxide plus methionine is
35.4kg/head. Daily increase to 37.9kg/head. Day, an average increase of 7.1%. Feeding zinc methioninate not only increases milk production but also increases milk fat percentage [6].
5 Conclusion
As a new generation of high-efficiency green nutrition additives, organic zinc has the biological value unmatched by inorganic zinc, but its addition needs further research. Adding certain zinc complexes or chelates to animal diets can promote animal production, increase milk production, fertility and immunity, but it is not certain whether organic zinc is added or zinc intake is increased. The reason. Therefore, there are still some problems in the practical application of organic zinc, which needs further research and solution in the future: continue to study the mechanism of action of organic zinc, determine its site of digestion and absorption in animals and metabolic pathways; the optimal addition time and additives of organic zinc To explore the best dosage form, to study the best chelate structure suitable for animal body; to study new formula, new process, reduce the production cost of organic zinc; establish a new qualitative and quantitative detection technology of organic zinc products.
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