【Background and overview】

Zinc is one of the essential nutrients for animals to maintain life and growth, and participates in the composition and metabolism of various enzymes in the body. The development of zinc additives has gone through three stages: the first generation is inorganic salts, such as zinc sulfate and zinc oxide, and the second generation is some simple organic compounds, such as zinc lactate and zinc gluconate. However, the above two types of products all have application disadvantages. Inorganic salts not only have poor absorption and utilization rate, but also easily cause environmental pollution, waste of resources, and affect other active nutrients in the feed; and simple organic compounds are also difficult to overcome the low absorption and utilization rate. Defects, can not fully meet the needs of animal growth. The third-generation products are amino acid trace element complexes, such as protein zinc, glycine zinc and methionine zinc. A large number of tests have shown that zinc glycinate can improve the immunity of the body, provide animal production performance, and has no toxic and side effects. Compared with inorganic trace elements, it has the advantages of high bioavailability, fast absorption and good chemical stability. Inorganic zinc forms an ionic bond structure between anions and cations, while the zinc ion of a chelate not only forms a coordination bond with an amino acid, but also forms an ionic bond with its carboxyl group to form a five- or six-membered ring, and the zinc ion is enclosed in the chelate ring. , more stable, and the internal charge of the amino acid zinc tends to be neutral, forming a stable chemical structure. The amino acids in the chelate compound have a protective effect on metal zinc, which can prevent zinc from becoming insoluble compounds in the intestinal tract, so it has a high absorption rate and bioavailability. Inorganic zinc is less soluble in alkaline conditions (such as in the midgut of fish).

The high bioavailability of amino acid zinc may be caused by the formation of chelate between metal element zinc and amino acid, and the charge in the molecule tends to be neutral, which can maintain good stability in the digestive tract and is affected by other inorganic ions or antagonists. Small, not easy to combine with other substances to form insoluble compounds or be adsorbed on insoluble colloids. Two hypotheses for amino acid chelate absorption also address possible reasons for the higher bioavailability of amino acid zinc than inorganic zinc. It can better promote the production performance, immunity and antioxidant capacity of animals. With the continuous development of the feed industry and the introduction of relevant policies, zinc, as a highly specialized additive, will fundamentally change its product structure and technical content. Although in a certain period of time, feed additives still exist in various forms such as inorganic zinc, organic acid zinc and amino acid zinc, but from the perspective of saving resources and protecting the environment, the amount of inorganic zinc in feed will gradually decrease. The market space of amino acid zinc with high efficiency and high biological potency will become larger and larger, and it is expected to become the leading product in the zinc market of trace elements in the future. Only by reducing the price of organic zinc can it have a broader application prospect.

【Solicitud】

Today, amino acid zinc has been widely used in livestock and poultry industry and aquatic animals.

1. Effects on bioavailability

Amino acid zinc has better stability in the premix, and its damage to vitamin E and vitamin C is obviously less than that of inorganic salts. Zn-Met or ZnSO 4 was added to egg white or soybean-based refined feed, and the 1-year-old channel catfish were fed for 10 weeks. The results showed that in the egg white diet group, the supplementation of Zn-Met and ZnSO 4 was 5.58 mg, respectively. /kg and 18.94 mg/kg, the fish body could gain the maximum body weight. When the additions of Zn-Met and ZnSO 4 were 6.58 mg/kg and 19.91 mg/kg, respectively, the zinc content in the bones reached the maximum deposition amount; In the soybean-based diet group, when the additions of Zn-Met and ZnSO 4 were 5.91 mg/kg and 30.19 mg/kg, respectively, the fish could gain the maximum body weight. The additions of Zn-Met and ZnSO 4 The maximum deposition amount of zinc in bone was reached at 12.82 mg/kg and ≥80 mg/kg, respectively. Adding 1.5% phytic acid and 4% calcium phosphate to the semi-refined feed containing 30 mg/kg of zinc, and supplemented with amino acid chelated zinc or zinc sulfate, it was found that the weight gain of rainbow trout in the amino acid zinc group was significantly higher than that in the same group. Dosage of sulfuric acid group, the results show that the amino acid zinc still has a high biological advantage in the presence of phytic acid or calcium phosphate. The zinc content in rainbow trout (Oncorhynchus mykiss) fed with the amino acid zinc was significantly higher than that in rainbow trout fed with ZnSO 4 .

Experiments on broilers have shown that using growth rate and zinc content in tibia as evaluation indicators, adding zinc methionine in refined diets, semi-refined diets and corn-soybean meal type diets, its biological titers are respectively sulphuric acid monohydrate. 117%, 177% and 206% of zinc. Using zinc content in pancreas, zinc content in tibia and serum phosphatase of broiler chickens as evaluation indicators, it was found that the biological titers of zinc methionine were 133.93%, 108.35% and 105.94% of zinc sulfate, respectively. Using the crude ash weight, zinc content and daily gain of broilers as evaluation indicators, it was found that the bioavailability of methionine chelated zinc was 43%, 55.3% and 33.6% higher than that of organic zinc, respectively. However, the biological potency of methionine chelated zinc was found to be comparable to that of zinc sulfate in channel catfish. Recent studies have similarly contradictory results, showing that hydroxymethionine chelated zinc, compared with zinc sulfate, had no significant advantage in improving the growth performance of hybrid striped bass, but reduced serum zinc levels. The above studies demonstrate that organic zinc has an advantage over inorganic zinc in terms of bioavailability.

2. Influence on immune function

Organozinc and zinc sulfate were fed to L. vannamei, respectively, and it was found that organozinc could significantly improve the survival, growth and immunity of L. vannamei. Feeding dairy cows with zinc methionine reduces milk somatic cell counts and the prevalence of mastitis, and reduces the incidence of foot rot. Supplementing broiler chickens with zinc methionine and manganese methionine can reduce the incidence of coccidiosis in broilers and reduce the mortality caused by coccidiosis. In a test comparing the effect of zinc methionine on the immune function of animals, it was found that compared with the same amount of zinc oxide, zinc methionine can improve the immunity of chicks, sheep and weaned piglets. Adding amino acid zinc or zinc sulfate to the diet of laying hens, it was found that adding amino acid zinc between 55 and 59 weeks of age can reduce the mortality of laying hens and maintain a high level of antibodies.

3. The effect of antioxidant function

1.11 g rainbow trout were fed with 3 kinds of feeds containing different forms of trace elements for 15 weeks. The first feed was supplemented with ZnSO 4 , Mn SO 4 , and Cu SO 4 , and the second feed was Zn SO 4 , Mn SO 4 . and Cu-AA, and the third feed was Zn-AA, Mn-AA, and Cu-AA. The results showed that the alkaline phosphatase activity of the third feed group was significantly higher than that of the other feed groups, and the absorption effect of trace elements was also better than the former. two feeds. 40 mg/kg of zinc sulfate, 40 mg/kg and 20 mg/kg of zinc amino acid were added to rainbow trout feeds with a zinc content of 40 mg/kg, and these three feeds were denoted as SF, AM, AM-Hf, the results showed that the growth performance, enzyme activity and tissue deposition of rainbow trout in AM-Hf group were similar to those in SF group, while the alkaline phosphatase, DNA polymerase and CuZn-SOD activities of rainbow trout in AM group were higher than those in SF group. , tests have shown that the amino acid zinc is a more effective form of zinc supplementation. Similar reports have been reported on hybrid striped bass and red snapper. Studies have shown that the addition of the amino acid zinc can significantly increase the total antioxidant capacity (T-AOC) and glutathione (GSH) content in the liver tissue of 45-week-old eggs and reduce the production of tissue lipid peroxidation product, malondialdehyde (MDA). ; Significantly increased superoxide dismutase (SOD) activity and GSH content in spleen, and decreased MDA content.

Studies in mice showed that dietary zinc methionine supplementation significantly increased alkaline phosphatase (AKP), glutathione peroxidase (GSH-Px), T-AOC, total SOD, and Cu Zn- activity of SOD. Experiments have shown that the zinc content and AKP activity in the serum of zinc-deficient rats are reduced, the level of glutathione S-transferase in red blood cells is increased, the concentration of GSH is decreased, and the symptoms of red blood cell antioxidant insufficiency. In experiments in rats, moderate and high levels of zinc deficiency lead to oxidative damage to proteins, fats, and DNA, possibly due to a decrease in zinc-dependent antioxidant function. In addition, studies have also shown that zinc deficiency in rats can significantly reduce the content of GSH and SOD activity in blood and liver, and increase the content of MDA, and zinc supplementation can significantly reduce the formation of endogenous MDA. It can be seen that the amino acid zinc is an indispensable additive for maintaining the antioxidant system of the animal body.