Physiology of selenium and its application in feed
Selenium is not only an essential trace element for humans, but also for animals. Due to the toxicity of selenium and the low utilization rate of sodium selenite, adding excessive sodium selenite to feed may cause environmental pollution, thus limiting the application of inorganic selenium in feed. In 1984, the FDA lowered the upper limit of selenium addition to 0.1mg/kg, and organic selenium may be a safe and efficient selenium additive.
1. Selenium and the biochemical functions of animals
As we all know, selenium is the active center of glutathione peroxidase (GPx), which is an antioxidant enzyme that can quench or destroy free radicals and lipid peroxides in animals. Excessive free radicals and peroxides in animals will damage the cell membrane, causing cell dysfunction and necrosis. About 30-40% of selenium in animals exists in the form of GPx, as well as phospholipid hydroperoxidase, iodothyronine deiodinase (iodothy ronine deiodinase), also known as iodotyrosine deiodinase, is A selenium-dependent enzyme that can convert thyroxine (T4) into iodothyronine (T3). T3 is related to fat metabolism and heat control in animals. Therefore, animals with selenium deficiency have reduced resistance to cold. J·R·Arthur research shows that thyroid function also involves other 3 kinds of selenoproteins. That is, selenoprotein W, the loss of which will lead to sheep white muscle disease, increased drip loss of pork, broiler ascites, and may also have the function of antibiotics; selenoprotein P, which may be involved in the transport of selenium in plasma; sperm acrosome selenoprotein, in the cell It plays the role of framework and is the main component of sperm cells. Therefore, selenium is not only related to the growth of animals (thyroxine is the main growth hormone of animals), but also related to the reproduction of animals.
Wang Ruojun (1999) summarized the relationship between animal diseases and dysfunctions, selenium and GPx, and pointed out the related problems of selenium deficiency in animal diets (see attached table).
Second, the toxicity of selenium to animals
Long-term intake of 5-10 mg/kg selenium of various animals can cause chronic poisoning, which is manifested as emaciation, anemia, ankylosis, hair loss, hoof loss and affecting reproduction, etc. Ingestion of 500-1000 mg/kg selenium can cause acute or suboptimal toxicity. Acute poisoning, the light ones will stagger blindly, and the severe ones will die. Wang Hualang (1997) reported that the pathological damage showed hepatic necrosis, nephritis, renal congestion and upper respiratory tract ulcer. Some studies have confirmed that when cattle ingest selenium content of 400 ~ 800mg/kg feed, acute selenium poisoning can occur. The symptoms are: mild ataxia, special posture (lower head, ear hanging), increased body temperature, faster pulse, difficulty breathing in severe cases, bleeding from mouth and nose, severe diarrhea, and weakness. If it is not rescued in time, it may eventually die of respiratory failure. Chronic selenium poisoning can occur when calves eat feed with a selenium content of 3-20 mg/kg for a long time. Symptoms are: lameness, loss of vitality, deformed hooves, hair loss. The maximum safe amount of selenium for dairy cattle is 5mg/kg, and that for beef cattle is 8.5mg/kg.
Selenium is also an essential trace element for cattle. Calves with severe selenium deficiency can die acutely, mostly due to myocardial malnutrition and acute heart failure. Subacute mainly manifests as skeletal muscular dystrophy (leukmyopathy). Sick cows like to lie down and move lazily, with their elbows outstretched, their bodies lowered, their limbs stretched out, and their hoofs or heels or even ball joints touch the ground. When gaiting, the hind limbs should rotate to the right or draw an arc or goose step outwards, and cannot stand for a long time. Chronic selenium-deficient calves are stunted in growth, weak and emaciated, recurrent enteritis and diarrhea, long-term treatment, low body resistance, and reproductive obstacles such as overcoating during childbirth. Studies in the United States, Japan, France and other countries have shown that the minimum requirement of cattle is: 0.08-0.1mg/kg for dairy cows, 0.1-0.2mg/kg for beef cattle, 0.15-0.3mg/kg for piglets, and 0.1-0.15mg/kg for chicks. kg.
3. The importance of organic selenium to animal growth
The main advantage of organic selenium is that the content of available selenium is high, and its bioavailability is higher than that of sodium selenite. Austincanor (1973) reported that selenomethionine was four times more effective than selenite in preventing pancreatic degeneration in poultry, suggesting that organic selenium was more effective than inorganic selenium (sodium selenite). Cantor et al. (1975) observed that there were also differences in the bioavailability of various forms of organic selenium.
Scott (1973) of Cornell University in the United States tested the bioavailability of several selenium sources by using selenium supplementation to prevent chicken exudative diarrhoea. The bioavailability of sodium selenite is 100%, then alfalfa powder is 140%, and wheat It is 110%, corn is 83%, and fish meal is 35%. The bioavailability of selenium in fish products is low.
Ohio State University Mahan (1995) conducted a study on the utilization of inorganic selenium and organic selenium sources by pigs. The organic selenium source was supplemented with selenium yeast (selenomethionine) according to the dietary selenium level stipulated by the US Food and Drug Administration (FDA) (0.3mg/kg dry matter), the results showed that the selenium content in lean pig meat supplemented with selenium yeast was twice that of sodium selenite supplemented. It is further confirmed that the bioavailability of organic selenium is much higher than that of inorganic selenium. Feeding broiler chickens with organic selenium (Se─Plex50) can significantly reduce chicken drip loss and improve feather quality, which is very important for laying hens. Layers fed organic selenium in Japan kept eggs longer than those fed ordinary feed. Torrent (1996) reported that feeding selenium yeast to growing pigs reduced the occurrence of PSE pork and the pork tasted better. Suomi et al. (1992) also obtained similar results in Finland. When pigs were fed a diet with a selenium level of 0.4 mg/kg, the serum and liver selenium content of pigs supplemented with selenium yeast was significantly higher than that of inorganic selenium. Mahan et al. (1999) reported that organic selenium increased pig tissue selenium concentration, while the inorganic selenium group had higher drip loss and paler color. Wolter, B et al. (1999) reported that dietary selenium sources did not affect the growth performance of pigs, but organic selenium had the effect of increasing lean meat percentage.
4. The effect of selenium on animal immune function
Selenium can be used as a stimulator of animal immune system. Zhang Rui (1999) reported that selenium can promote antibody production, increase the titer of agglutinated antibodies in chickens inoculated with Newcastle disease vaccine, increase the number of cells that promote IgM production, and increase the number of peripheral leukocytes that are resistant to coccidiosis. Selenium deficiency in animals can reduce the lethality of polymorphonuclear neutrophils. Lyons (1995) reported that the results of fish research by the Finns showed that organic selenium has the effect of enhancing the efficacy of vaccination. Organic selenium may also promote broiler feather development by controlling the growth of certain viruses.
Selenium is one of the essential trace elements to strengthen the immune system and anti-infection ability of animals. Selenium deficiency in animals makes the structure of lymphoid organs loose, the number of phagocytic cells and lymphocytes decreases, and the proliferation of reticulocytes leads to different degrees of immune suppression or decline. Leukocytes have chemotaxis, phagocytosis and bactericidal effects. Hurley (1989) reported that when selenium is deficient, the GPx activity of leukocytes decreases, and the ability of leukocytes to kill microorganisms decreases, thereby reducing the resistance to infectious diseases. Boyne et al. (1984) injected selenium and VE to 5 selenium-deficient dairy cows. The results showed that the ability of polymorphonuclear neutrophils to phagocytize and kill Staphylococcus aureus in dairy cows injected with selenium and VE was significantly improved. Sutle et al. (1989) also found adverse effects of selenium deficiency on the immune function of anti-chicken animals. Supplementing selenium to dairy cows with low reproductive function can significantly reduce the incidence of metritis and prevent mastitis caused by E. coli in dairy cows. Droke et al. (1989) injected cattle with 25mg selenium and 340IU of VE, and the concentration of IgG antibodies produced by immunity to Pasteurella hemolyticus was significantly higher than that of cattle without selenium and VE or only injected with VE.
Erskinge et al. (1987) conducted a study on 32 herds of dairy cows and showed that herds with an average somatic cell count in the mammary gland below 150,000/ml had higher blood GPx activity and Se concentration, incidence of intramammary infection, and blood GPx activity and Se content were significantly negatively correlated. The results of Naiweni's (1991) determination of 9 groups of dairy cows also showed that there was a significant negative correlation between milk somatic cell counts and blood GPx and Se concentrations. Wicheel et al. (1994) reported that adult dairy cows supplemented with 2 to 4 rumen selenium pellets had significantly lower milk somatic cell counts than control cows. Forle et al (1987) reduced the rate of nutritional venereal diseases by 32%. These research results show that supplementing selenium to dairy cows and improving the nutritional status of selenium in the body can reduce the incidence of mastitis, thereby improving the safety and healthy survival of dairy cows.
Suttle & Fones (1989) research pointed out that the incidence of endometritis can be significantly reduced by supplementing dairy cows with dietary selenium. Jachens (993) subcutaneously injected 0.2mg selenium and VE60mg/kg body weight to calves aged 1 to 3 days in selenium-deficient areas. At the age of 4 weeks, the weight gain was significantly higher than that of the control group. The incidence of pneumonia was significantly lower than that of the control group, and the course of the disease was shorter, indicating that supplementing selenium to animals can enhance the body's disease resistance.
Jelinek et al. (1988) and Finch & turner (1989, 1990) respectively reported that selenium supplementation could improve the proliferation of lamb peripheral blood leukocytes stimulated by phytohemagglutinin (PHA). Cao et al. (1992) also reported that after cows were supplemented with selenium, the proliferation effect of peripheral blood lymphocytes stimulated by concanavalin A was enhanced. POllock et al. (1994) found that the proliferative effect of calf lymphocytes stimulated by hemocyanin was significantly higher than that of the control group. Many studies have proved that after animal selenium supplementation, it can not only promote the proliferation effect of lymphocytes stimulated by different mitogens, but also enhance the phagocytosis and bactericidal activity of lymphocytes and neutrophils.
Berenshtin (1972) first reported that supplementing rabbits with selenium increased humoral immune activity. Refett et al. (1988), Jelinlk et al. (1988), Ellis et al. (1990), Kadymor et al. (1990), Bires et al. (1993) supplemented selenium to calves, lambs, sheep, etc., and then planted influenza virus vaccines, distributed bacillus or Leptospira bacterin and Clostridium toxoid, observed the level of antibody production, and compared with the control group, the results showed that the serum immunoglobulin IgM concentration and antibody titer were significantly higher than those in the non-supplemented selenium group , 4 to 7 months later, the IgG antibody reached its peak.
Droke et al. (1989), Sabel et al. (1989), mishanin (1992), Nichoison et al. (1993) conducted comparative experiments with different animals, selenium yeast and sodium selenite, and further confirmed that selenium yeast (organic selenium) improves animal humoral immunity The function of selenium is better than that of sodium selenite, and the stimulating effect of selenium on humoral immune function has been affirmed. Blodgett et al. (1998) also confirmed that feeding weaned piglets with a diet containing 0.9ppm selenium, the serum antibody titer of piglets immune to lysozyme was significantly higher than that of the diet group fed 0.3ppm selenium, indicating that a certain range of concentrations of selenium Positively correlated with animal antibody levels.
Cao et al. (1992) reported that supplementing the diet of selenium-deficient dairy cows with 0.2 mg/kg of selenium significantly increased the production of 5-hydroxyarachidonic acid (5-hydroxyarachidonic acid) by peripheral blood lymphocytes stimulated by calcium ionophore (A23187). HETE) and leukotriene B4 (CTB4), if these two substances are added to the lymphocyte culture medium of cows, the proliferative effect on lymphocytes caused by hydrocortisone is partially relieved. It is deduced from this that the selenium status (concentration and properties) of the diet determines the selenium concentration of the tissue, and regulates the metabolism of arachidonic acid through the lipoxygenase pathway, thus affecting the proliferation of lymphocytes. One of the biochemical mechanisms of the proliferative effect.
5. Development and application of selenium-enriched organic feed
As we all know, only by adding a certain amount of selenium to livestock and poultry diets, can their normal physiological functions be exerted. At present, inorganic sodium selenite (NaSeO3) has been added to livestock and poultry diets to meet their needs. However, sodium selenite has certain toxicity, and the biological potency is also very low, and the residence time in the body is short, generally only 3 to 4 hours. Excessive supplementation is not conducive to food safety because of its toxic effect, and it is also a solution to the above problems. An effective method is a selenium-enriched yeast called "Sel─Plex50" bred abroad, which is rich in selenomethionine and has high biological potency and antioxidant properties. Add this selenium yeast to livestock and poultry diets , can improve its production performance and feed conversion rate.
Organic selenium additives, including methionine chelated selenium, organic selenate, selenium-enriched yeast, selenium-enriched algae, selenium malt, etc., have much lower toxicity than inorganic selenium, and have a longer accumulation time in tissues, such as selenium yeast, which are easy to produce , As long as the environmental conditions of yeast growth are changed and the level of sulfur is limited, various forms of selenium can be obtained. The final product is similar to high-selenium crops, which contain 50% selenomethionine, and the content of inorganic selenium can be ignored.
Nayloorgochoct (2000) reported that organic selenium (methionine selenium) and inorganic selenium (NaSeO3) were added to broiler diets at 0.25 mg/kg for feeding experiments. The results showed that the feed intake, feed conversion rate and mortality of the organic selenium group were 3730 grams, 1.71% and 3.5%, respectively, while those of the inorganic selenium group were 3825 grams, 1.79% and 4.5%, and the mortality rate decreased by 1%. Janyk (1998) added Sel─Plex50 selenium yeast to the diet of sows to increase the selenium content in milk, among which the selenium content in sow milk increased by 44%, and the selenium content in milk increased by 300%. get more selenium.
The high quality of livestock and poultry products is an inevitable trend in the development of the breeding industry. To realize the optimization of livestock and poultry products, the first thing to do is to achieve the high quality of feed and feed additives. In the past 10 years, due to the increasingly serious pollution in the production process of livestock and poultry products, vicious incidents of livestock and poultry products contaminated by feed have occurred continuously. Fear, the beef cattle farming industry is on the verge of bankruptcy, causing huge economic losses. Since then, there have been incidents of "Pork contaminated with Listeria" in Taiwan and Hong Kong. There is also Belgian chicken and egg dioxin (strong carcinogen) pollution, which is 800-1000 times more than the conventional one. It was later confirmed that the feed was contaminated by waste engine oil.
In my country's animal husbandry production, on the one hand, due to the abuse of antibiotic additives or feeding moldy feed or chemical additives (such as clenbuterol), on the other hand, due to the pollution of the environment by industrial "three wastes" and the extensive use of various pesticides in agricultural production, the The pollution of livestock and poultry products is becoming more and more serious. First of all, in terms of pesticide pollution, according to the survey in the past 10 years, the detection rate of BHC in pork, chicken, and eggs is 60% to 100%, and the rate of exceeding the standard is 87%, most of which exceed the standard by more than 9 times; the detection rate of DDT (DDT) 100%, exceeding the standard rate of 74%, exceeding 6.5 times the majority. The average DDT content in chicken in my country is 0.008-0.061mg/kg, in chicken fat is 0.534-2.5mg/kg, in pig fat is 0.820-6.785mg/kg, in milk is 0.05-0.16mg/kg, in fish meat is 0.5-2.0 mg/kg, therefore, the DDT content in human body fat has reached 1.4-2.0 mg/kg. In terms of heavy metal pollution, mercury, lead, arsenic, cadmium, etc., after polluting water sources and soil, are absorbed by plants and enriched in agricultural by-products, eventually endangering human health. There is a metal smelter in a certain place. The wastewater cadmium pollutes the irrigation water. The average cadmium content in the water is 0.67mg/kg, the farmland soil is 11.09%mg/kg, the rice is 1.13mg/kg, and the corn is 0.77mg/kg. Residents' cadmium intake is higher than the World Health Organization (WHO). 10 to 20 times the allowable amount increased, seriously endangering the health of livestock, poultry and human beings. The use of a large number of antibiotics and hormones has greatly enhanced the drug resistance of bacteria, causing a large number of fungi and molds to grow, polluting livestock and poultry products. The mold contamination rate reached 89.4%. The aflatoxin B1 (AFTB1) in the feed was measured up to 0.031mg/kg, with an average of 0.027mg/kg. This is a strong carcinogen, and the ultimate victim is human beings.
Organic selenium feed can improve animal immunity and enhance disease resistance. Selenium can antagonize the toxic effects of heavy metals such as cadmium, mercury, lead, and arsenic, and has a detoxification effect on aflatoxins, making them degrade and lose their carcinogenic effects. , It can also detoxify certain bacterial toxins, such as Fusarium toxin. The use of organic selenium feed does not require the addition of antibiotics and hormones. The feed and additives prepared from selenium-enriched green Chinese herbal medicine in Enshi high-selenium area have more disease-resistant and growth-supporting effects. It is an environmentally friendly, natural and organic, selenium-rich green product. The beneficiaries are not only livestock Animals, human beings are the ultimate beneficiaries.