To keep sows at a high level of production over the life of the product, it is essential to meet the needs of its various nutrients. At different stages of the sow production cycle, the demand for trace elements varies greatly. In addition to meeting the growth and maintenance needs of the sow's own tissues, these trace elements also meet the needs of embryonic growth and lactation. In late pregnancy and lactation, the burden on sows is increased and the demand for various trace elements is greatest. If the level of trace elements in the feed is low or the utilization rate of these elements is low, the sows will use the elements deposited in their tissues to meet the production needs, which will easily reduce the production life of the sows (Mahan, 1990) and also cause abortion. A series of problems, such as the number of dead babies. Mahan and Newton (1995) compared the difference in mineral content between the average weaned litter after birth of 3 litters, which was greater than 60 kg and less than 55 kg, and the unborn sows of the same age, and found that most of the metals in the unborn sows were found. The element content is higher than that of the sows, and the sows with a nest size of 60 kg have the lowest metal elements. This may be an important reason for the decline in production performance of sows after the peak of litter size as the litter increases. In actual production, the level of trace element additives used in general farms is higher than the NRC recommended standard. However, due to the limited feeding of sows during pregnancy, the intake of trace elements may be less, and due to the results of modern breeding (the goal of selection is high lean meat growth, high sow production, etc.) sows during lactation It is difficult to eat enough nutrients to meet the needs of production, so it is necessary to strengthen the nutrition of trace elements in sows.
1 The effect of trace element levels on sow production performance
1. Selenium selenium is a component of glutathione peroxidase (GSHPX) and acts as an antioxidant against vitamin E (VE). The two have synergies, but they cannot be completely replaced. VE mainly prevents the oxidation of unsaturated fatty acids in cell membrane and plasma membrane to produce peroxide, and the main function of glutathione peroxidase is to remove hydrogen peroxide and organic peroxide which have been formed in the body. Selenium is present in many tissues of the body, but the amount of tissue deposition depends primarily on the level of organic selenium in the feed. When comparing organic selenium and inorganic selenium sources, it was found that inorganic selenium leads to higher GSHPX activity, and most of the organic selenium is absorbed into the body tissues and remains as proteins (Mahan et al., 1996). The mechanism of action of selenium on the reproductive aspect of sows is still unclear. Mahan (1974) reported that the amount of selenium deposited in primiparous sows could meet the needs of the first litter. Feeding low-selenium diets did not affect litter size, but in the subsequent production cycle, low-selenium diets were reduced. Production performance of sows. The placenta of the sow has the function of effectively transferring selenium to the fetus, increasing the level of selenium in the diet of the sow. The selenium content of the liver and serum is increased in the newborn piglets, and the activity of GSHPX is enhanced, and the level of selenium in the breast milk is also There was a significant increase in the level of selenium in the diet and a significant increase in the survival rate of the fetus (Chavez, 1985; Mahan, 1995). If the VE and selenium contents in the piglets are insufficient, iron poisoning is easily caused when the newborn piglets are injected with iron (Toller, 1973), while the VE and selenium contents in the sow colostrum are several times higher than those in the normal milk, so the piglets must be Eat colostrum. The levels of VE and selenium in the milk of sows decrease with the age of the sow (Mahan, 1994), so the level of selenium in the feed should be appropriately increased for the old sow.
1.2 Iron iron is a component of many functional proteins and has a wide range of functions. Ionized iron binds to the iron transporter and is transported by blood to various tissues and organs. The liver takes most of the iron from the plasma and stores it in the form of ferritin. The total amount of pig iron is very low. Because normal pigs store enough iron in the tissues, sows generally do not have iron deficiency. The higher iron requirement for pregnant sows than for unborn sows is due to fetal red blood cell synthesis. O'Connor (1989) compared the effects of adding 25 mg/kg and 125 mg/kg of Fe(FeSO4) on sow performance during sow pregnancy and lactation, and found no difference between the two groups. The amount of inorganic iron transported to the embryo through the placenta is very limited. The parent iron is transported to the fetus through the uteroferrin. The uterine transport protein is a glycoprotein. Although it can transport iron to the fetus, the amount of transport is relatively low. The iron in the milk is combined with lactoferrin, and the effect of increasing the level of inorganic iron in the sow feed to increase the iron content in the fetus and breast milk is not obvious. The possible reason is that supplementation with inorganic iron failed to increase the number of uterine transporters (O'Connor, 1989) and the iron saturation of lactoferrin (Mahan, 1989). When the piglet is born, the iron content in the body is about 54 mg, and the iron content in the breast milk is about 1.3 mg/L (Pond, 1978). For piglets, the iron requirement is higher because of its rapid growth rate and large amount of hemoglobin synthesis. The daily requirement for suckling pigs is 7 to 16 mg (NRC, 1998). Injecting iron into newborn piglets is now widely used to prevent anemia in piglets.
l. 3 Zinc and zinc play an important role in many enzyme systems and protein structures in animals. A typical symptom of zinc deficiency is skin keratosis, which is accompanied by a decrease in appetite and growth retardation. For sows, the uterus can be degraded, affecting the synthesis of milk (Fehse et al., 2000). The requirement for zinc in breeding sows is 50 mg/kg for NRC (1998). The bioavailability of zinc is affected by the levels of copper, iron, and especially calcium in the diet, and has a strong antagonistic effect on calcium. The demand for zinc in primiparous sows is high, and low-zinc diets do not affect the litter size of sows, but can lead to prolonged labor and increased number of malformations (Cunnare, 1982) Mahan (l990) points out that sows are fed high. Zinc diets produce more rapid weight gain after weaning than piglets fed low-zinc diets. Hill et al (1983) added 0, 50, 500, 5000 mg/kg Zn(ZnO) to the sow corn-soybean meal diet. The results showed that there was no difference in litter size between the sows in the sows, but the pigs in the wood plus zinc group. The incidence of skin and bone abnormalities was higher, with the lowest incidence in the 500 mg/kg group and the lowest in the 5000 mg/kg group.
1.4 Copper and copper are widely present in the enzyme system and are also present in some active proteins (such as metallotheinine). The sow's copper requirement is very low, and the NRC (1998) recommended standard is 5 mg/kg. The fertilization rate of sows is affected. During the sow's pregnancy, copper is mainly used to meet the needs of fetal growth and development, and the copper content in newborn piglets can be improved by supplying high levels of dietary copper to the sows, indicating that copper can be effectively transported to the fetus through the placenta. Insufficient copper in the sow feed, the plasma ceruloplasmin in the piglets decreased, and the number of dead pigs increased. There are many reports on the use of high-dose copper to promote pig growth, but the specific mechanism of action is still unclear. There are also reports of high copper use in sow diets. Cromwell (1993) reported that 250 mg/kg of copper (CuSO4·5H2O) was added to the diet during sow pregnancy and lactation, after 6 births until elimination. The results showed that the reproductive rate of gilts fed high copper was decreased, but the elimination rate decreased, and the litter size increased; the birth weight and weaning weight of piglets increased by 9% and 6%, respectively, and the weaning survival rate did not increase, from weaning to estrus The time interval was reduced by 1d, and the weight of the sow at 108d was significantly increased. Lillie and Frobish (1978) provided 15, 30, and 60 mg/kg copper to sows during four consecutive lactation periods. It was found that piglet birth weight linearity increased with increasing copper levels, and only 60 mg/kg group weaning weight And the survival rate has increased. High-dose copper is rarely used in sow diets in actual production.
1.5 Manganese manganese is an activator of many enzymes in the body, involved in oxidative phosphorylation and fatty acid synthesis in mitochondria, which is required for mitochondrial superoxide dismutase. Manganese activates alkaline phosphatase, promotes the synthesis of acid mucopolysaccharides in bones and cartilage, and promotes the utilization of body fat and inhibits liver degeneration. In addition, manganese can form a chelate with amino acids to participate in amino acid metabolism. A large amount of manganese can be stored in the bones and liver, and these manganese can be stably released when needed. The placenta also delivers manganese in a stable and rapid manner to meet fetal development (Gamble, 1971). The lack of manganese in animals can lead to abnormal bone development, and newborn piglets will have motor disorders. The lack of manganese in sows can lead to an increase in estrus, abortion and death.
1.6 Chromium chromium is widely present in animal tissues at low concentrations. The content of chromium in the general diet is generally at a level of 0.1 to 1.0 mg/kg. It is an essential component of glucose tolerance factor (GTF), which functions to promote insulin activity in chromium-deficient tissues, and thus the main physiological function of chromium is manifested by insulin (Davis et al., 1996). Chromium has an important influence on the performance of sows. Lindeman et al. (1994, 1995) reported that 200 μg/kg chromium was added to the primiparous sows from the growing season to the gestational period, which increased the number of piglets born and the weight of the weaned litter. The sow body tissue was more sensitive to insulin response. Campbell (1996) supplemented the sow with chromium in a single birth period. Although it was not found to increase the number of litters, the sow's ability to deliver was greatly improved, and chromium supplementation was found to reduce sow abortion and sow natural. Mortality increases the rate of return of sows. Mo Jingchuan et al. (1999) added 200 μg/kg yeast chromium to the sow diet and found consistent results. The effect of chromium on sow performance is mediated by enhancing tissue sensitivity to insulin. Exogenous insulin enhances the release frequency of luteinizing hormone (LH), promotes follicular development, and increases ovulation rate. The addition of chromium usually uses yeast chromium and picoplatin chromium, and the use of an inactive chromium source does not improve the sow's health and performance (Lindeman).
2 use organic trace elements to enhance the performance of sows
2. l Comparison of inorganic and organic trace elements In production practice, the addition of trace element premixes is often used to enhance the supply of trace elements to sows. However, inorganic trace elements usually have the following defects: the absorption rate is very low, generally only 2% to 10%, and most of them are excreted by animals to pollute the environment; inorganic trace elements are easy to interact with lipids and vitamins to promote the oxidation of fats and vitamins; The ionic metal elements are also susceptible to phytic acid, oxalic acid and cellulose in the intestine, which reduces the absorption rate. At the same time, the orange resistance between the elements also affects the biological potency; some inorganic trace elements have strong toxicity, such as Sodium selenite, if mixed unevenly in the feed, is prone to animal poisoning and poses a potential threat to the health of the production workers. The use of organic trace elements to enhance trace nutrient nutrition in sows is an effective method. Organic trace elements are a class of relatively stable compounds formed by the covalent bonding of metal ions with organic ligands (such as amino acids and sugars). Compared with inorganic trace elements, they are more expensive than the following, but have the following Advantages: It is more easily absorbed by animals. Because trace elements are closely combined with organic matter, they can be absorbed by the body through the absorption pathway of organic matter. Metal elements can be easily incorporated into peptides, amino acids or other organic matter and deposited into animal tissues. The ligands in trace elements protect minerals from other mineral elements and substances such as phytic acid when they are absorbed, and can reduce the toxicity of certain trace elements.
2.2 Effect of adding organic trace elements A number of experiments have confirmed that organic trace elements have a significant improvement in the performance of sows. Close (1998) reported that supplementation of 200 mg/kg ferritin during sow pregnancy and lactation resulted in increased birth weight and weaning weight, decreased mortality, and elevated hemoglobin levels in piglets. The reason may be that organic iron is more easily absorbed and can enter the embryo through the placenta and is effectively transported to the mammary gland. Mahan and Kim (1996) compared the effects of organic selenium and inorganic selenium on primiparous sows and their piglets. The results showed that the use of yeast selenium sows in colostrum and normal milk had higher selenium content, which made piglets have higher weaning. Serum, liver and eye muscle selenium concentrations. Both organic selenium and inorganic selenium can be transported through the placenta, but the transport efficiency of organic selenium is higher. Fehse and Close (1999) added complex organic trace elements (containing protein copper, zinc, iron, manganese and yeast selenium and chromium) to the standard feed of high-yield sows. The results showed that the performance of sows was improved compared with the control group. The litter size increased by 0.3, the number of live litters increased by 0.4, and the number of weaned pigs increased by 0.5. At the same time, the production period of sows was prolonged and the elimination rate decreased.
3 Conclusions
In general, because sows have low feed intake during lactation, they generally cannot meet the nutritional needs of sows and piglets, and trace elements play an important role in the performance of sows. Therefore, it is necessary to strengthen the mother. The micronutrient nutrition of pigs and the addition of organic trace elements in the diet are a feasible and effective method.
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