| Selenium (Se) is the necessary microelement of human beings and animals. It is the protestant of life, which has triple biology function of nutrition, toxicity and detoxification.72% of the soil is Se deficiency in China, and the pastures and feed produced in it cannot meet the demands of Se by animals. The feed added mineral Se is poor safety, but the organic Se is costly. Therefore, the development and research of new Se source for feed become more and more important. Alfalfa (Mediacom sativa L.) is a kind of high quality feed resource that has strong ability to enrich Se, and The Enriched Se in plants mainly exists in the form of organic Se. Based on the soil science, plant nutrition, animal nutrition and feed theory, through applying the mineral Se to pastures, the Se can be absorbed, assimilated and enriched into pastures. And according to nutrition needs of livestock, Directly or adding the Se-rich pastures into feed to feed livestock, Thus it can reach the purpose of livestock safety production and supplying Se efficiently; and matching also Se-rich functional feed, to produce Se-rich animal by-products that meet the national《Tolerance limit of Se in foods》(GB13105-91). This research has important theoretical significance and application value to pasture, feed & animal nutrition and human health. So this paper was based on summarizing the domestic and international research progress of the relations of Se and plants, animal nutrition, then through the plant and animal experiments, it studies the nutrition effect of Se in the system of soil-pasture-feed-animal systematically, and preliminarily analyses the internal mechanism. The main research results are as follows:1. For alfalfa, spraying Se fertilizer on alfalfa leaves properly could significantly (P＜0.05) improve the absorption of Se, and improve the content of total Se, inorganic Se and organic Se. it was positively correlated with the application rate of Se; and it was also positive correlation among total Se, inorganic Se and organic Se of alfalfa;Se fertilizer application enhanced the conversion rate of organic Se and the utilization ratio of Se fertilizer significantly (P<0.05), and the conversion rate of organic Se and the utilization ratio of Se fertilizer increased first and then decreased with the addition of Se fertilizer,the conversion rate of organic Se of alfalfa was highest by spraying 100 mg Se kg-1, the utilization ratio of Se fertilizer of alfalfa was highest by spraying 50 mg Se kg-1,2.Addition of Se-rich forge in the basal diet could significantly (P<0.05)affect Se content of eggs, the Se content of eggs increased with the addition of forge Se content. However, the conversion rate of egg-Se ratio was negatively correlated with the forge Se content. The Se content of layer breast muscle, heart, spleen, liver and kidneys and other organs could be significantly (P<0.05) increased with the addition of Se-rich forge in the basal diet, being gradually increased followed by the addition of Se-rich forge. Addition of Se-rich forge in the basal diet could significantly (P<0.05) increase the Se content of layer blood, and the Se content of layer blood increased followed by the addition of the Se level of Se-rich forge. The Se absorption capacity of layer was gradually enhanced with time passing. Se absorption increased obviously as Se<2.319 mg kg-1 was added in the basal diet. Addition of Se-rich forge in the basal diet could significantly (P<0.05) affect Se uptake efficiency, which increased first and then decreased with the addition of the Se level of Se-rich forge. Se uptake efficiency was highest as 5.97mg kg-1 Se-rich forge was added in the basal diet, very significantly higher 722.46% than control group (P<0.01).3. it was very significantly (P<0.01)linear connection between Se rate and the content of pasture, feedstuff, dung,egg, tissue (Breast muscle, Cardiac muscle,Spleen, Liver, Kidney,blood).their linear equation as follows:The linear equation between foliar Se rate and Se content of pasture was y=0.0912x+0.7021(R2=0.9915);The linear equation between foliar Se rate and Se content of feedstuff was y=0.0118x+0.2199(R2=0.9867); The linear equation between foliar Se rate and Se content of dung was y=0.0137x+0.6817(R2=0.9926);The linear equation between foliar Se rate and Se content of egg was y=0.0023x+0.1993(R2=0.9904);The linear equation between foliar Se rate and Se content of Breast muscle was y=0.0011x+0.0783(R2=0.9593);The linear equation between foliar Se rate and Se content of Cardiac muscle was y=0.0016x+0.2740(R2=0.9466);The linear equation between foliar Se rate and Se content of Liver was y=0.0045x+0.5966(R2=0.9673);The linear equation between foliar Se rate and Se content of Spleen was y=0.0019x+0.7068(R2=0.9868);The linear equation between foliar Se rate and Se content of Kidney was y=0.0038x+0.6957(R2=0.9803);The linear equation between foliar Se rate and Se content of blood was y=0.0002x+0.0424(R2=0.9603).4. For alfalfa, applying the moderate Se base fertilizer could significantly (P<0.05) improve the absorption of Se, and increase the content of total Se, inorganic Se and organic Se, and it was positively correlated with the application rate of Se; and it was also positive correlation among total Se, inorganic Se and organic Se of alfalfa;The absorption of Se showed the inverted "V" type of rise-fall, the highest peak was in the initial bloom stage, but the content of Se in alfalfa decreased as the development of alfalfa growth stage. The contribution rate of alfalfa leaf Se for the total forage Se was more than 60%. Se fertilizer application significantly increased (P<0.05) the conversion of alfalfa organic Se, the organic Se conversion of alfalfa fertilized with Se was 40%～50% on the whole;and the conversion of alfalfa organic Se was above 50% when applying 0.45kg Se hm"2 or more, however the organic Se conversion of alfalfa fertilized without Se was no more then 40%.the conversion of alfalfa organic Se showed the declining trend as the development of the alfalfa growth stage.However, the application rate of Se fertilizer was very low, the utilization rate of Se fertilizer reached highest peak when applying 0.45kg Se hm-2, but it was also less than 1.5%; and the utilization rate of Se fertilizer increased first and then decreased during the whole growth period, the highest utilization rate of Se fertilizer was in the initial bloom stage.5 it was very significantly (P<0.01)linear connection between Se rate and the content of pasture,their linear equation as follows:The linear equation between base Se rate and Se content of pasture in the seeding stage was y=1.9912x+0.1827(R2=0.9696); The linear equation between base Se rate and Se content of pasture in the branching stage was y=1.7394x+0.1724(R2=0.9670); The linear equation between base Se rate and Se content of pasture in the bud stage was y=1.5045x+0.1542(R2=0.9694); The linear equation between base Se rate and Se content of pasture in the initial bloom stage was y=1.2547x+0.1588(R2=0.9835); The linear equation between base Se rate and Se content of pasture in the flowering stage was y=1.0044x+0.1500(R2=0.9904).6. The content of available Se in soil was improved by applying Se base fertilizer, and there was a positive correlation between the content of available Se in soil and the base application level of Se fertilizer, and the available Se content in soil was increased high significantly at the applying of 1.05 kg hm-2, and the available Se content in soil showed the trend to decrease with the growing-time of alfalfa above the applying of 1.05 kg hm"2, and the decreasing amplitude from 24.75% to 40.84%, and the content of available Se in soil in the seeding and the branch stage was significantly higher than that of bloom stage.7. Spraying Se fertilizer on alfalfa leaves could improve the yield, and the yield of alfalfa increased first and then decreased with the addition of Se fertilizer, the best amount of Se was 100 mg kg-1, the alfalfa field significantly (P<0.05) improved by 1623 kg hm-2 compared with the alfalfa without Spraying Se fertilizer. Spraying Se fertilizer on alfalfa leaves correctly could also significantly (P<0.05) improve the content and accumulation of crude protein and crude fat, and the best amount of Se was 100 mg kg-1, compared with that of the control treatment, the content improved by 13.84% and 48.07% and the field increased by 320.84 kg hm-2 and 140.97 kg hm-2 respectively;and the content and accumulation of crude protein and crude fat of alfalfa both increased first and then decreased with the addition of Se fertilizer,However, it had no significant effect on the content of crude ash and NDF, and the field reached highest value when Se was 100 mg kg-1, and it was significantly (P<0.05) higher than that of control. Moreover, spraying Se fertilizer on alfalfa leaves had no significant (P<0.05) effect on the content and accumulation of ADF and HF.Spraying Se fertilizer on alfalfa leaves appropriately could promote the absorption of phosphorus, potassium, zinc, copper, manganese, boron and molybdenum. For phosphorus, potassium and zinc, the best amount of Se was 100 mg kg-1, and the best amount of Se was 70 mg kg-1 for copper, manganese, boron. However, spraying Se fertilizer on alfalfa leaves could not significantly (P<0.05) promote the absorption of calcium and iron. The communication of phosphorus, potassium, zinc, copper, manganese, boron, molybdenum and iron increased first and then decreased with the addition of Se. Spraying Se fertilizer on alfalfa leaves increased the manganese content of alfalfa significantly (P<0.05), but the effect on the calcium and iron content was not significant (P<0.05). Applying the moderate Se base fertilizer could increase phosphorus, potassium, molybdenum, boron, zinc and copper content significantly (P<0.05), while the boron content decreased significantly (P<0.05) if the Se fertilizer was excessive. Phosphorus, potassium, zinc, copper, manganese, boron and molybdenum content of alfalfa increased first and then decreased with the addition of Se.8. The dry matter of alfalfa was increased significantly (P<0.05) by the application of Se base fertilizer, and it showed a increased first and then decreased trend as the amount of Se base fertilizer increased, the dry matter of alfalfa was highest in the treatment of Se base application 0.45 kg hm-2.and the dry matter accumulation rate in branch period and pregnant bolls was also raised, and that at the primary flowing stage was decreased. Dry matter accumulation rate of alfalfa showed the "W" pattern of rise-fall-rise-fall during the whole growth stage, and the peak values were in the branch period and primary flowing stage.The stem-leaf ratio of alfalfa was significantly (P<0.05) increased by applying the proper Se base fertilizer, and it showed a increased first and then decreased trend as the amount of Se base fertilizer increased, and the stem-leaf ratio was highest in the treatment of Se base application 0.45 kg hm-2. The stem-leaf ratio of alfalfa showed inverted "V" pattern of rising first and falling then during the whole growth stage and the peak value was in the branch period. The plant moisture content of alfalfa was not affected significantly (P<0.05) by the application of Se base fertilizer. The plant moisture content of alfalfa showed the decreased trend during the whole growth stage. Before the branch period, the plant moisture content of alfalfa were more than 80%, and after that, it decreased to about 70%. Applying Se base fertilizer could promote the growth of alfalfa, and the height of plant showed a increased first and then decreased trend as the level of Se fertilizer base application increased, and the plant was tallest when the base application level of Se was 0.45 kg hm-2. The growth rate of alfalfa showed inverted "V" pattern of rising first and falling then during the whole growth stage and the growing peak occurred in the pregnant bolls. Applying base Se fertilizer had different effects on the growth rate of alfalfa at different stages. Se fertilizer base application could promote the growth rate from seedling stage to pregnant bolls, and the highest growth rate occurred in the treatment of Se 0.45 kg hm-2, while it could decrease the growth rate from pregnant bolls to bloom stage.9. The crude protein content of alfalfa, which increased first and turned down later with the increasing Se fertilizer base application, was improved significantly (P<0.05) by applying the moderate base Se fertilizer. The treatment of base applying Se 0.45 kg hm-2 had the highest crude protein content. The crude protein content of alfalfa showed the "N" type change of rise-fall-rise during the whole growth stage, which appeared rising trend from seedling period to branching stage, declined from branching stage to initial florescence and increased from primary flowing stage to bloom stage. The crude protein content of alfalfa was the highest value in the branching stage.The contribution rate to total crude protein content of pasture came from alfalfa leaves were all above 65%, which were more than stalk. And the contribution rate of alfalfa leaves crude protein showed the inverted "N" type of fall-rise-fall during the whole growth stage, which reached the highest value in seedling period, secondly in primary flowing stage and the smallest in the branching stage.10. Applying the moderate Se base fertilizer significantly increased (P<0.05) the content of crude fat, which increased first and then decreased with the addition of Se fertilizer. The treatment of base applying Se 0.45 kg hm"2 had the highest crude fat content. The crude fat content of alfalfa showed the inverted "V" type of rise-fall in the growth period. The growth period of the highest peak of content of crude fat of alfalfa was delayed by Applying Se base fertilizer; The content of crude fat reached highest peak in initial bloom stage for the alfalfa fertilized with Se, while the alfalfa fertilized without Se appeared in bud stage. And the contribution rate of alfalfa leaves crude fat for the total forage crude fat was more than 50%, higher than stem.11. The effects of Se application as base fertilizer on crude ash content were different during different growth period. Applying the moderate Se base fertilizer increased (P<0.05) the content of crude ash in initial bloom stage and florescence stage, but it did not affect that in seeding stage, branching stage and pregnant bolls stage significantly (P<0.05). The content of alfalfa crude ash increased first and then decreased with the addition of Se fertilizer, and the highest peak occurred in the treatment of base applying Se 0.45 kg hm-2. The content of alfalfa crude ash showed the inverted "N" type of rise-fall-rise during the whole growth period. From the seeding stage to branching stage the content of alfalfa crude ash increased slightly and decreased from branching to initial bloom stage then increased slightly after initial bloom stage. And the contribution rate of alfalfa leaf for total forage crude ash reached 55% or more, higher than that of stem. Applying the moderate Se base fertilizer significantly increased (P<0.05) the contribution rate of leaf crude ash in branching stage, but it had no significant effects on that in seedling stage, pregnant bolls stage, initial bloom stage and florescence stage.12. The effects of Se application as base fertilizer on the NDF, ADF and HF content of alfalfa were different during different growth period. Applying the moderate Se base fertilizer significantly decreased (P<0.05) the NDF content in pregnant bolls stage, but it had no significant (P<0.05) effect on that in the other growth stage. The content of NDF of alfalfa fertilized with Se decreased first and then increased with the addition of Se fertilizer, and the smallest content occurred in the treatment of base applying Se 0.45 kg hm-2.The leaf NDF for the contribution rate of total forage was related with the growth stage, during the seeding and branching stage, the contribution rate were above 50%, but it was 40%-50% during pregnant bolls stage, initial bloom stage and flowering stage. Applying the moderate Se base fertilizer significantly decreased (P<0.05) the ADF content of alfalfa, which showed decrease first and then increase. The ADF content of alfalfa reached the lowest peak in the treatment of applying Se 0.45 kg hm-2. The ADF content showed the "N" type of rise-fall-rise during the whole growth period. The ADF content was increased from the seeding to pregnant bolls stage, but decreased from the bud to initial bloom stage, and then increased after the initial bloom stage. The contribution rate of alfalfa leaf for total forage ADF was related with in the growth stage. In the seeding stage, the contribution rate was above 50% only applying Se 0.45 kg hm-2. Applying Se 0.25 kg hm-2, 0.35 kg hm-2 and 0.45 kg hm-2, the contribution rate was all above 50%. While it all below 50% after branching stage. Above all, the contribution rate of alfalfa leaf for total forage ADF was increased first and then decreased, and the highest peak appeared in the branching stage. Applying the moderate Se base fertilizer could significantly (P<0.05) increase the HF content in the branching and flowering stage, but it had no significant (P<0.05) effect that during other growth stage. Se fertilizer rate could not significantly (P<0.05) affect the alfalfa HF content; The contribution rate of alfalfa leaf for the total forage HF was related with the growth stage. In the seeding, branching and initial bloom stage, the contribution rate was above 50%. In pregnant bolls stage, the contribution rate was above 50% only applying 0.75 kg Se hm-2 or more. In the florescence stage, the contribution rate of the leaf HF of alfalfa fertilized with Se for the total forage HF was above 50%, but the blank was below 50%.13. Applying the moderate Se base fertilizer could significantly (P<0.05) increase the P and K contents. The P and K contents were increased first and then decreased, and it reached highest peak with the Se fertilizer application of 0.45 kg hm-2. The contribution rate of alfalfa leaf P and K for the total forage P and K was related with the growth stage. In the seeding and branching stage, the contribution rate of alfalfa leaf P for the total forage P was more than 60%, and it was above 50% after the branching stage. The contribution rate of alfalfa leaf P showed the decreased trend by and large as the development of the alfalfa growth stage. In the seeding stage, bud stage, initial bloom stage and flowering stage, the contribution rate of alfalfa leaf K for the total forage K was more than 50%, but it was above 60% in the branching stage, The contribution rate of alfalfa leaf K increased first and then decreased by and large as the development of the alfalfa growth stage.and the highest peak appeared in the branching stage.14. Addition of Se-rich forge in the basal diet could significantly (P<0.05) increase the egg laying rate of layer, daily egg yield and decrease feed-egg ratio. With the addition of the forge Se content increased, the egg layinrate of layer and daily egg yield increased first then decreased, but feed-egg ratio is inverse.15. Addition of Se-rich alfalfa(SA) in the basal diet could significantly(P<0.05) increase laying rate, daily egg yield(P<0.05)and decreased feed-egg ratio(P<0.05); Addition of Se-rich yeast(SY) could also significantly(P<0.05) increase laying rate. There was no significantly(P<0.05)effect with addition of common alfalfa (CA), sodium Se (SS) or Se yeast(SY). Addition of Se-rich alfalfa (SA) was superior to SY, but it was significantly superior to CA and SS.16. Addition of SS,SY and SA in the basal diet could very significantly (P<0.01) increase the Se content of layer eggs; The Se content of layer eggs supplemented with SA was very significantly (P<0.01) higher than that supplemented with SS, but it was very significantly (P<0.01) lower than that supplemented with SY. The Se content of layer eggs increased with test time passing. The order of conversion ratio about the three Se source was:SY>SA>SS, they were very significantly lower than control. SS, SY and SA all could increase the Se content of the layers breast muscle, myocardial, liver, spleen and kidney. The Se content of layers'breast muscle, myocardial, liver, spleen and kidney supplemented with SY were significantly (P<0.05) higher than that supplemented with SS and SA, but the Se content of layers'breast muscle supplemented with SA was very significantly (P<0.01) higher than that supplemented with SS. The Se content of myocardial and renal were very significantly (P<0.01) lower than that supplemented with SS. The Se content of spleen and liver had no significant (P>0.05) difference with that supplemented with SS. In conclusion, as a source of Se, SA is much safer than SY. The Se content of breast muscle had no significant difference between basal diet supplemented with SS and CA, but that supplemented with CA was significantly (P<0.05) higher than that of control.17. Addition of SS, SY and SA in the basal diet could increase the Se content of layer blood very significantly (P<0.01), compared with SA, addition of SS and SY in the basal diet could increase the Se content of layer blood very significantly (P<0.01). Se source could significantly affect the Se content of layer manure, it was very significantly (P<0.01) higher than control. The Se content of layer manure that basal diet was added with SA was not significantly higher than that added with SY, but it was significantly lower than that added with SA. In the condition of that were same amount of Se, the SY absorption capacity was higher than SA. But the SY and SA absorption capacity was significantly higher than SS. The organic Se absorption capacity of layers improved with test time passing, and it tended to stable 21 days later. SS, SY and SA all could increase the Se absorption rate of layers very significantly (P<0.01). The group added with SY was slightly superior to that added with SA, and the group added with SA was significantly superior to that added with SS.18. Above all, alfalfa, as the largest planting area of forage in Henan province, is sensitive to Se, while most areas of there are very poor in Se element. Therefore, it is the necessary agriculture measures to increase the alfalfa yield and Se content and improve the quality by applying Se fertilizer. And The effect of spaying Se fertilizer on alfalfa leaves is far prior to apply Se as base fertilizer.For Se source, for example, just considering the ability of Se concentration of layer, the ability of three Se source is yeast Se (SY)> Se-rich alfalfa (SA)> sodium Se (SS). Speaking of the production capacity and safety of layer, Se-rich alfalfa (SA) is prior to yeast Se (SY). Therefore, Se-rich alfalfa (SA) can serve as a kind of high quality Se source additives used in livestock production. We can use the linear equation between Se rate and the Se content of pasture, according to Se nutrition need of livestock, and produce the different Se content pasture,the low Se content pasture may directly feed, and the high Se content pasture may act as Se source additives;Compared with the results of the paper, we think that adding the 30 mg kg-1～100 mg kg-1 of SA in diet can be used the regular additives, which increased the productivity of layer and increased the content of egg Se and organization Se greatly. It will get a good economic benefit. While adding SA more than 100 mg kg-1, we can obtain high forage yield and develop and produce a human egg and patch of Se functionality, which will not only make a good economic benefit, but also bring a better social benefits.
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