Study On The Biological Function Of Zinc Selenomethionine As Feed Additive For Growing-finishing Pigs

Selenium,as an essential trace element for animals,has the functions of resisting oxidation,promoting growth and improving immunity.Adding selenium to diet is a common method in livestock and poultry production to meet the daily physiological needs of animals.Zinc selenomethionine(Zn-L-SeMet)is a new organic selenium source,and has the advantages of strong stability,high bioavailability and strong water solubility.In this study,animal experiment and in vitro cell experiment were carried out.A total of 216 crossbred pigs with the bodyweight about 25 kg were randomly divided into 6 groups,including control group not adding any source of selenium preparation,four organic selenium experimental groups with 0.1,0.2,0.3 and 0.4 mg Se/kg from Zn-L-SeMet,and one inorganic selenium experimental group with 0.3 mg Se/kg from sodium selenite(Na2SeO3).It would provide direct evidence for Zn-L-SeMet application in livestock and poultry production to exploring the effects of different levels of Zn-L-SeMet on growth performance,slaughter performance,meat quality and antioxidant capacity of growing-finishing pigs.In vitro,C2C12 myoblast cells were used to investigate the effects of different doses of Zn-L-SeMet on the expression of functional genes such as selenoprotein and antioxidant after normal culture or 0.5mM H2O2 stimulation,so as to provide a mechanism explanation for the role of Zn-L-semet in animal production.The animal experiment showed that:(1)Adding different selenium sources in dietary had no significant effects on production performance,such as daily gain,carcass traits,meat color parameters and intramuscular fat content(P>0.05),and significantly affected drip loss of longissimus dorsi muscle 36 or 72 hours after slaughter(P<0.05),and the lowest value was found in Zn-L-SeMet group supplemented with 0.3 mg Se/kg level.With the increase of Zn-L-SeMet supplemental level,the drip loss and pH of longissimus dorsi muscle at 36 or 72 hours postmortuary had a significant quadratic change(P<0.05).(2)With the increasing Zinc-L-SeMet added level,serum selenium and glutathione peroxidase(gsh-px)activity is linear or quadratic increase(P<0.05),50 kg weight stage total serum superoxide dismutase(SOD)activity increased linearly(P<0.05)at 50 kg weight stage,80 kg weight phase serum IgM linearly increased(P<0.05)at 50 kg weight stage,and 50 kg and 80 kg weight phase linear or quadratic elevated serum IgG(P<0.05)at 50 kg or 80 kg weight stage.The serum Se content starting from 0.2 mg Se/kg was significantly higher than that in 0.3 mg Se/kg sodium selenite group(P<0.05).(3)Se content of muscle in 0.3 mg Se/kg Na2SeO3 group had no significant difference from that in control group(P>0.05),and was significantly lower than that in Zn-L-SeMet supplemented with 0.1,0.2,0.3 and 0.4 mg Se/kg(P<0.05).Se content in liver and kidney was significantly lower than that in Zn-L-Semet supplemented with 0.3 and 0.4 mg Se/kg(P<0.05).With the increase of Zn-L-Semet supplemental level,the selenium content in muscle,liver and kidney were linearly or quadrically increased(P<0.01),the malondialdehyde(MDA)content in longissimus dorsi muscle was linearly decreased(P<0.05),and the activities of T-AOC and GSH-Px in liver were linearly increased significantly(P<0.05).Cell experiments in vitro showed that:(1)Without hydrogen peroxide stimulation,different selenium source preparations significantly affected the gene expression of GPX4,SELENOW,TXNRD2,NRF1 and TFAM in myoblast cells(P<0.05),and the gene expression of NRFl and TFAM had a quadratic change with the increase of Zn-L-SeMet dose(P<0.05).Compared with Na2SeO3,Zn-L-SeMet significantly decreased SELENOW and increased NRF1 gene expression level at the same dose level(P<0.05).(2)Under the stimulation of 0.5 mM H2O2 hydrogen peroxide,the expression of GPXl,GPX4,SELENON,NRF1 and TFAM gene in myoblast cells were significantly affected by different selenium sources(P<0.05).The expression of GPX1,GPX4,SELENON and TFAM genes showed significant primary and secondary changes with the increase of Zn-L-SeMet dose(P<0.05),and was higher in Zn-L-SeMet group than that in Na2SeO3 group at the same dose level(P<0.05).In conclusion,Zn-L-SeMet can be well absorbed and utilized,and was an effective dietary selenium source for growing-finishing pigs.Adding Zn-L-SeMet to dietary can improve antioxidant and immune functions,significantly increase serum and tissue selenium content and water holding capacity of muscle,and present the obviously better than that of inorganic selenium source Na2SeO3.Adding 0.1 mg Se/kg Zn-L-Semet could effectively increase the contents of Se in serum and tissues,but higher than 0.3 mg Se/kg had no further improvement on meat quality indexes.In vitro cultured myoblast cells,Zn-L-SeMet could more effectively promote the expression of antioxidant selenium protein gene.It is suggested that 0.1-0.3 mg Se/kg is the optimal dietary level of Zn-L-SeMet for growing-finishing pigs.