Effects Of Different Selenium Sources And Supplementation Levels On Feeding Of Heat-stressed Dairy Cows

This experiment was conducted to study the effect of sodium selenite and selenium yeast supplementation with different dose on physiological index,production performance,milk composition,serum biochemical,antioxidant,hormone,immune,ion content and concentrations in the serum and milk in heat-stressed cows.By this way,it assess the feeding value and confirm the best addition in dairy feeding for providing guidance basis in dairy production.Eighty healthy lactating cows(milk yield 25.3±2.0 kg/d,lactation period 167.4±28.3d,parity 1.4±0.6)were randomly assigned to 4 treatments according to a completely randomized block design.Treatments consist of 0.30mg/kg sodium selenite(A group),0.45mg/kg sodium selenite(B group),0.30mg/kg selenium yeast(C group),0.45mg/kg selenium yeast(D group)of dry matter(DM).Cows were fed by TMR and the experiment period lasted for 8 weeks with one week pre-trial period.The results showed as follows: 1.Daily average temperature-humidity index in the barn was more than 72,which indicated that the cows were subjected to heat stress during 10 weeks experiment period.2.The dietary selenium supplementation had no negative effect on the health of dairy cows under heat stress,but yeast selenium could significantly reduce the rectal temperature and respiration rate of the dairy cows compared with inorganic selenium groups(P <0.05).3.The effect of yeast selenium on feed intake and milk yield was not significant(P >0.05).There was no significant effect on milk protein,lactose,milk fat,total solids,urea nitrogen in milk(P >0.05),but the somatic cells decreased significantly with the dose increasing(P <0.05).4.Compared with inorganic selenium,the total protein,albumin,globulin,direct bilirubin,indirect bilirubin,total bilirubin,alanine aminotransferase,aspartate aminotransferase,creatinine,alkaline phosphatase,blood glucose and heat shock protein 70 concentrations had no significant effect when treated with selenium yeast groups(P <0.05).5.Compared with inorganic selenium,selenium yeast had no significant effect on insulin(P >0.05),but significantly decreased cortisol content(P <0.05).And it had no significant effect on T4 hormone(P >0.05)with the significant effect on T3(P <0.05).6.Compared with inorganic selenium,selenium yeast had no significant effect on serum IL-2,IL-4 and IL-6(P >0.05),and the same dose of selenium yeast and inorganic selenium had no significant effect on immunoglobulin A and G.However,the content of immunoglobulin A and G increased significantly with the dose increasing respectively(P <0.05).7.The activity of glutathione peroxidase and the total antioxidant capacity were significantly increased meanwhile the content of malondialdehyde were significantly decreased(P <0.05).But there was no significant difference in the content of total superoxide dismutase(P >0.05).8.Selenium yeast could increase the milk selenium content significantly(P <0.05),but had no effect in serum selenium.And selenium yeast could decrease the serum Cl and P content significantly(P <0.05)meanwhile have no effect in the content of serum Na?K?Mg?Ca(P >0.05).In summary,selenium yeast can significantly reduce the heat stress of cows respiratory temperature and rectal temperature with serum cortisol levels reducing and the content of T3 hormones increasing to relieve heat stress.It also enhance the body's antioxidant and immune capacity of dairy cows.No significant effect on dry matter intake and milk yield and composition,yeast selenium can significantly reduce the number of somatic cells and increase selenium content in milk.And with the increase of adding,the effect of somatic cells decreasing was significant.It has a positive effect to treat mastitis.Therefore,it is suggested that selenium supplementation could be used instead of sodium selenite for dairy cows under heat stress.The recommended dose is 0.45mg/kg(dry matter basis).