| The transition period is the most critical period of dairy cows.It is also a period of high incidence of energy metabolism in dairy cows,especially high-yielding dairy cows.Body fat was mobilized due to the increased demand for energy caused by the DMI reduction in the transition period,the late growth of the fetus and the beginning of milking.However,the NEFA from excessive mobilization of body fat in the liver is difficult to fully oxidize,and then esterification into TG in the liver and deposition,and ultimately lead to fatty liver and damage to liver function.These affected the health of the body and reduced production performance,and then resulted in great economic losses for the dairy farming.In this study,different doses of the selenium-and choline-enriched premix(SCP)were added to the transition dairy cows to study the performance,the blood bioehemistry,the disease incidence,the selenium level in blood,liver and milk,the antioxidant capacity,and the gene expression of key antioxidant protein and lipid metabolism protein in liver tissue.In this study,96 healthy Holstein dairy cows were randomly divided into 4 groups(24 animals in each group)according to the parity,body condition,age,expected date of calving and milk yield of last lactation period:Control,low dose group(LDG),medium dose group(MDG)and high dose group(HDG).The cows in each group was individually supplemented with 0,40,80 and 120 g/d of new premixes on the basis diet.The SCP was mixed with 1/3 of the TMR in morning.Pre-feeding period is from the-21d to-15d relative to calving,and the trial period from-14d to 28d relative to calving.1.Effects of dietary supplementation of SCP on performance of transition dairy cows:Daily dry matter intake(DMI),daily milk yeild from postpartum 4 d,weekly determination of milk composition,calving coefficient(CC),body weight(BW)and body condition score(BCS)at the beginning and end of the experiment were measured.The results showed that the differences of DMI,BW,BCS and CC amang treatment were not significant(P>0.05).Adding selenium-and choline-enriched premix(SCP)to the transition dairy cows did not affect the milk yeild,4%FCM,milk fat,milk protein,lactose,milk solids and milk nitrogen(P>0.05),but the milk yield of MDG and HDG was 1.8 and 1.6 kg/d higher than that of Control group,respectively.These results indicated that the addition of a certain amount of SCP had a positive effect on improving milk yield.In addition,the SCC of dairy cows in MDG was lower than the SCC of dairy cows in Control and LDG,but not significant,which indicating that the SCP had a role in reducing SCC of dairy cows.2.Effects of dietary supplementation of SCP on blood biochemistry of transition dairy cows:The tail vein blood was collected on-14,-7,0.7.14,21 and 28 d relative to calving,and plasma was separated from the blood and being used to determine the biochemical indicators in bood.The results showed that the difference of the level of blood glucose(Glu),free fatty acid(NEFA),?-hydroxybutyrate(BHBA),total cholesterol(TC),serum creatinine(Crea),total bilirubin(TBIL),direct bilirubin(DBIL),alkaline phosphatase(ALP),blood calcium(Ca)and phosphorus(P)among treatment were not significant(P>0.05).The blood triglycerides(TG),aspartate aminotransferase(AST),alanine aminotransferase(ALT)and serum urea nitrogen(BUN)in the MDG and HDG were significantly lower than those in Control and LDG(P<0.05),and the level of total blood protein(TP)was significantly higher than that of Control and LDG(P<0.05).There was no significant difference of all biochemical indicators between MDG and HDG group(P>0.05).The results indicated that the addition of SCP could effectively reduce liver injury and maintain liver function.The effective addition of SCP was 80 g/d per cow.3.Effects of dietary supplementation of SCP on selenium level in blood,liver tissue and milk of transition dairy cows:The tail vein blood was collected on-14,-7,0,7,14,21 and 28 d relative to calving and the selenium level in blood were determined.On the 14th day after calving,liver tissue samples were collected under fasting condition,and the selenium level in liver tissue was measured.Milk samples were collected daily at the ratio of 4:3:3 at morning:noon:evening,and the milk selenium level were determined.The results showed that the selenium level in blood,liver tissue and milk of MDG and HDG was significant higher than that of Control and LDG(P<0.05).There was no significant difference of selenium level in blood,liver tissue and milk between MDG and HDG groups(P>0.05).These results indicated that dairy cows supplemented with SCP can improve the seleniun level in blood,liver tissue and milk.4.Effects of dietary supplementation of SCP on antioxidant capacity of transition dairy cows:Liver biopsy was performed on 14 d relative to calving,and TG content and antioxidant index in liver tissue were measured.The results showed that the addition of SCP could significantly decrease the TG content in liver tissue compared with Control group(P<0.05).Compared with LDG,TG in liver tissue of MDG and HDG group also decreased significantly(P<0.05),but there was no significant difference of TG content in liver tissue between MDG and HDG group(P>0.05).The activities of total antioxidant capacity(T-AOC),total superoxide dismutase(SOD)and glutathione peroxidase(GSH-Px)in liver tissue of MDG and HDG group were significantly higher than those in Control and LDG group(P<0.05),while the levels of malondialdehyde(MDA)and hydrogen peroxide(H2O2)were significantly lower than those in Control and LDG group(P<0.05).There was no significant difference of these antioxidant index between MDG and HDG group(P>0.05).The results indicated that the addition of 80 g/d SCP to per cow could effectively improve the antioxidant capacity of dairy cows,and could effectively remove the TG in the liver tissue.5.Effects of dietary supplementation of SCP on relative expression level of mRNA of key protein of antioxidant and lipid transport in liver:Liver biopsy was performed on 14 d relative to calving,and the relative expression level mRNA of glutathione peroxidase 1(GPxl),glutathione peroxidase 4(GPx4),microsomal TG transfer protein(MTTP),and apolipoprotein B100(ApoB100)in hepatocyte were measured.The relative expression level of GPxl mRNA in cows supplemented with SCP were significantly higher than that in the Control group(P<0.05),and the expression increased gradually with the increase of the amount of new premix,but the difference among test groups were not significant(P>0.05).There was no significant effect on the relative expression level of CGPx4 mRNA among treatment(P>0.05).The relative expression level of MTTP and ApoB100 mRNA in MDG and HDG group was significantly higher than that in Control and LDG group(P<0.05),but there was no significant difference between MDG and HDG group(P>0.05).The results indicated that the addition of SCP to dairy cows could increase the relative expression of GPxl,MTTP,and ApoB100 gene in liver tissue,and the optimal dosage was 80 g/d per cow.Adding 80 g/head·d of SCP to the diet of perinatal dairy cow can increase milk production to some extent,can increase selenium content in blood,liver tissue and milk,and promote mRNA expression of GPxl,MTTP and ApoB 100 in liver tissue,thereby improving the body,s antioxidant capacity and promoting the health of the cow. |
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