Relationship Between Growth Hormone And Ketosis In Postpartum HOLSTEIN Cows

Ketosis is a common metabolic disorder in postpartum Holstein cows which is caused by negative energy balance(NEB).Some endocrine hormones might play an important role in mobilizing the body reserves during cows’ NEB period.Due to the large amount of postpartum lactation of Holstein dairy cows,the nutrients including energy intake in the feed cannot meet the needs of the body for lactation.The nutrients of the peripheral tissues are preferentially given to the mammary gland where higher metabolic activities occur and led to the excessive mobilization of body fat,and excessive production of ketone bodies in the liver results in an abnormal increase in blood levels.Growth hormone(GH)/insulin-like growth factor-1(IGF-1)is the growth-promoting axes not only acts on the mammary gland to regulate milk lactation and milk quality but also influences the peripheral organs such as the liver to exert energy migration effects.GH is a multifunctional endogenous hormone and earlier studies related to GH were mainly focused on fat decomposition,inhibition of fat synthesis,and oxidation energy supply.However,the dynamic monitoring of GH during the occurrence of ketosis in dairy cows has not been reported.Excessive body fat mobilization during ketosis increased the concentrations of Non-Esterified Fatty Acid(NEFA)and enhanced the production of reactive oxygen species(ROS).The relationship between plasma GH level and oxidative stress in cows with ketosis remains unclear.Thus,it is imperative to study the dynamic changes of plasma GH in cows with natural ketosis,to analyze the oxidative stress and the correlation between the indexes during the onset of ketosis.The first study,the study aimed to characterize the plasma levels of GH,β-hydroxybutyrate acid(BHBA),and non-esterified fatty acid(NEFA)and glucose(GLU)in SK cows and healthy control(CON)cows,to measure the liver function test(LFT)indices in SK and CON cows,and finally the quantitative real-time PCR(q RT PCR)assay of candidate genes expressed in adipose tissues of SK and CON cows during 0 to 7 weeks postpartum.Three experiments were conducted in this study.Experiment 1 involved 21 Holstein cows(SK,11,CON,10)weighing 500–600 kg with 2–5 parities.Results showed that GH,BHBA,and NEFA levels were significantly higher and the GLU level significantly lower in SK cows than those in CON cows.Pearson’s correlation analysis revealed there is a significant positive correlation between GH with BHBA in SK cows and there is a significant negative correlation between GH and GLU,between GH and NEFA in CON cows.In experiment 2,A dynamic monitoring of LFT indices was examined.The indices were alanine aminotransferase(ALT),aspartate aminotransferase(AST),γ-glutamyl transpeptidase(GGT),total bilirubin(TBIL),direct bilirubin(DBIL),total protein(TP),albumin(ALB),globulin(GLOB)and albumin/globulin(A/G).The results showed the plasma levels of TBIL,DBIL,and GGT indices were significantly higher in SK cows and TP was significantly lower than those in CON cows.This suggests that the liver function was impaired in SK cows.In experiment 3,ten cows(SK,5 and CON,5)were chosen and their adipose tissue was collected.the m RNA expression levels of GHR and peroxisomeproliferator-activated receptor alpha(PPARα)genes were analyzed and found they were significantly upregulated in SK cows,while the m RNA expression of insulin-like growth factor-I(IGF-1),insulin-like growth factor-I receptor(IGF-1R),and sterol regulatory element-binding protein-1c(SREBP-1c)genes were downregulated in SK cows.It is concluded that the higher plasma GH levels in SK cows during postpartum might involve the initiation of body adipose tissue mobilization,resulting in the occurrence of ketosis.The second study,to determine changes in growth hormone(GH)within 5weeks postpartum and on the second day of ketosis(within 12 hours)in Holstein dairy cows,to investigate the dynamic changes of GH and metabolic and antioxidative indices BHBA,NEFA,GLU,catalase(CAT),glutathione peroxidase(GSH-Px)and malondialdehyde(MDA)in the plasma levels of dairy cows in SK and CON groups.The cows were categorized into the SK group with BHBA concentration(BHBA≥1.2 mmol·L-1)and the control(NK)group with BHBA levels(BHBA<1.0 mmol·L-1).The results shown the SK cows had significantly higher mean levels of GH,BHBA,and NEFA while lower GLU levels as compared to the NK group in postpartum 5 weeks(p<0.01).A positive correlation of GH with BHBA and NEFA(r=0.495,p =0.000;r=0.494,p=0.000)and significantly negative correlation was also observed with GLU(p=0.000,r=-0.535).GH was highest in postpartum during 2 weeks,meanwhile,its changes were the same as BHBA and NEFA,but GLU was the lowest in the postpartum 2 weeks.MDA level in SK cows was significantly higher than that of the NK Group(p<0.01);MY,CAT,BCS,and GSH-Px were significantly lower than that of the NK group.The correlation showed that GH was positively correlated with MDA(r=0.443,p =0.000),but GH was negatively correlated with CAT and GSH-Px in SK cows(r=-0.597,p=0.000;r=-0.610,p=0.000).Intraday study results showed that the level of GH,BHBA,and NEFA in the SK group were significantly higher than that of the NK cows,and GH level in the SK cows was significantly positively correlated with BHBA and NEFA respectively(r= 0.550,p = 0.000;r=0.663,p = 0.000),but the mean GLU level in SK cows was significantly lower than that of NK group and GH level negatively correlated with GLU level(r=-0.419,p =0.004).It was also found that the feeding time affected the plasma levels of each index,that is,the plasma level of GH,BHBA,and NEFA decreased,and GLU increased after 1h of feeding;while the highest plasma level of GH,BHBA,and NEFA and the lowest of GLU occurred after 4 hr of feeding.The third study was designed with the aim to detect the changes in the antioxidation index by adding different concentrations of BHBA(0,0.6,1.2,3.0mmol·L-1).The results showed that with the increase of BHBA concentration and culture time(0,6,12,24,48h),the activities of superoxide dismutase(SOD),CAT,GSH Px enzymes decreased,and the concentration of MDA increased gradually.The results of q PCR showed that the BHBA significantly downregulate the expression levels of GHR,IGF1,and IGF-IR and also lower the antioxidant enzyme such as CAT,GSH Px,and SOD.Conclusions:1.The dynamic changes of postpartum plasma GH level were revealed in natural ketosis of Holstein dairy cows.The correlation was identified between postpartum plasma GH level and ketosis related indexes of Holstein dairy cows.2.GH can regulate nutritional metabolism by acting on the liver.Liver function is impaired in cows with ketosis,TBIL,DBIL and GGT may be used as auxiliary indicators to detect bovine ketosis.3.The m RNA expression pattern of GHR in adipose tissue of ketotic cows was significantly higher than that of healthy cows.Therefore,GH may mediate PPARα through JAK2-STAT5 and up-regulate the expression of adipose oxidation-related genes.4.A severe oxidative stress occurred in ketosis cows,there was a significant positive correlation between GH and MDA level,there was a significant negative correlation between GH and CAT level,between GH and GSH-Px level.The changes of GH,oxidation and antioxidant indexes were identified,which might be related to the over-mobilization of fat regulated by GH.Through the correlation analysis and comprehensive study between GH and these indexes,we preliminarily concluded that GH may play an important role in the pathogenesis of postpartum ketosis in Holstein dairy cows.It may regulate the over-mobilization of body fat,cause liver function impairment and severe oxidative stress in the body.It provides scientific basis for the study and prevention of ketosis from different angles in the future.