Effect Of Lactation Hormones On The Lactational Performance And The Mechanism In Dairy Cows

With the rapid development in china,the remarkable achievements of dairy industry were statisfied,especially through the optimization of feeding and management methods to improve the milk yield in the mid-lactation of dairy cows.However,how to persistent the lactation period,reduce mastitis and improve the quality of dairy products are still need further evaluated.Abundant research has focus on either how to elevated the milk production or the milk quality,whereas little research on the relevant hormones to prolactin how to modulation the lactation of dairy cows.The objective of the present study was to focus on the effects of domperdinoe,17?-estradiol,b ST and quinagalide on the milk production,hormone secretion and mammary gland gene expression of dairy cows,by the radioimmunoassay,ELISA,real-time fluorescence quantitative PCR(Quantitative Real Time PCR,q RT-PCR)and Western blotting,that will be better to understand the mechanism of lactation and maintain the persistent of lactation,which will also provide evidence for improving the lactation performance in dairy cows.The results are as follows:Effects of domperidone and milking frequency on the milk production,hormone secretion and mammary gland gene expression,the results showed that compared with 3 milkings,the milk production was significantly decreased(P<0.05)in 1 milking in dairy cows,nevertheless,the milk fat(P=0.04)and milk protein(P=0.05)content were decreased significantly in 3 milkings dairy cows.Injection domperidone could significantly increase the serum PRL concentration as well as milk PRL concentration was higher in 1 milking than 3 milkings(P<0.01).In milk fat,q RT-PCR results showed that compared to the 3 milkings dairy cows,expression of PRLRL,PRLRS and CSN2 were decerased(P<0.05)in 1 milking dairy cow.However,domperdione injections did not significantly affect genes expression relactive to the lactation between milk fat and mammary gland tissue.Milk production was decreased moderately by E2 injections during the treatment period(P<0.01).E2 injections increased basal PRL levels in serum(P=0.02)and milk(P=0.10),but did not affect milking-induced PRL release.Similarly,the concentration of IGF-1 was increased(P<0.01),but did not affect cortisol concentration during the treatment period.In mammary tissue,expression of Bcl-2(P=0.03)was down regulated and the Bax: Bcl-2 m RNA ratio(P=0.04)was higher by E2 injections.In milk fat,a lower tendency for the Caspase-3 and ACACA(P=0.06)m RNA levels were observed by E2 injections during the treatment period and the post-treatment period,respectively.There was no significant difference observed for the other genes in mammary tissue or milk fat.Western blotting showed that compared to the control cows,no effect of estradiol was observed with regard to the PRL receptors proteins level(P>0.10).BST injection could significantly increase the milk production of dairy cows(P<0.01),milk fat was increased(P<0.05)and the trendency for the milk protein(P=0.09)was observed in the treated cows.However,there was no difference of PRL concentration between serum and milk(P=0.46).Compared to the control cows,b ST could significantly increaed the basic PRL concentration in serum(P=0.03)and the PRL released during the milking was tended to be lower on day 8 of injection b ST(P=0.08).IGF-1 and GH were increased(P<0.01)by the b ST treatment,whereas no difference was observed on cortisol(P=0.15).q RT-PCR results showed that compared to the control cows,exprsssion of LALBA,CSN2 and PRLRLwere upregulated(P<0.05).Eighteen Holstein cows in mid-late lactation were used to determine if the responsiveness of the mammary gland to prolactin is affected by the concentration of the hormone.Compared to the control cows,the milk production was decreased(P<0.001)by the quinagolde treatment,milk protein was increased(P=0.02)and there was a treatment by day difference on milk lactose(P=0.05).After the treatments period,all cows received daily injections of 300 mg of domperidone,compared to the control cows,the milk production was greater in quinagolde cows(P=0.05)as well as the milk fat content Increased(P<0.01),the milk protein and milk lactose were tended to be greater(P=0.09 and P=0.06,respectively).In addition,the ECM was greater in quinagolide cows than the control cows(P=0.02).Injection quinagolide could significantly decrease the serum PRL concentration(P<0.001)and the PRL release(P=0.05).In milk fat,expression of Bcl-2(P=0.04)was down regulated and the Bax: Bcl-2 m RNA ratio(P=0.05)was higher by quinagolde injections.Furthermore,a lower expression of PRLRS(P=0.05)m RNA was observed by quinagolde injections during the treatment period.There was no significant difference observed for the other genes in milk fat.There was a significant effect of milk statsis on milk production of dairy cows(P<0.01).Compared with the control group,milk fat was significantly increased after 24 h miling stasis(P<0.01)in the post-treatment of milking stasis,the milk fat content(P<0.05)and milk protein(P<0.05)were significantly increased,but the content of lactose decreased significantly(P<0.05).q RT-PCR results showed that the effect of milk statsis on the genes relative to the lactation,compared with the control group,CSN2 m RNA expression increased significantly(P<0.05),the expression of PRLRL m RNA significantly increased(P<0.05)and LALBA m RNA expression was significantly decreased(P<0.05).Through the experimental results,the following conclusions were drawn:1.Injection of domperidone can significantly improve serum prolactin concentration;Domperidone combined with different milking frequency can be enhanced by the lactation reaction,the PRLR m RNA expression was increased andmilk yield and fat content were improved.2.Estrogen decreased the PRLR m RNA expression and milk production was also decreased.3.b ST could increased milk production and up-regulated the expression of PRLR,CSN2 and LALBA,which are related to milk fat synthesis in lactating cows.4 Quinagolide can significantly reduce the serum prolactin concentration,prolactin receptor and reduced sensitivity to the mammary gland,resulting in decreased milk production.However,quinagolide and domperidone had no effect on milk production and milk quality.5.Appropriate extension of milk stasis can improve the milk fat percentage.