| Recent studies have shown that amino acids are not only the substrates for protein synthesis,but also regulate protein synthesis.Recent studies have shown that Met,Thr,Ile and Leu can regulate the rate of casein synthesis and affect the phosphate state of the mTOR signaling pathway in vitro.In this study,we investigate the mechanism of the effect of these four EAA on the synthesis of milk protein in the complex environment of dairy cows.This experiment was conducted with 10 Holstein cows in a replicated 5 x 5 Latin square design trial with 19-d periods.The treatments included: 1)a standard diet containing 16% crude protein [CP,High Protein(HP)];2)a 12% CP diet [Low Protein(LP)];3)LP plus RP Met(5g/d);4)LP plus RP Met+Thr(16.1g/d);5)LP plus RP Met+Leu(30.9g/d)+Ile(18g/d)+Thr.We study the milk protein yield,plasma concentrations of AA,hormone concentration and effect of signaling pathways in the mammary tissue.The results of this study showed that the milk yield of HP and MTILwas significantly higher than other treaments(P < 0.01);the rate of Milk protein,milk fat and milk lactose is not affected by treatment.In terms of milk protein yield,HP group is significantly higher than other treatment groups(P < 0.05);the yield of Lactose in high protein was significantly higher than MT group(P < 0.01);the MUN of HP group is significantly higher than other treatment groups(P < 0.01).High protein group of DM,OM and CP intake is significantly higher than other groups(P < 0.01).In terms of DM and OM apparent digestibility,HP group was significantly higher than other groups.The apparent digestibility of dietary CP(P = 0.08),NDF(P = 0.58)and ADF(P = 0.46)was not significant difference.HP group intake-N,milk-N,urine-N,fecal-N and total excretion N are significantly higher than other groups(P < 0.01).Nitrogen efficiency of HP group was significantly lower than other groups(P < 0.01),however,urine nitrogen efficiency is significantly higher than other groups(P < 0.01).HP group and the MTIL group have a significantly higher plasma urea nitrogen than the LP,M and MT three groups(P < 0.01).The group Met concentration was significantly lower than other groups(P < 0.01),and the high protein group Val concentration is significantly lower than other groups(P < 0.01).The HP group and the MTIL group of Leu,Arg are higher than other treatment groups(P < 0.01).Plasma concentrations of Thr,His and Phe are not affected by treatment.High protein concentration of urea is significantly higher than other treatment group.Insulin,glucagon and growth hormone concentration is not affected by the diet treatment.Low protein diet of IGF-I concentration is significantly higher than other treatment groups(P < 0.05).The MT group of prolactin concentration significantly higher than that low protein and MTIL group prolactin concentration(P < 0.05).The LP group and the MTIL group had a significantly higher than M and MT group in 4EBP1 mRNA express.MTIL group had a significantly higher than M group in mTOR express.MT group had a significantly lower than high protein,low protein and MTIL group in the phosphorylation of S6K1.Compared with HP and MTIL group,LP and M had significantly in phosphorylation of 4EBP1(P < 0.01).HP group was significantly lower than add AA three groups in phosphorylation of 4EBP1(P < 0.05).Conclusion: Supplying the Met,Ile and Leu can increase the milk yield.Increasing the protein level increases milk production by increasing DMI.The addition of rumen AA will increase the yield of milk protein and increase the content of urea in plasma.The phosphorylation of AKT is not only affected by insulin,but also other influencing factors.The addition of Leu and Ile will affect the phosphorylation of mTOR in mammary tissue. |
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