AMPK-mTOR pathway is involved in glucose-modulated amino acid sensing and utilization in the mammary glands of lactating goats

Background:The local supply of energy-yielding nutrients such as glucose seems to affect the synthesis of milk components in the mammary gland(MG).Thus,our study was conducted to investigate the effects of locally available MG glucose supply(LMGS)on amino acid(AA)sensing and utilization in the MG of lactating dairy goats.Six dosages of glucose(0,20,40,60,80,and 100 g/d)were infused into the MG through the external pudendal artery to investigate the dose-dependent changes in mammary AA uptake and utilization(Exp.1)and the changes in mRNA and protein expression of the AMPK-mTOR pathway(Expt.2).Results:In Exp.1,total milk AA concentration was highest when goats were infused with 60 g/d glucose,but lower when goats were infused with 0 and 100 g/d glucose.Increasing LMGS quadratically changed the percentages ofαS2-casein andα-lactalbumin in milk protein,which increased with infusions from 0 to 60 g/d glucose and then decreased with infusions between 60 and 100 g/d glucose.The LMGS changed the AA availability and intramammary gland AA utilization,as reflected by the mammary AA flux indexes.In Exp.2,the mRNA expression of LALBA in the MG increased quadratically with increasing LMGS,with the highest expression at dose of 60 g/d glucose.A high glucose dosage(100 g/d)activated the general control nonderepressible 2 kinase,an intracellular sensor of AA status,resulting in a reduced total milk AA concentration.Conclusions:Our new findings suggest that the lactating MG in dairy goats may be affected by LMGS through regulation of the AA sensory pathway,AA utilization and protein synthesis,all being driven by the AMPK-mTOR pathway.

Effects of infusing milk precursors into the artery on rumen fermentation in lactating cows

This experiment was conducted to investigate the effects of infusing milk precursors into the external pudic artery on rumen fermentation in lactating dairy cows. Eight multiparous Holstein cows were randomly assigned to Group A(experimental group) and Group B(control group) with 4 cows each. A2×4 complex factor crossover design was used. Cows in Group A were fed corn straw as the only roughage, and cows in Group B were fed mixed roughage. The experiment was divided into two periods.In the first period, cows in Group A, received treatments: 1) a basal infusate as a control(CSC); 2) a milk fat precursor infusion including C16:0, C18:0, C18:1 c9, C18:2 c6, C18:3 n3, acetic acid(CSF); 3) a milk protein precursor infusion including 16 amino acids(CSA); 4) the mixed infusion of milk fat and protein precursors(CSFA). And meanwhile, cows in Group B were infused the basal infusate as a control group. In the second period, the cows in both Groups A and B were crossed over, which cows in Group A were named as Group B and the cows originally in Group B were in Group A. The experimental results showed that cows in experimental group had higher ruminal pH compared with the control, and ruminal pH in CSC, CSF, CSA were significantly higher than those in their respective control group(P < 0.05). The concentration of ammonia nitrogen(NH_3-N) was significantly higher in CSA and CSFA compared with Group B(P < 0.05). We also observed that the infusion of mixed amino acids significantly increased the bacterial protein(BCP) content in rumen(P < 0.05) and influenced the rumen acetic acid concentration as well as the acetic to propionic ratio(P < 0.05). Milk fat precursors infusion significantly affected butyric acid concentration(P < 0.05). In addition, the content of lipopolysaccharide(LPS) in CSA was significantly higher than that in the control group(P < 0.05). It is concluded that the milk precursors infused into external pudic artery caused feedback effects on ruminal fermentation under the corn straw roughage conditions. The milk protein precursor increased the ruminal pH, the contents of BCP and acetic acid, which adjust rumen fermentation and improve milk performance.