Abstract
BackgroundThe 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).ResultsIn 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 of αS2-casein and α-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.ConclusionsOur 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.
Highlights
The local supply of energy-yielding nutrients such as glucose seems to affect the synthesis of milk components in the mammary gland (MG)
There were two reasons to provide animals with 81% of the energy requirements only: 1) the locally available MG glucose supply (LMGS) should have the largest effects on mammary amino acid (AA) sensing and utilization and milk protein synthesis under conditions of energy shortage, and 2) in Chinese dairy goat farms, energy shortage is generally considered common so the experiment was likely to be representative of the natural feeding conditions
Increasing the LMGS changed the total AA in milk in a quadratic manner (P-quadratic = 0.02), where they increased with infusions of 0 to
Summary
The local supply of energy-yielding nutrients such as glucose seems to affect the synthesis of milk components in the mammary gland (MG). 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.). Local nutrition, being an important part of precision nutrition, relates to nutrient supply, uptake and utilization in a specific organ, tissue or cell [1]. The functional mammary gland (MG) serves as a lactating organ and its nutrition is of high importance. The mTOR pathway has been shown to be critical for AA sensing and utilization in the lactating bovine or mouse MG [9, 10]
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