Changes in glutamine metabolism indicate a mild catabolic state in the transition mare.

This research study investigates how glutamine metabolism in mares changes during the transition period from late pregnancy through parturition (birth) and into early lactation. It reveals that lactation presents a mild catabolic state where decreased glutamine levels may affect other tissues like the intestines and immune system.

Research Context

• Glutamine is the most prevalent free amino acid in the mammalian body, significantly absorbed by the fetus during pregnancy and the mammary gland during lactation periods.
• The transition period, a phase involving late pregnancy, birth, and early lactation, is theorized to greatly affect glutamine metabolism in mares.
• Eight foals born to standardbred mares that received energy and protein 10% above the National Research Council (NRC) recommendations were the central focus of this study. The foals stayed with their mothers for six months.

Research Observations

• During lactation, the mares’ lean body mass reduced by 1.5% while the fat mass remained unchanged throughout the gestation and lactation periods.
• There was a substantial increase in the concentration of most plasma metabolites and hormones postpartum which was partly due to increased hemoconcentration from fluid shifts at parturition.
• The plasma concentration of glutamine was maintained at higher levels up to 2 weeks postpartum, but started to decrease afterwards, hitting the lowest point around the 6th week of lactation.
• Glutamine content in skeletal muscle stayed constant, but glutamine synthetase expression decreased at the end of the lactation period.

Research Findings

• Glutamine was found in high abundance in milk in early lactation. However, its concentration reduced by over 50% after 3 months of lactation, which paralleled the decrease in the plasma glutamine concentration.
• This data suggests that lactation denotes a mild catabolic state for the mare, with declining glutamine levels that may negatively impact other tissues such as the intestines and immune system.