Bioscientifica Proceedings

Among livestock species, swine exhibit the most severe naturally-occurring intra-uterine growth restriction (IUGR) primarily due to a reduction in net protein synthesis. Thus, new knowledge about fetal metabolism of amino acids (AA), which are building blocks for proteins and regulators of intracellular protein turnover, can provide a solution to this problem. Among all AA, requirements of glutamate and glutamine by fetal pigs are quantitatively the highest, but cannot be met through uterine uptake alone. Nearly all glutamate and ~70% glutamine in diets for gestating swine are degraded in the maternal small intestine and, therefore, do not enter the portal circulation. This necessitates interorgan AA metabolism involving maternal skeletal muscle, placenta, and fetal skeletal muscle to synthesize glutamate and glutamine from branched-chain AA, as well as storage of glutamate and glutamine in allantoic and amniotic fluids. The porcine placenta does not degrade arginine or glutamine, leading to their maximal transfer from maternal to fetal blood. Therefore, maternal sources of ornithine and proline play a major role in the placental synthesis of polyamines needed for placental growth including placental vascular growth. Likewise, during late gestation, uterine uptake of arginine, proline and aspartate/asparagine cannot meet requirements for optimal fetal growth. To provide sufficient arginine, the fetal small intestine synthesizes citrulline and arginine from glutamate and glutamine, and fetal kidneys convert citrulline into arginine. Collectively, glutamine and arginine are major sources of AA nitrogen transferred between mother and fetus. Results of recent studies indicate that dietary supplementation with these two AA can ameliorate IUGR in swine. These findings greatly advance the field of maternal-fetal AA metabolism in pigs, but also have important implications for improving reproductive efficiency in swine production worldwide.

© 2013 Context Products Ltd