Alteration of plasma folates in gestating sows and newborn piglets.

Plasma folates tetrahydrofolate (THF) and N5-methyltetrahydrofolate (5MF) were determined in nongestating, gestating, and lactating sows (2 to 4 yr old, 2-6 parities, n = 88) and in newborn, growing, and finishing pigs (0 to 158 days old, n = 191) with the use of high-performance liquid chromatography with an electrochemical detector. Plasma folates after folic acid injection (1 mg/kg iv) were also monitored in 2-day-, 2-wk-, and 2-mo-old pigs. In sows, plasma folates decreased significantly as pregnancy advanced. This was mainly due to the decrease of THF, which must be caused by the folate supply from the maternal body to the fetuses. In newborn piglets, levels of "total" plasma folates were much higher than those in adults (nongestating sows), and 5MF was the major folate content. This result may be related to the observation that, after folic acid injection, newborn piglets showed much higher metabolic activity of folic acid to 5MF than adults. Rapid and drastic decrease of plasma folate was observed during nursing in piglets, which is considered to be associated with the decrease of the metabolic activity of folic acid and rapid expansion of body volume together with negative folate intake during the nursing period.