An estimation of the requirement for folic acid in gestating sows: The metabolic utilization of folates as a criterion of measurement

Sows at their second parity were randomly distributed in five groups of sev en animals each to determine the dietary concentration of folic acid that o ptimizes the metabolic utilization of the vitamin during gestation. The gro ups differed by dietary supplement of folic acid: 0, 5, 10, 15, or 20 ppm. Sows were fed 2.5 kg of diet each day. The response of serum folates and fo late binding capacity to treatments and the excretion of urinary folates af ter an i.v. injection of folic acid were measured. The total daily excretio n of urinary folates was corrected according to the response to one i.v. in jection of saline on the day preceding the i.v. injection of folic acid. Th e decrease of total serum folates throughout gestation was less pronounced in the groups fed 15 and 20 ppm of dietary folic acid (supplement x period interaction, P <.06) than it was in the other three treatments. The proport ion of i.v. folic acid not recovered in sow urine (injected - excreted) dec reased as the amount of dietary folic acid increased to reach a minimum, wh ich differed according to the period (supplement x period interaction, P <. 02); it was 15 ppm during wk 1 of gestation and 10 ppm for the other period s studied. The unrecovered folates increased over a dietary concentration o f 15 ppm. These minimum values correspond to the most appropriate feed conc entration that covered the whole body utilization (tissue and cell metaboli sm, catabolism, and storage) of folates by the sows and could be interprete d as a reliable index of the requirement.