Folic Acid Folate

A bacterial growth factor was found in spinach leaves that prevented anemia in chicks. This factor was isolated and identified as folic acid (pteroylmonoglutamic acid). The term folate is used as a generic descriptor for folic acid and related compounds exhibiting the biological activity of folic acid.[1,2]

Intestinal absorption of folates is thought to occur at the monoglutamate level. Hydrolysis of the polyglutamates to monoglutamates occurs within the brush border membrane of the small intestine. Intestinal transport of the monoglutamyl folates is carrier-mediated and pH-depen-dent. Folates are absorbed by a simple diffusion mechanism when concentrations are at pharmacological levels. Absorbed folates are taken up by the liver and converted back to polyglutamate derivatives, and either retained in the liver or released into the blood or bile.[2] The metabolic role of folic acid coenzymes in mammalian tissues is in the transfer of single carbon moieties. The coenzymatically active forms of folic acid are the tetrahydro derivatives. Specific reactions and enzymes in which these coenzymes are involved include methylation of homocysteine to methionine, the inter-

conversion of serine and glycine, the synthesis of purines and pyrimidines, and the oxidation of histidine and threonine.[1-3]

Most growing animals can obtain sufficient folic acid from feed ingredients and from bacterial synthesis in the intestine. However, reproducing animals may need more folic acid than supplied by feed ingredients. It has been demonstrated that in swine, serum folates decreased by 50% from weaning to day 60 of gestation.[4,5] The addition of 1 to 1.65 mg of folic acid/kg to a corn soybean meal diet resulted in an improvement in the total number of pigs born and born live over three parities.[6] Folic acid deficiency symptoms include a reduction in growth rate, fading hair color, macrocytic and normocytic anemia, leukopenial thrombopenia, reduced hematocrit, and bone marrow hyperplasia. It should be noted that a synthetic diet containing 1 to 2% of a sulfa drug or a folic acid antagonist was necessary to produce a folic acid deficiency. Folic acid is generally considered to be nontoxic, as no adverse effects have been reported following the ingestion of high levels of the vitamin in any of several species.[1]

Folates are supplied in the diet by most natural feedstuffs. However, the folate content of natural feed-stuffs is highly variable and therefore should be considered an unreliable source of the vitamin. The variability of folate content in feedstuffs may be due to variety, processing, and storage differences. Bacteria in the colon appear to produce a significant amount of folates, but the contribution of bacterial folates to the animals' needs is unknown and may be very low. The apparent digestibility of folates in feedstuffs appears to be variable. The apparent availability in wheat and barley is around 80%, while most protein meals have folate apparent availabilities in the 30 60% range.[1]

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