Abstract
This experiment was conducted to investigate the characteristics of folic acid (FA) absorption in laying hens and the effect of FA supplementation on cecal microbiota. A total of 432 healthy hens (30-week-old) were randomly assigned to four diets supplemented with FA: 0, 1, 6, and 24 mg/kg of feed for 8 w. Blood, duodenum, jejunum, ileum, cecum, and cecal chyme samples (six samples per treatment) were collected from the hens at the end of the feeding trial. Expression profiles of folate transport and transformation genes in intestine and cecal microbiota were detected. Results showed that serum folate level significantly increased (P < 0.01) with an increase in dietary FA supplementation, reaching a plateau at 6 mg/kg FA supplementation. The expression of FA transport and transformation genes was not affected in the cecum (P > 0.05) by dietary FA supplementation; however, it was affected in the duodenum, jejunum, and ileum and mostly showed a downward trend in treatment groups (P < 0.05). The genes affected include duodenal folate receptor (Folr) and dihydrofolate reductase (Dhfr), jejunal proton-coupled folate transporter (Pcft) and reduced folate carrier (Rfc), and ileal ATP binding cassette subfamily C member (Abcc2), Abcc3, Rfc, Folr, and Dhfr. Furthermore, according to the operational taxonomic unit classification and taxonomic position identification, the cecal microbiota population of the hens was not affected by dietary FA supplementation at the phylum, class, order, family, genus, and species levels (P > 0.05). However, the relative abundance of some microbiota was affected by dietary FA supplementation (P < 0.05). In conclusion, FA transport from the intestinal lumen into enterocytes, and then into the bloodstream, is strictly regulated, which may be associated with the regulation of the expression profiles of genes involved in FA absorption. Pathogenic bacteria decreased in the cecum, especially at 24 mg/kg supplementation, but the beneficial bacteria (Bifidobacteriaceae) decreased at this level, too. Overall, FA supplementation at 6 mg/kg, which was selected for folate-enriched egg production, did not affect the health and metabolism of laying hens negatively.
Highlights
The term folate refers to a group of compounds belonging to the water-soluble vitamins, playing an important role in one-carbon metabolism [1]
Serum folate and homocysteine levels were measured to determine the effect of dietary folic acid (FA) supplementation on folate metabolism in hens
reduced folate carrier (Rfc), and folate receptor (Folr) are relevant in FA absorption from the intestinal lumen into enterocytes
Summary
The term folate (vitamin B9) refers to a group of compounds belonging to the water-soluble vitamins, playing an important role in one-carbon metabolism [1]. People have gradually realized folate’s importance and have started looking for ways to supplement folate. Humans and animals lack the enzymes to synthesize folate de novo, so they must obtain it from their food. Yeast, animal livers, egg yolk, folic acid (FA)-fortified foods, or additives are all good folate sources for humans [7, 8]. Because of folate’s instability in vegetable sources [9, 10], the potential negative effects of synthetic FA [11,12,13], egg yolk folate draws considerable attention thanks to its stability, natural occurrence, and high bioavailability [14, 15]. Studies have shown that folate content in egg yolk can be increased by supplementing laying hen feed with FA. Intestinal absorption of FA is believed to be one of the main factors affecting the transfer of dietary FA into the egg
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