Nonruminant Nutrition: Vitamins and Management

The deposition of dietary supplemented folic acid (FA) into the chicken egg is likely regulated by its absorption in the intestine. Therefore, factors affecting the intestinal transport of FA in the laying hen may influence the level of egg folate concentrations. To this end, a series of experiments using intestinal everted sacs were conducted to characterize the different aspects of the intestinal FA absorption process in laying hens. Effects of naturally occurring folate derivatives (5-methyl and 10-formyltetrahydrofolate) on FA absorption were also investigated. Folic acid absorption was measured based on the rate of uptake of 3H-labeled FA in the everted sac from various segments of the small and large intestines. Folic acid concentration, incubation length, and pH condition were set to optimum before the performance of the uptake experiments. The distribution profile of FA transport along the intestine was highest in the upper half of the small intestine. Maximum uptake rate (nmol•100 g tissue-1•min-1) was observed in the jejunum (22.3 ± 2.0) and duodenum (20.6 ± 1.9) and decreased significantly (P < 0.001) in the ileum (15.3 ± 1.1) and cecum (9.3 ± 0.9). Transport characteristic of FA in the jejunum demonstrated a pattern of saturation, exhibiting decreased uptake rate with increased FA concentration. Transport increased proportionately (P < 0.002) between 0.0001 and 0.1 μM FA but showed a trend toward saturation in excess of 0.1 μM FA. Folic acid uptake in the jejunum showed greater transport at lower pH, exhibiting highest uptake at pH 5.5–6.0 but decreased (P < 0.009) at higher pH (7.5). Presence of 5-methyl and 10-formyltetrahydrofolate impeded FA uptake, reducing intestinal FA absorption by 21.9 and 14.9%, respectively, when added at concentrations ranging from 0 to 100 μM. Overall, these data indicated the presence of a FA transport system in the entire intestine of the laying hen. Uptake of FA in the cecum raises the likelihood of absorption of bacterial-derived folate.