Enrichment of eggs with folate is possible when dietary folic acid levels are increased. However, development of optimal strategies for the production of folate-enriched eggs requires knowledge as to differences due to strain of bird and a greater understanding of the factors limiting egg folate deposition. To this end, a study was designed to determine the response of two leghorn strains that differ in production performance. Hyline W36 and W98 hens (n = 6 per diet) received a barley-based ration containing 0, 2, 4, 8, 16, 32, 64, or 128 mg/kg of crystalline folic acid for 21 d. Response criteria included production parameters, measures of blood folate status, and egg folate content. Significant (P < 0.05) main effects of folate supplementation were observed for egg folate content and plasma folate, which increased, and homocysteine concentrations, which decreased with supplementation; performance, however, was not affected. The Hyline W98 strain had significantly (P < 0.05) higher total egg and yolk weights and feed consumption when compared with the W36. Significant (P < 0.05) ration x strain interactions were observed for egg and yolk weight, egg folate content, and plasma homocysteine. The higher egg mass producing strain, Hyline W98, benefited from increased folic acid through a reduction in plasma homocysteine concentrations, suggesting that this strain has a higher requirement for folate than the W36 strain. Overall, egg folate content is maximized when crystalline folic acid is supplemented to the diet at 2 mg/kg or higher. Higher levels of egg folate are not achieved due to the saturation of the precursor pool for egg folate deposition.

Supplementing laying hen diets with folic acid at 4 mg/kg of diet for 3 wk led to the production of folate-enriched eggs with an approximately 3-fold increase in egg folate concentration relative to a regular commercial egg. However, because long-term consistency in folate deposition is important for successful folate enrichment of natural foods such as eggs, 2 studies were designed to determine the level of folic acid required to maximize egg folate content and consistency throughout the entire cycle of egg production. In study 1, Hy-Line W36 and W98 laying hens (n = 156/treatment) received a barley-based diet containing 0 and 4 mg/kg of folic acid, whereas in study 2, a total of 1,248 Hy-Line CV20 laying hens (n = 416/treatment) received a barley-based ration supplemented with folic acid at 0, 2, or 4 mg/kg of diet. Both studies lasted for eleven 28-d periods. Response criteria included production parameters, egg quality measurements, and measures of egg folate content. Results of both long-term production studies support the use of 4 mg of folic acid/kg of diet as the recommended level of folic acid supplementation in terms of maximizing egg folate concentration over time. This is supported by the higher egg folate content and more consistent egg folate deposition at 4 mg of folic acid/kg of diet as compared with 0 and 2 mg of folic acid/kg of diet. Hy-Line W98, a strain of hens selected for large egg mass, benefited more from increased dietary folic acid in terms of increased egg production than did Hy-Line W36 and CV20 hens, strains selected for better egg efficiency and livability. Sensitivity and responsiveness to increasing dietary folic acid concentration in terms of egg folate content were, however, similar for all strains. In conclusion, eggs of laying hens were consistently enriched with folate by dietary supplementation with 4 mg of folic acid/kg of diet throughout the production cycle.

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