Eggs are a widely consumed and nutritionally valuable food, increasingly recognized for their potential to deliver not only essential nutrients but also health-promoting phytochemicals such as carotenoids and polyphenols. However, the presence and variability of these compounds in eggs remains poorly understood, particularly in pasture-raised systems where hens have access to fresh forage. This review explores the current state of knowledge regarding the transfer of phytochemicals from forage to eggs, highlighting the factors that influence their deposition and the implications for egg nutrient quality, hen health, and consumer health. Forage composition, which varies by plant species, season, and management practices, plays an important role in determining phytochemical intake of the hen, and consequently the egg content. While evidence suggests pasture access enhances yolk carotenoid levels and may contribute to polyphenol deposition, little is known about farm-to-farm variation and the degree of nutrient transfer. As pasture-based egg systems continue to gain popularity, understanding and optimizing phytochemical transfer from diet to egg could improve the consistency and nutritional value of eggs while supporting sustainable food production goals.

Regenerative, pasture-raised layer hen systems create synergistic relationships between the hens, forage, soil, and weather, fostering a sustainable system. However, the influence of these factors on egg nutrient profile and quality may vary by region. This study took place over two years; samples were collected from a farm in Ohio during the first year and a farm in Indiana during the second year. Egg (n = 12) and forage (n = 3) samples were collected monthly from September to December. Fatty acids were quantified using gas chromatography-mass spectrometry, micronutrients were assessed in a commercial laboratory, and carotenoids and polyphenols were analyzed colorimetrically. Ohio eggs had significantly darker yolks (average yolk fan score: 8.5 ± 1.8 vs. 3.9 ± 2.0; p < 0.0001), a higher beta carotene and carotenoid content, and a lower n-6:n-3 fatty acid ratio across the season. Indiana eggs had a lower average total phenolic content (0.07 ± 0.00 mg GAE/g vs. 0.14 ± 0.10 mg GAE/g) and lower average total cholesterol (5.35 ± 2.9 mg/g vs. 10.99 ± 1.54 mg/g). Forage composition and soil parameters varied between farms. Regional variations in forage composition, soil nutrients, and regional weather can significantly influence the nutrient density of eggs produced in sustainable, pasture-raising systems. This research highlights how local environmental factors can shape the nutritional profiles of eggs in different regions. Future studies should explore this relationship in more regions.