Mothers can pass many traits to their offspring, including immunity. In chickens, nutrient supplementation of the hen can improve the immunity and growth of her chicks. However, the exact mechanisms of such maternal effects aren’t clear. To learn more, researchers recently examined the immune molecules in the reproductive tracts and eggs of hens. Compared with those of non-supplemented hens, eggs of supplemented hens had higher levels of antimicrobial peptides and antibodies in their whites and yolks. The supplemented hens also had higher levels of these molecules in the sections of their reproductive tracts that make those parts of the egg, confirming that they transferred the immune factors during egg formation. The researchers next examined intestinal development and gut microbes in offspring, since the intestinal microbiome is known to influence immunity. They found that maternal supplementation improved chick intestinal development beginning in the embryonic period by affecting the expression of development- and immunity-related genes in the embryonic gut and shaping the gut microbiome. Specifically, microbes were transferred from the mother’s reproductive tract to the embryonic gut via the egg white. Although experiments on mother–offspring pairs are needed, the findings shed light on the mechanisms of maternal effects and might help improve animal health and production.