This study investigated the effects of lactational feed supplementation with yeast, arginine, selenium, and vitamin E on the colostrum and milk composition of primiparous DanBred sows. Colostrum composition changed markedly within the first 24 hours after farrowing, with total protein and immunoglobulin concentrations decreasing and lactose increasing, reflecting the physiological transition from immunity transfer to milk production. Arginine and antioxidant supplementation stabilized nutrient and antibody levels, suggesting improved mammary blood flow and oxidative balance, whereas yeast had only minor effects. These dietary interventions influenced colostrum stability but did not alter the natural progression toward mature milk. The results confirm that appropriate maternal nutrition during late gestation can enhance colostrum quality, passive immunity transfer, and early-life performance of piglets.