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Oxidation of serum proteins leads to non-reversible carbonyl formation which alters their function and is associated with stress-related disease processes. The primary objective of this study was to quantify and identify oxidized serum proteins in fetal and newborn piglets. Protein carbonyls were converted to hydrazones with dinitrophenyl hydrazine and quantified spectrophotometrically. For identification, serum protein carbonyls were derivatized with biotin hydrazide, separated by 2D PAGE and stained with FITCavidin. Biotin-labeled proteins were excised from gels and identified by mass spectrometry. At birth, carbonyls were determined to be ∼600 pmole/mg serum protein. Fetuses at 50 and 100 days of gestation had similar levels of protein carbonyls as newborns. Carbonyl levels were also similar for control and runt (<1 kg at birth) piglets between 1 and 21 days of age; however, distribution of many proteins varied by age and was also influenced by birth weight. Major oxidized proteins identified in fetal (f) and newborn (n) pigs included; albumin (f, n), transferrin (f, n), fetuin-A (f, n) alpha fetoprotein (f, n), plasminogen (f, n), fetuin-B (f), alpha-1-antitrypsin (f, n) alpha-1-acid glycoprotein (f) and immunoglobulins (n). While abundance and distribution of oxidized proteins changed over time, these changes appear to primarily reflect relative amounts of those proteins in serum.