Plasma ascorbic acid, antioxidant capacity, and reactive oxygen species in healthy foals

OBJECTIVE To describe ascorbic acid (AA) concentrations, plasma antioxidant capacity (PAC) and markers of oxidative stress, as measured by derivatives of reactive oxygen metabolites (dROMs), in healthy foals at birth and during the first month of life. SAMPLES Venous blood samples were collected from healthy Standardbred (n = 13) and Quarter Horse (n = 10) foals. Plasma AA, PAC, and dROMs were assessed at 3 to 12 hours, 3 days, and 1, 2, and 4 weeks of age. PROCEDURES AA was measured via high-performance liquid chromatography. PAC and dROMs were measured with a free radical analytical system. Comparisons of AA, PAC, and dROMs at different time points were assessed. RESULTS Mean ± standard deviation AA concentrations at 3 to 12 hours (44.7 ± 19.6 μmol/L; P ≤ .01), 1 (48.6 ± 22.5 μmol/L; P ≤ .001), and 2 weeks (41.8 ± 15.8 μmol/L; P ≤ .001) were higher than at 4 weeks of age (28.5 ± 12.7 μmol/L). Both PAC and dROMs significantly increased at different time points compared to 3 to 12 hours of age. CLINICAL RELEVANCE Healthy foals have higher plasma AA concentrations shortly after birth, which then gradually decrease throughout the first month of life, suggesting that AA may represent a key antioxidant in the postnatal period. The concurrent increase in PAC and dROMs suggests that dynamic development of oxidative balance occurs after birth in foals. Development of AA, PAC, and dROM reference ranges in healthy foals could be used to guide therapeutic interven-tions and monitor during disease states characterized by increased oxidative stress.