Protein, Antioxidant, Oxidant and Enzymatic Markers in Colostrum and Milk of Spanish Purebred Mares.

Despite the recognized biochemical complexity of mare colostrum and milk, longitudinal characterization of whey proteins, oxidant-antioxidant balance and enzyme activities across lactation remains limited. This study evaluated total whey proteins (TWP), albumin (ALB), globulins, immunoglobulin G (IgG), oxidative and antioxidant markers, and enzymatic activities in colostrum and milk from 29 clinically healthy Spanish Purebred mares during the first 120 days postpartum. TWP and ALB were quantified using validated spectrophotometric assays, and IgG were measured by immunoturbidimetry. Antioxidant capacity was assessed using Trolox equivalent antioxidant capacity, cupric reducing antioxidant capacity (CUPRAC), and ferric reducing antioxidant power (FRAP), together with determination of uric acid (UA). Oxidative status was evaluated by total oxidant status and advanced oxidation protein products, and alkaline phosphatase and gamma-glutamyl transferase activities were measured using IFCC‑standardised methods. In early lactation, serum-derived proteins, UA, oxidant markers and enzymatic activities reached their highest values, reflecting the intense metabolic and immunological activity of the immediate postpartum period. In contrast, CUPRAC and FRAP increased progressively throughout lactation, consistent with mammary maturation and the establishment of a more stable antioxidant environment in mature milk. In conclusion, mare colostrum and milk undergo a coordinated biochemical transition from an immunologically enriched and oxidatively active colostrum to a more stable mature-milk profile.