Proteomic characterization of whey from colostrum, transitional milk, and mature milk of Murciano-Granadina goats, and valorization of transitional milk as an alternative for neonatal rearing

This study aimed to characterize the whey proteome of colostrum, transitional milk, and mature milk from Murciano-Granadina goats and to evaluate the use of transitional milk as a substitute for colostrum in feeding neonatal kids. Colostrum was collected at the first postpartum milking (within the first 12 h postkidding), transitional milk at the second postpartum milking (24 h after kidding), and mature milk at 3 to 4 mo postpartum. Proteomic analysis identified a total of 1,385 proteins, with 736 in colostrum, 668 in transitional milk, and 625 in mature milk. Colostrum and transitional milk displayed a high degree of similarity, particularly in proteins related to immune response and inflammation. In contrast, mature milk showed a shift toward proteins involved in metabolic and transport functions. To evaluate the practical application of transitional milk, newborn goat kids were fed either frozen colostrum (following standard farm protocol), freeze-dried colostrum, or freeze-dried transitional milk. All feeding strategies were well tolerated, with no adverse health effects, and resulted in similar growth performance. At 48 h of life, serum IgG concentrations were 13.95 mg/mL in kids fed frozen colostrum, 17.36 mg/mL in those fed freeze-dried colostrum, and 11.65 mg/mL in those fed freeze-dried transitional milk. Notably, kids fed freeze-dried transitional milk achieved satisfactory Ig levels, supporting its potential for passive immune transfer. These results highlight the biological value of transitional milk and support its use as a colostrum substitute in intensive farming systems, particularly when maternal colostrum is unavailable or insufficient. Furthermore, freeze-drying effectively preserved its functional properties, enabling convenient storage, handling, and administration. Overall, the successful use and preservation of transitional milk represent a sustainable approach to improving colostrum management, reducing waste, and increasing the efficiency of kid rearing in dairy goat production, in line with circular economy principles.