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Colostrum is the initial secretion of the mammary gland produced by mammals shortly after parturition. Colostrum is rich in macro- and micronutrients, antimicrobial peptides, and growth factors1,2,3,4. The composition varies gradually over time through the transition to mature milk5,6,7 but most significantly within 24 h after parturition8. The composition of colostrum is also influenced by maternal factors, including age, parity, breed, health, and nutritional status, as well as extrinsic factors, including season, premature parturition, premature lactation, colostral handling factors (pooling colostrum and storage temperature), and induction of parturition9,10,11. Compared with mature milk, colostrum contains less lactose and more fat, protein, peptides, non-protein nitrogen, ash, hormones, growth factors, cytokines, nucleotides, vitamins, and minerals12. Bovine colostrum contains a wide range of proteins, including immunoglobulins, lactoferrin, α-lactalbumin (α-LA), β-lactoglobulin (β-Lg), lactoperoxidase, and several growth factors13. The total protein concentration of bovine colostrum ranges between 11.26 mg/mL and 169.55 mg/mL14. The protein content comprises whey and casein at an average concentration of 124.00 mg/mL and 26.00 mg/mL, respectively15. The whey portion contains three major types of immunoglobulins (Igs) as IgG (85%-90%), IgM (7%), and IgA (5%)16. The major Ig in bovine colostrum is IgG, which provides passive immunity and modulates the adaptive and innate immune systems in the calf17. The initial Ig concentration of the first milking bovine colostrum can range from 20 to 200 mg/mL and decrease to around 0.4-1.0 mg/mL18. The mean IgG concentration is approximately 60 mg/mL and declines steadily to the levels below 1 mg/mL throughout the transition to mature milk19.
Another important bioactive protein in colostrum is lactoferrin, an iron-binding glycoprotein with a concentration of 1.5-5 mg/mL. Properties of lactoferrin include enhancing iron absorption as well as possessing antimicrobial activity20,21, binding lipopolysaccharide, immune-modulation, and stimulating the growth of intestinal epithelial cells and fibroblasts22. Bovine colostrum also contains α-lactalbumin and β-lactoglobulin. These proteins are sources of essential amino acids and also have bactericidal activity23,24,25. The mean α-LA and β-Lg concentrations in colostrum average 2.77 mg/mL2, and 11.5 mg/mL26, respectively. Thereafter, these concentrations decrease to 1-1.5 mg/mL27, and 4.8 mg/mL26 in mature milk. Colostrum also contains a significant amount of lactoperoxidase (mean 22.8 µg/mL) and lysozyme (mean 0.40 µg/mL)26. Lactoperoxidase is a glycoprotein that possesses antimicrobial activity against Gram-positive and negative bacteria28 by producing reactive oxygen species. Lysozyme functions as an antimicrobial agent by cleaving the peptidoglycan component of bacterial cell walls, thereby leading to celldeath29,30.
Due to their properties, IgG and lactoferrin are processed into different food products to fortify infant formulas, food supplements, high-protein preparations for convalescents and sportsmen as well as in pharmacology and cosmetology31,32,33. Bovine colostrum represents an important source of IgG and lactoferrin. However, the composition of these bioactive proteins in bovine colostrum changes markedly during the lactation period. Therefore, monitoring changes in the concentration of these bioactive proteins in colostrum samples used for research and food processing is critical. This study aims to describe the methods for monitoring the concentration and compositions of the total protein, lactoferrin, and IgG in bovine colostrum during the 6 days after calving.