A Comparative Study on Immunoglobulin G Levels and Microbial Quality of Fresh and Freeze-Dried Bovine Colostrum

Ensuring adequate passive transfer of immunity in neonatal calves primarily depends on the immunoglobulin G (IgG) content and hygienic quality of colostrum. Various preservation methods have been used to maintain IgG concentration and control bacterial growth, and among these, freeze-drying has emerged as a promising and innovative approach. This study aimed to compare IgG concentrations and microbiological quality of fresh colostrum and freeze-dried colostrum powder. Colostrum samples (n = 28) with Brix values ≥27% were collected from tuberculosis- and brucellosis-free dairy herds. Each sample was divided into fresh and freeze-dried aliquots. IgG concentrations were measured using a bovine-specific quantitative ELISA kit, and total bacterial counts were determined by standard culture methods. IgG concentrations were 84.45 ± 2.35 mg/mL in fresh colostrum and 72.62 ± 1.59 mg/mL in freeze-dried samples, representing approximately a 14% reduction (p < 0.001). Despite this decrease, IgG levels remained above the minimum threshold required for successful passive transfer. Total bacterial counts decreased significantly from 1.78 × 10⁵ ± 1.70 × 10⁴ to 1.63 × 10⁴ ± 6.54 × 10³ cfu/mL, corresponding to a 90.9% reduction (p < 0.001). Escherichia coli, coagulase-negative Staphylococcus spp., Bacillus spp., and Candida spp. were isolated in both forms, while Staphylococcus aureus was detected only in fresh colostrum and not after freeze-drying. These results demonstrate that freeze-drying markedly enhances microbiological safety while preserving IgG concentrations at functionally adequate levels, supporting its use when fresh high-quality colostrum is unavailable or where pathogen transmission risk is a concern. Future studies should evaluate long-term storage conditions to better define the stability of IgG and microbial dynamics over time.