Effect of frozen storage of bovine colostrum for up to 1 year on concentrations of immunoglobulins and insulin as well as bacterial counts.

Freezing colostrum is a common management strategy to ensure availability of high-quality colostrum for each calf. Limited data are available on the effects of freezing colostrum on important colostral components. The objective of this study was to investigate the effects of freezing bovine colostrum at -20°C for 1 yr on concentrations of IgG, IgA, IgM, and insulin, as well as on total plate count (TPC) and coliform counts (TCC). Composite colostrum samples (250 mL) were collected from the complete first milking from Holstein cows (n = 10), immediately cooled on ice, and divided into fourteen 8-mL aliquots. One aliquot was stored on ice for analysis within 6 h of collection (fresh) and 13 additional aliquots were frozen and stored at -20°C for subsequent analyses upon thawing at 21°C to 24°C in 4-wk intervals. All samples were analyzed for Brix % via a digital Brix refractometer; IgG, IgA, and IgM via radial immunodiffusion; insulin via radio immunoassay; and TPC and TCC via commercial ready-to-use aerobic bacterial culture plates. Data were analyzed using mixed effects repeated-measures ANOVA. Compared with fresh colostrum, Brix % was 4.1% ± 0.9% to 6.2% ± 0.9% lower between 4 and 52 wk. Concentration of IgG was reduced 8.1% ± 2.8%, 7.6% ± 2.5%, and 8.2% ± 2.3% at 32, 44, and 48 wk relative to sampling, respectively. Freezing colostrum did not affect concentrations of IgA or IgM. Insulin concentrations were reduced 14.5% ± 3.5% at 16 wk, 11.1% ± 3.0% at 40 wk, 18.4% ± 3.3% at 48 wk, and 20.8% ± 3.2% at 52 wk relative to sampling compared with insulin concentration determined in fresh colostrum. Coliform count was reduced 22.1% ± 7.6% by 4 wk and continued to be lower at each time point through 52 wk. Total plate count was reduced at 4, 20, and 24 wk to 46.9% (30.9%-71.4%), 47.9% (31.5%-72.9%), and 51.0% (33.3%-78.1%) of the TPC in the fresh colostrum, but did not differ at the other time points. We conclude that freezing colostrum appeared to affect Brix %, TCC, and concentrations of IgG and insulin. As such, producers should store colostrum at -20°C for no longer than 32 wk to minimize the risk of a change in the composition.