Effects of various concentrations and volumes of potassium sorbate on colostrum bacterial contamination over time at ambient and refrigeration temperatures

Preservation and storage of colostrum on farm is challenging, as cold temperature storage facilities (refrigerators and freezers) often cannot accommodate the volume of colostrum required to feed calves. Potassium sorbate preservative (PSP) is a readily available food-grade preservative used in wine and cheese production, shown to be very effective at preserving colostrum at both refrigeration and ambient temperatures. Aims of the current work were to determine the optimal concentration and inclusion volume rate (IVR) of PSP to preserve bovine colostrum for feeding to neonatal calves. Twenty individual cow point-of-feeding colostrum samples were collected and frozen at -20°C for 4 to 6 wk before testing (purposively selected). Three PSP concentrations were created (25.4%, 32.2%, and 39.1%) by mixing potassium sorbate crystals with 100 mL of distilled water. For each of these concentrations, either 50 µL (1% by volume) or 25 µL (0.5% by volume) were added to each 5-mL aliquot of colostrum to create 2 different IVR. For each concentration and IVR, one aliquot was stored at ambient temperature (AT; temperature monitored in the laboratory between 23.1°C and 24.6°C) and one aliquot was refrigerated (refrigeration temperature [RF]; temperature monitored in refrigerators between 3.1°C and 4.2°C). Baseline bacteria counts were also measured for each colostrum sample. Aliquots were tested for degree of bacterial contamination at 24, 72, and 168 h. Mixed linear regression models were constructed using total coliform count (TCC) and total bacteria count (TBC) as outcomes of interest, with concentration of potassium sorbate in distilled water (30 g/100 mL, 40 g/100 mL, or 50 g/100 mL), IVR (1% inclusion volume and 0.5% inclusion volume) and temperature (RF = 3.1°C-4.2°C or AT = 23.1°C-24.6°C) as predictors of interest. Survival analysis (with sample as a random effect term) was also used to account for bacteria counts too numerous to count (TNTC, assigned as 10,000,000 cfu/mL for TBC and 11,000 cfu/mL for TCC as these exceeded the highest measures). Bacteria TNTC was analyzed as a "failure event" and the time frame at which these failures occurred was analyzed. There was a significant temperature by IVR interaction for the TCC outcome. The RF conditions were more effective than AT in preventing bacterial proliferation at 24 and 72 h. Survival models showed a lower hazard of high contamination at IVR of 1% and concentration of 50 g/100 mL. In all cases, 50 g/100 mL concentration was more effective than concentrations of 30 g/100 mL and 40 g/100 mL or no preservative, and 1% IVR was more effective than 0.5% IVR or no preservative at preventing bacterial proliferation at 24 and 72 h. A large number of samples in this work were initially contaminated with total bacterial species and this may have biased results; however, this is representative of the current situation on most dairy farms.