PSIII-6 Effects of repeated freeze and thaw cycles on serum and plasma metabolite concentrations in beef cattle

The objective of this study was to determine whether repeated freeze and thaw cycles alter bovine circulating metabolite concentrations, which serve as indicators of nutrient utilization. In research settings, it is common to thaw and refreeze samples when confirming results or performing further analyses; thus, it is important to determine if these actions alter metabolites. Jugular blood samples were collected from beef cows (n = 14) and fall-born calves (n = 14) at weaning. Samples were processed into multiple aliquots and stored at -20°C until analysis. Samples were thawed at 4°C for 8 to 10 h on each day of analysis and refrozen for at least 48 h between cycles. Concentrations of serum non-esterified fatty acids (NEFA), serum urea N, plasma triglycerides, and plasma glucose were analyzed using commercially available kits on a UV-visible light plate reader. Data were analyzed with sample type (cow vs. calf), thaw (cycles 1-4), and their interaction in a mixed model. Additionally, R2 were determined among freeze-thaw cycles within each metabolite. Thaw cycle impacted glucose concentrations (P = 0.03); other metabolites were unaffected (P > 0.25). Thaw cycle and its interaction with sample type did not affect metabolite concentrations (P > 0.33). Sample type did not affect triglyceride and BUN concentrations (P > 0.34). There was a type effect (P < 0.0001) for NEFA and glucose; NEFA were greater in cows and glucose was greater in calves. There was a strong relationship between urea N thaw cycles 1 and 2 (R2 = 0.88), which was also apparent between all other urea N, triglycerides, NEFA, and glucose cycles (R2 ≥ 0.79, 0.96, 0.91, and 0.61 respectively). These data indicate that repetitive freezing and thawing of bovine serum and plasma samples has little effect on non-esterified fatty acids, triglycerides, and urea N, but may impact glucose concentrations.