Intra‐ and Inter‐Day Variability in Plasma Bicarbonate Concentration in Sedentary Horses

Abstract

IntroductionAlkalinizing agents have been given to horses before exercise to provide exogenous buffering effects. The objective of this experiment was to determine the intra‐ and inter‐day variability of resting plasma tCO2. The hypothesis was that tCO2 would vary measurably during a multi‐day quarantine.MethodsEight acclimated sedentary horses had jugular venous samples collected into 10‐ml heparinized evacuated glass tubes 3 times daily (7 AM, 11 AM, and 3 PM) for 5 consecutive days. Horses ate 5.3 kg alfalfa hay at both 7 AM and 3 PM after blood sampling. Plasma tCO2 was determined within 1–3 hours of sampling using an automated chemistry analyzer. Mean tCO2 for all 8 horses was calculated for each of the 15 sampling intervals. Results were compared by Repeated Measures ANOVA. When there was no apparent day‐to‐day effect, data for all horses were pooled by time‐of‐day (n = 40 samples for each of 3 times‐of‐day) and compared by the Student's t test to determine time‐of‐day effect. P<0.05 was considered significant.ResultsMean tCO2 over the 15 sampling intervals ranged from 28.9‐to‐31.6 mmol/L and was lower at 11 AM (Day 1) and 3 PM (Days 1, 3, and 4) compared to 7 AM on Day 1 (P<0.05). Individual plasma tCO2 ranged over 4‐to‐7 units (low 26, high 34, widest range 26–32, narrowest 28–31). Mean pooled tCO2 differed by time‐of‐day, with 11 AM (30.1 ± 0.2, P = 0.011) and 3 PM (29.8 ± 0.2, P<0.001) values lower than 7 AM values (31.0 ± 0.2).ConclusionsPlasma tCO2 differed significantly by time‐of‐day with considerable intra‐ and inter‐individual variability.Ethical Animal ResearchThe study was approved by the University of Illinois Institutional Animal Care and Use Committee. Sources of funding: Fédération Equestre Internationale and Maria Caleel Fund for Equine Sports Medicine Research. Support for Dr. Bergstrom was provided by the Merial Veterinary Scholars Program. Competing interests: none.