Circadian changes in blood ionized calcium, sodium, potassium, and chloride concentrations and pH in cattle.

OBJECTIVE

To explore diurnal variation in blood ionized calcium, sodium, potassium, and chloride concentrations and pH in pregnant dairy cows.

ANIMALS

14 dairy cows in their third or later pregnancy approximately 6 weeks before expected parturition.

PROCEDURE

Throughout a 24-hour period, blood samples were taken at 2-hour intervals and analyzed for ionized calcium (iCa2+), potassium (K+), sodium (Na+), and chloride (Cl-) concentrations and pH. Paired t-tests were used to compare initial and final values. Circadian changes were tested by use of repeated-measures ANOVA. Additionally, a nonparametric analysis was performed for each animal to determine minimal and maximal values for the variables.

RESULTS

Significant differences were not detected between initial and final values of any variable. Repeated-measures ANOVA indicated significant diurnal fluctuations in all variables. With the exception of Cl- concentration, nonparametric analysis of individual values also revealed significant changes over time.

CONCLUSIONS AND CLINICAL RELEVANCE

The magnitude of daily fluctuations does not make it necessary to standardize time of sample collection for routine diagnostic examination of blood iCa2+, Na+, and Cl-concentrations and pH. However, it may be important to standardize time of sample collection in comparative studies in which more discrete differences may be identified.