Restricted dietary chloride and sodium bicarbonate supplementation in early lactation Holstein cows: cerebrospinal fluid electrolyte alterations.

As part of an experiment designed to study the acute and chronic metabolic changes associated with dietary chloride (Cl) restriction and sodium bicarbonate (NaHCO3) supplementation in cows in early lactation, base-line and final experimental CSF specimens were collected to evaluate the relative effects of a nutritional Cl deficiency on serum and CSF electrolyte concentrations. Attention was paid to the comparative alterations in serum and CSF Cl concentrations as an indication of the potential for the choroid plexus active Cl transport mechanism to conserve CSF Cl concentrations in the face of total body Cl depletion. Serum Cl values in cows fed the restricted Cl diets decreased from 96.4 +/- 3.5 mEq/L to 83.4 +/- 4.5 mEq/L in a 2-week trial and from 106.0 +/- 2.8 mEq/L to 75.5 +/- 6.7 mEq/L in an 8-week trial, as an indication of a nutritional Cl deficiency. Healthy cows maintained CSF Cl concentrations approximately 20% higher than the serum values, whereas cows fed a diet containing 0.10% Cl and 0.70% NaHCO3 for 2 weeks maintained CSF Cl values at 134.8% of the serum Cl concentrations, and CSF Cl concentrations in cows given a diet with 0.10% Cl and 0.80% NaHCO3 for 8 weeks increased to 137.2% of the serum Cl values.