Objective: To determine the effect of IV administered hypertonic saline solution (HSS) on transruminal rehydration in clinically normal dairy cows.
Animals: 10 Holstein cows.
Procedure: Cows in a 2-way randomized cross-over design study were given nothing per os for 36 hours, then were randomly assigned to receive either an oral water load (OWL; 40 ml/kg of body weight) by ruminal gavage or HSS IV (5 ml/kg of body weight) plus OWL; 10 days later, each cow received the other treatment. Outcome measures included serum and urine osmolality, electrolyte (Ca, P, Na, K, and Cl), creatinine, blood glucose, hemoglobin (Hgb), and plasma total protein (PTP) concentrations; serum colloid osmotic pressure (SCOP); urine volume; PCV; and blood gas analytes (pH, P(CO2), P(O2), HCO3-, base excess [BE], and O2 saturation).
Results: IV administered HSS plus OWL caused Hgb, PCV, PTP, SCOP, blood pH, BE, HCO3-, and urine osmolality values to decrease and fractional excretion (FE) of electrolytes, serum osmolality, and urine volume to increase. Blood glucose concentration was different between treatments at 0 and 150 minutes, and FEK, FECl, and FECa were similar by 180 minutes after OWL alone, but absolute excretion of Na and P and FENa and FE(P) remained high after HSS administration. Oral water load caused Hgb, PCV, PTP, serum electrolyte and creatinine, SCOP, and urine osmolality values to remain unchanged or decrease slowly and pH, BE, HCO3-, FECa values to increase slightly by 180 minutes.
Conclusions and clinical relevance: IV administration of HSS plus OWL, unlike OWL alone, increases circulatory volume rapidly, induces slight metabolic acidosis, increases renal perfusion and glomerular filtration rate, and effects changes in serum Ca and P homeostasis that may be useful in treating sick dairy cows.