Diagnosing Downer Cow Electrolyte Imbalance

Adapted by Dr. Pat Blanchard, California Animal Health and Food Safety Laboratory

The diagnosis of electrolyte imbalances (calcium, phosphorous, potassium and magnesium) in downer dairy cows often presents challenges.  Treatment with electrolyte solutions such as calcium-phosphorous, calcium-magnesium-phosphorous-potassium (CMPK) or others increases the level of one or more of these electrolytes which masks deficiencies. Also blood samples collected for diagnostic purposes must be handled appropriately.  A delay in separating the serum (clear portion of blood) from the red blood cells allows potassium and phosphorous (which are high in red blood cells) to leak into the serum and prevent a diagnosis of deficiency of these two electrolytes. CAHFS recommends taking a blood sample in a red stopper blood collection tube or red and gray stopper separator (gel layer) tube before the animal is treated. The serum (clear portion) that separates off from the red cells should be removed from contact with the red cells within an hour or at most two hours after collection to ensure an accurate result for  potassium and phosphorous. Blood should never be frozen with the red cells still in the tube as this causes red cells to rupture and large amounts of potassium and phosphorous and lesser amounts of calcium and magnesium are released into the serum making electrolyte testing inaccurate.

In recent months, CAHFS has worked with dairies that had a high down cow rate due to low phosphorous which caused alert downer cows that were not responding well to treatment. The initial blood samples tested were taken before electrolyte treatment, refrigerated with the serum left on the clot (red blood cells), and sent to the lab 1 to 3 days after collection. Electrolyte values were normal on these samples. Other blood samples that were submitted within an hour of collection had significantly low phosphorous values. Changes in treatment to include more phosphorous resulted in improved response to treatment and changes in the diet to increase phosphorous resolved the problem.  This real example underscores the importance of submitting good samples to improve diagnostic capabilities.

Testing for electrolytes is performed at our toxicology laboratory in Davis but blood samples can be submitted to any of the four CAHFS laboratory and will be sent to the Davis laboratory.