Visit with a Vet: New Tool for Monitoring Blood Calcium Concentrations in Dairy Cattle

Originally published in the Feb. 19, 2014, issue

 

Visit with a Georgia veterinarian in this monthly feature. This edition comes from Dr. John K. Bernard, animal and dairy science professor on the UGA-Tifton campus. 

 

Hypocalcemia, known as milk fever, is a condition of low blood calcium concentration that negatively affects performance and health in dairy cattle. Cows with clinical milk fever are more likely to have other diseases including retained placenta, mastitis, ketosis and left displaced abomasum, or LDA. Though the incidence of milk fever has declined to approximately five percent with improved close-up dry cow nutrition, it is estimated that 50 percent of all dairy cows in the US experience subclinical hypocalcemia. Cows with subclinical hypocalcemia have lower milk yield, decreased reproductive performance and increased odds of ketosis and LDA.

 

Blood sample analysis is the traditional way of evaluating a dairy cow’s calcium status. The sample is analyzed for total calcium concentrations. This is calcium that meets three specifications: bound to plasma protein; in an ionic form associated with low molecular weight compounds; and free ions. Metabolic functions such as muscle contraction, blood clotting and bone formation is supported by the free ion form of calcium.

 

Ionized calcium measures these free calcium ions, which are readily available for the aforementioned metabolic functions. This provides a better estimate of true calcium status. The proportion of total calcium that is ionized is not constant, and changes with lactation stages. Occasionally, some calcium concentrations indicate the cow is not ill, but looking at ionized calcium concentrations confirm she is in a state of clinical hypocalcemia.

 

Ionized calcium concentrations of less than one millimol per liter are considered indicators of subclinical milk fever. Both ionized calcium and magnesium levels can be used to evaluate nutrition in close-up dry and transition cow nutrition, as well as diagnose milk fever and grass tetany that occur around parturition or early lactation.

 

Recently, an electrode-based method was developed for rapid measurement of ionized calcium. This method is both economical and available to researchers and producers, and a unit is located at the University of Georgia Veterinary Diagnostic and Investigational Laboratory in Tifton, Ga.

 

Samples of ionized calcium and magnesium should be collected in a green top (Lithium Heparin) with a separator gel Vacutainer tube, or a “tiger-top” gel-separator tube. The sample should be allowed to clot, centrifuged to separate the plasma or serum from the blood clot and refrigerated immediately. The frozen sample should be packaged with an ice pack and shipped for overnight delivery to the laboratory for analysis. The pH of the sample is measured and used to calculate the final result.

 

Do not remove the cap from the collection tube. Exposing samples to air or long storage can change blood pH, so it is important to collect and transmit and process samples quickly in a laboratory to obtain valid results. 

 

For questions about submitting ionized calcium and magnesium samples, contact Anita Merrill at 229-386-3340.