Subclinical hypocalcemia is a threat to transition cow health, and there is evidence that it is a greater threat than previously thought.

Until recently, the prevalence of subclinical hypocalcemia in fresh cows was unknown, explains Heather Dann with the W.H. Miner Agricultural Research Institute in Chazy, N.Y.

To assess its prevalence, researchers collected blood from 1,462 cows (480 herds in 21 states) within 48 hours of calving and analyzed for calcium. Surprisingly, 47 percent of cows had subclinical hypocalcemia, which was defined as serum calcium < 2.0 mM or < 8 mg/dL. Cows did not have clinical signs of milk fever. Subclinical hypocalcemia increased with age and was present in 25%, 41%, 49%, 51%, 54% and 42% of first through sixth lactation cows, respectively. The normal homeostatic response to hypocalcemia may have limits with a cow’s age and may contribute to greater or prolonged hypocalcemia in older cows.

Dann explains more in the December 2012 Miner Institute Farm Report.