Determination of total and ultrafilterable calcium and magnesium in normal equine serum

Total and ultrafilterable calcium (Ca) and magnesium (Mg) values were determined for Shetland pony stallions, stallions, and pregnant and diestrous mares, using a simple, inexpensive, quick procedure to obtain an ultrafiltrate of serum. There was no significant difference between horses and ponies, between stallions and mares, or between pregnant and nonpregnant mares. The percentage of total serum Ca that was ultrafilterable was 63.4+/-1.7 for horses and 64.8+/-2.2 for ponies. The percentage of total serum Mg that was ultrafilterable was 75.6+/-1.5 for horses and 77.0+/-1.7 for ponies. Total serum Ca was 12.56+/-0.26 mg/dl for horses and 12.43+/-0.32 mg/dl for ponies. Total serum Mg was 2.18+/-0.29 mg/dl for horses and 2.49+/-0.60 mg/dl for ponies. This technique can be coupled with specific assays for ionized forms of the cations or with ion electrodes to obtain values for protein-bound, ionized, or complexed and chelated Ca and Mg in equine serum.