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  • Author or Editor: Francisco J. Mendoza x
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Objective—To establish reference values for protein-bound, ionized, and weak-acid complexed fractions of calcium and magnesium in equine serum and determine stability of ionized calcium (iCa) and ionized magnesium (iMg) in serum samples kept under various storage conditions.

Animals—28 clinically normal horses.

Procedure—Total calcium (tCa) and magnesium (tMg) in equine serum were fractionated by use of a micropartition system that allows separation of protein-bound calcium (pCa) and magnesium (pMg) and ultrafiltrable calcium (μCa) and magnesium (μMg) fractions. Serum concentrations of iCa and iMg were measured in the ultrafiltrate by use of selective electrodes. Serum concentration of complexed calcium (cCa) or magnesium (cMg) was calculated by subtracting iCa or iMg from μCa or μMg, respectively.

Results—Mean ±SE serum tCa concentration was 3.26 ± 0.06 mmol/L. Calcium fractions were as follows: pCa, 1.55 ± 0.03 mmol/L (47.4 ± 0.9%); iCa, 1.58 ± 0.03 mmol/L (48.5 ± 0.7%); and cCa, 0.13 ± 0.02 mmol/L (4.1 ± 0.9%). Serum tMg concentration was 0.99 ± 0.04 mmol/L. Magnesium fractions were as follows: pMg, 0.33 ± 0.04 mmol/L (33.3 ± 4.2%); iMg, 0.57 ± 0.02 mmol/L (57.6 ± 1.7%); and cMg, 0.09 ± 0.02 mmol/L (9.1 ± 1.9%). Refrigeration (4°C) did not affect iCa values, whereas iMg declined by 8% after 120 hours. Neither iCa nor iMg was affected by freezing (−20°C).

Conclusions and Clinical Relevance—In equine serum, iMg is less stable than iCa; thus, when serum samples are not going to be analyzed promptly, freezing may be preferable to refrigeration for storage.

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in American Journal of Veterinary Research


Objective—To provide reference values for serum biochemical variables that are used for evaluation of mineral metabolism in donkeys and compare values with those in horses.

Animals—18 donkeys and 18 horses.

Procedures—Total calcium (tCa), total magnesium (tMg), and inorganic phosphorus (P) concentrations were measured in serum samples via spectrophotometry. Ionized calcium (iCa) and magnesium (iMg) concentrations were quantified with selective electrodes. By use of a micropartition system, tCa and tMg were fractionated to separate protein-bound (pCa, pMg) and ultrafiltrable fractions. Complexed calcium (cCa) and magnesium (cMg) concentrations were calculated by substracting ionized fractions from ultrafiltrable fractions. Parathyroid hormone (PTH) and calcitriol (CTR) concentrations were measured via radioimmunoassay.

Results—Serum tCa concentration in donkeys (3.37 ± 0.21 mmol/L) was composed of pCa (1.59 ± 0.21 mmol/L [47.0 ± 4.2%]), iCa (1.69 ± 0.04 mmol/L [50.4 ± 3.0%]), and cCa (0.09 ± 0.08 mmol/L [2.6 ± 2.9%]). Serum tMg concentration (1.00 ± 0.08 mmol/L) was fractioned in pMg (0.23 ± 0.08 mmol/L [23.4 ± 8.1%]), iMg (0.59 ± 0.04 mmol/L [58.8 ± 5.1%]), and cMg (0.18 ± 0.08 mmol/L [17.8 ± 7.2%]). Serum concentrations of P (1.14 ± 0.30 mmol/L), PTH (20.4 ± 21.2 pg/mL), and CTR (13.4 ± 5.9 pg/mL) were determined.

Conclusions and Clinical Relevance—Serum variables of mineral metabolism in donkeys were within reference ranges for horses. However, when compared with horses, donkeys had higher iCa, cMg, and CTR and lower pMg and PTH concentrations.

Full access
in American Journal of Veterinary Research