Use of vitreous humour for postmortem estimation of cattle magnesemia

Abstract

The diagnosis of hypomagnesemic tetany in cattle is based on the clinical history and on findings of hypomagnesemia. Dead animals show no characteristic lesions and postmortem blood samples are not suitable since Mg leaks from the tissues into the blood during autolisis. Magnesium concentration in vitreous humour (VH) reflects the plasma Mg level, and remains unchanged 48 hs postmortem. Therefore, it can be used for postmortem estimation of magnesemia. In a local slaughterhouse, 196 samples were obtained from steers. An eye and a matching blood sample were obtained from each animal. Magnesium was measured in plasma and VH by atomic absorption spectrometry. Magnesium concentration in VH was above plasma concentration in 84% of the samples. Correlation coefficient between plasma Mg and VH Mg was r: 0.51 (F: 69.93 for 1 and 195 degrees of freedom, p<0.001). The regression formula was Y = 0.541 + 0.395 * X, where Y = VH Mg and X = plasma Mg. Although we recommended to bear in mind that any VH Mg value below 0.831 mm gl/l, would be consistent with plasma Mg levels below 0.741 mmol/l, the use of the regression formula allows only a gross estimation of the plasma Mg levels from VH analysis.