USE OF VITREOUS-HUMOR FOR POSTMORTEM ESTIMATION OF CATTLE MAGNESEMIA

The diagnosis of hypomagnesemic tetany in cattle is based on the clini cal history and on findings of hypomagnesemia. Dead animals show no ch aracteristic lesions and postmortem blood samples are not suitable sin ce Mg leaks from the tissues into the blood during autolisis. Magnesiu m 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 sa mples were obtained from steers. An eye and a matching blood sample we re obtained from each animal. Magnesium was measured in plasma and VH by atomic absorption spectrometry. Magnesium concentration in VH was a bove plasma concentration in 84% of the samples. Correlation coefficie nt between plasma Mg and VH Mg was r: 0.51 (F: 69.93 for 1 and 195 deg rees of freedom, p<0.001). The regression formula was Y = 0.541 + 0.39 5 X, where Y = VH Mg and X = plasma Mg. Although we recommended to b ear in mind that any VH Mg value below 0.831 mm gl/l, would be consist ent with plasma Mg levels below 0.741 mmol/l, the use of the regressio n formula allows only a gross estimation of the plasma Mg levels from VH analysis.