Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in sheep

Hypomagnesaemic tetany was induced in non-lactating and lactating ewes by f eeding them semi-synthetic low magnesium diets containing additional potass ium chloride and citric acid. Aqueous and vitreous humour were sampled from one eye at the time of death (fresh) and from the second eye after the hea d had been stored at ambient temperature for 24 hours (24-hour). There were significant relationships between the concentrations of magnesium in cereb rospinal fluid and plasma and its concentrations in fresh aqueous humour an d fresh vitreous humour. Magnesium concentrations of <0.33 mmol/litre in fr esh aqueous humour and <0.50 mmol/litre in 24-hour aqueous humour were asso ciated with severe hypomagnesaemia and tetany. However, the concentration o f magnesium in aqueous humour is relatively unstable and, unless the time o f death was known accurately, its interpretation would be difficult. Magnes ium concentrations of <0.60 mmol/litre in fresh vitreous humour and <0.65 m mol/litre in 24-hour vitreous humour were associated with severe hypomagnes aemia and tetany in adult sheep. The concentration of magnesium in vitreous humour was relatively stable for up to 48 hours postmortem.