Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in cattle

Severe hypomagnesaemia and tetany were induced in 10 lactating cows by feed ing them semi-synthetic low magnesium diets and the animals were used to st udy the stability of postmortem markers of hypomagnesaemic tetany. There we re significant relationships between the concentrations of magnesium in eit her cerebrospinal fluid (CSF) or plasma and either aqueous or vitreous humo ur. The onset of hypomagnesamic tetany was also associated with low magnesi um concentrations in plasma, CSF and aqueous and vitreous humour. Magnesium concentrations less than 0.25 mmol/litre in fresh aqueous humour may be in dicative of severe hypomagnesaemia and possible tetany in lactating cows, b ut the concentration of magnesium in aqueous humour was unstable postmortem . The concentration of magnesium in vitreous humour was relatively stable a nd a concentration of less than 0.55 mmol/litre could be used as a diagnost ic marker of tetany in cattle for up to at least 48 hours postmortem, at am bient temperatures typical of Northern Ireland.