High-Risk Groups: Lactating beef cattle on winter pastures.
Clinical Signs:
Neuromuscular: Muscle weakness, fasciculations (twitching), seizures, ataxia, and belligerent behavior.
Cardiac: Ventricular arrhythmias.
Critical: Coma and sudden death.
Hypermagnesemia (Magnesium Excess)
Cause: Primary cause is oversupplementation.
Clinical Signs: Can lead to secondary hypocalcemia, weakness, cardiac arrhythmia, and death.
Diagnostics:
Serum Testing:
Total Magnesium (tMg): Divided into ionized, protein-bound, and chelated forms.
Ionized Magnesium (iMg2+): The physiologically active (free) fraction. It must be measured directly and cannot be accurately calculated from tMg.
Urine Assessment:
Fractional Clearance: Uses spot samples of urine and serum to assess renal excretion without timed collections.
The "Gold Standard":IV Magnesium Retention Test. Deficient animals retain a high proportion of an administered dose, while healthy animals excrete most of it.
Therapeutic Uses in Horses:
Cathartic: High dosages used to treat large-intestinal impactions.
Neurological: Lower dosages shown to decrease trigeminal-mediated head shaking.