Magnesium is a co-factor of many enzymatic systems in animal's body, and also a component of skeleton. Symptoms when animals lacking magnesium are stress anaphylaxis, muscle crispation, unwilling stand-up, balance maladjustment and twitch. Specifications: 1) MgSO4.7H2O: Mg≥9.7, Pb≤0.001, As≤0.0002 2) MgSO4.H2O: Mg≥16.0, Pb≤0.001, As≤0.0002