Optimag Bolus. 10 per pack. Each Bolus will supply 100g of magnesium over a four week period.These magnesium bullets are targeted at preventing hypomagnesaemia (grass tetany) in dairy cattle. They should be administered before the major risk periods of grass tetany. These risk periods include after calving when cows are grazing lush early spring grass. Use a suitable dosing gun to put 2 boluses into the back of the mouth at the same time. Take care during administration to avoid injury to the mouth and pharynx. Always ensure the animal swallows the boluses. Only to be given to cattle at least 300kg bodyweight. Administer orally by using the specially designed bolus gun.