Hypomagnesemic tetany is common in young calves that are stall fed with poor quality hay during winters. In the video a calf is seen in opisthotonos position in advanced tetany due to low blood magnesium levels. The calf was administered a 10% solution of Magnesium Sulphate which led to its recovery.

Such symptoms are rare to be seen because animals usually die very quickly once the blood levels of Mg fall. The normal levels in calves are in the range of 2 to 2.5mg/100 ml of blood and signs of tetany start developing once the levels fall below 0.8mg/100ml. Recurrence is almost certain and the condition needs long term supplementation for its treatment. Low levels of Mg affect production of Parathyroid hormone too and usually hypocalcemia accompanies the condition.

Source: Tulmulla, Gandarbal