Grass tetany is a metabolic disease involving magnesium deficiency that usually occurs in ruminant livestock after grazing on pastures of rapidly growing grass, especially during spring season.

Symptoms of Grass Tetany

Progressive symptoms include cows grazing away from the herd, irritability, constant muscle twitching, cows collapsing, head thrown back, and coma, followed by death eventually.

Causes of Grass Tetany

The condition usually results from hypomagnesemia (low magnesium concentration in blood). This usually happens when there is a low magnesium intake, low magnesium absorption, abnormally low retention of magnesium or a combination of all of above. High potassium and nitrogen (protein) levels in spring grasses will also affect the magnesium availability to the cows. It is a challenge to use forage test to identify the risk of grass tetany due to the rapid change of spring pastures.

The cows are at their greatest risk of grass tetany in spring season. This is especially true when the skies are cloudy and soils are cool. Risk are further increased with highly fertilised, permanent cool-season pastures or annual seeded grasses like wheat or ryegrass. In general, the older lactating cows face higher risk of grass tetany compared to younger cows.

With that being said, grass tetany is preventable. Here are some of our proposed solutions.

Prevention of Grass Tetany

The first thing to do is to feed the cows with magnesium supplement which will help combat the magnesium deficiencies associated with lush spring grass. It is highly recommended to offer the cows mineral supplements 2 - 3 weeks before they are first exposed to lush grass to achieve consistent intake of mineral supplements before the time of highest risk. Continue feeding for 60 days after the first sign of grass growth.

Another way to prevent grass tetany is grazing less susceptible young cows on the highest risk pastures while holding the older and more matured lactating cows off pastures until they are at least 4 - 6 inches tall.

If you wait until the cows shows symptoms of grass tetany, it may be too late to save them. It is best to prevent grass tetany in the first place..