How to Tackle Grass Tetany in Cattle

Grazing in the spring often leads to a loss of production in dairy cows. Grass tetany may be the cause. Grass tetany causes a decrease in appetite, milk production and milk fat content.

Grass tetany is a serious condition in cattle caused by low magnesium levels. It usually happens in spring when cows graze on young grass that doesn’t have enough magnesium. Visible symptoms of grass tetany in cattle include restlessness, muscle twitching, unsteady movement, and in severe cases, collapse or even death. Farmers can give cows magnesium supplements, manage their grazing, and reduce stress to prevent it.

Young grass in pasture is rich in soluble nitrogen and fermentable carbohydrates, low in cellulose, and the magnesium to potassium ratio (Mg2+/K+) is low. As a result, the intra-ruminal absorption of magnesium decreases. This puts the cow at risk of grass tetany. The disease presents a high risk for dairy cows during the first two months of lactation. Animals come out of a long period in the stall and experience weight loss after calving.

Wynnstay Premier Cattle Mag is formulated for use where there is a risk of grass staggers in cattle during the key spring months. 

Low ingestion and low temperatures can trigger a large adrenaline rush. This leads to a rapid energy requirement with a sudden mobilisation of lipid reserves, and a decrease in the concentration of magnesium in blood plasma, causing grass tetany. This disease is characterised by neuromuscular and digestive disorders, accompanied by a decrease in intake and milk production. In the most severe cases, the animal may die.

During the grazing period, the presence of fermentable carbohydrates, combined with a low proportion of cellulose in the young grass leads to a high production of volatile fatty acids in the rumen. Their accumulation causes a drop in rumen pH, which can lead to ruminal sub-acidosis. Namely a pH < 5.8 for more than 3 hours. This low pH can cause a decrease in feed intake, milk production and the milk fat content. The cost of production therefore increases. The economic loss is estimated, on average, at 1€ per cow per day (Plaizier et al., 2008).

To reduce the risk, ruminants need an increased intake of rumen-soluble magnesium. The magnesium present in pHix-up at 48.5%, is a highly soluble source of Mg2+ for ruminants during the risk period of grass tetany. Furthermore, pHix-up has an acid neutralization capacity of 39.0 meq/g and a rapid and sustained effect of ruminal pH, which means it is perfectly suited for high yield dairy cows.

The positive effect of pHix-up on ruminal pH has been demonstrated in tests involving more than 10,000 dairy cows worldwide. Milk and total fat production also increases with pHix-up. On average, ECM (Energy Corrected Milk) and total fat were increased (p < 0.001) by 1.2 kg and 50 g per cow per day.

Rayburn E., Matlick D., 2012. Reducing the risk of grass tetany, West Virginia University. Elliott M., 2009. Grass tetany in cattle – treatment and prevention, Extensive Industries Development, Primefact 421.  Grunes D.L., Mayland H.F., Controlling grass tetany, Agricultural Research Service and Extension, United States Department of Agriculture, Leaflet nr. 561.  NRC 2001; INRA 2018