Home on the range: Green grass caution

Chanda Engel SDSU Cow Calf Field Specialist
Farm Forum

As we enter the last week of April, the lingering of winter has many weary from long days and nights slogging through snow, slush and mud. Some sunshine and the hope of green grass will do much to lift the spirits of cattle caretakers in the area. However, a bit of caution about the importance of letting the grass get a bit of a head start before allowing cattle the luxury of grazing it. Not only will this assist with the production and sustainability of the pasture, but it may assist with avoiding potential grass tetany issues in cattle.

Grass tetany is a nutritional metabolic disorder caused by low blood magnesium levels. It primarily affects older ruminant animals (sheep and cattle) at early stages of lactation, but may occur in younger lactating, dry, or growing animals. Tetany occurs most frequently when livestock are grazing lush and immature grass, particularly in the spring, often following cool periods (temps between 45 and 60 degrees F) when grass is growing rapidly. However it is also seen in the fall with new growth of cool season grass or wheat pastures.

Low blood magnesium may be caused by:

• A diet low in magnesium.

• A diet with nutrient imbalances that interfere with magnesium metabolism.

• Higher levels of milk production. When blood magnesium drops too low, proper nerve impulse transmission fails, causing the disorder.

The following signs and symptoms have been observed in livestock affected by tetany:

• Grazing away from the herd.

• Irritability.

• Muscular twitching in the flank.

• Wide-eyed and staring.

• Muscular in-coordination.

• Staggering.

• Collapse.

• Thrashing.

• Head thrown back.

• Coma.

• Death.

Animals on pasture are often found dead without illness having been observed. Generally, evidence of thrashing will be apparent if grass tetany is the cause of death. The cause of death may be confirmed by collecting a urine sample from the bladder during postmortem examination. The magnesium concentration in the urine is very low when grass tetany was the cause of death.

The prevention of grass tetany depends largely on avoiding conditions that bring it on:

• Hold animals off new grass until it is 4-6” tall.

• Feed dry hay or grain until grass can provide adequate nutrition.

• Maintain animals on a moderate plane of nutrition until ample grass is available.

• If possible, feed some legume hay or graze early legume pasture, since legumes are higher in magnesium than grass.

• Supplement with high magnesium mineral.

Supplementation increases blood magnesium levels and alleviates much of the grass tetany problem. Magnesium should be consumed on a daily basis. Livestock that are afflicted with grass tetany need to be treated immediately. The most common treatment is an intravenous injection of a dextrose solution containing both magnesium and calcium. I would suggest consulting your veterinarian regarding recommended preparations, dosages, and administration.

Decreasing and preventing animal losses from grass tetany depends on using one or more of the suggested preventative management practices, and timely treatment of affected animals. Lastly, I want to encourage livestock caretakers to hang in there and to take care of themselves as well.

“Ever tried, ever failed—No matter. Try again! Fail again, fail better.” — Samuel Beckett