Grass Tetany in Beef Cows

Grass tetany usually strikes lactating cows on fast-growing spring grass, and it can kill within hours. Prevention depends on knowing the risk and talking with your nutritionist before turnout.

Key points

Grass tetany is a magnesium-related metabolic emergency, not a contagious disease.
Older lactating cows on lush spring forage are at greatest risk.
Work with a nutritionist to set up mineral supplementation before turnout.
Watch herds daily in cool, wet, fast-growth weather.
A down cow needs a veterinarian immediately.

What grass tetany is

Grass tetany is a metabolic problem tied to low blood magnesium. It is not an infection, and it does not spread from cow to cow. It happens when the cow's magnesium needs are high and what she is taking in cannot keep up.

It is sometimes called grass staggers. The names point to the same urgent problem: a cow that was normal in the morning can be down by afternoon.

Which cows are at highest risk

Older, lactating cows nursing calves are the classic case, especially in early lactation when milk production pulls heavily on mineral reserves. Young cattle and dry cows can be affected, but they are less common.

Risk climbs during cool, cloudy, wet spells when pasture is growing rapidly. Lush small grains and cool-season grasses are often involved, and heavy nitrogen or potassium fertilization can make forage less favorable for magnesium absorption.

Signs you cannot ignore

Early signs are easy to miss in a big pasture. Cows may graze away from the herd, look nervous, or show an odd, stiff walk. As it progresses, you may see twitching, staggering, collapse and paddling.

At that stage the cow is in an emergency. Move slowly and call the veterinarian right away. Excited handling can make things worse, and some animals die with little warning.

Cow separated from the herd and alert but jumpy
Muscle twitching, especially around the face and ears
Stiff, stumbling or uncoordinated gait
Collapse, convulsions or paddling
Sudden death in a lactating cow on lush grass

Prevention before turnout

The best moment to act is before cattle go onto risky pasture. Work with a nutritionist or your extension specialist to plan magnesium supplementation through a mineral program that suits your forage and your herd. Do not guess at amounts. Ask for the target intake that fits your situation and a method to make sure cows actually eat it.

Supplement has to be available before the risk period starts, since cows need time to adjust to a new mineral and some find it less appealing.

Write the plan down and tape it inside the feed room door. A simple sheet that lists the pastures, the mineral feeder locations, the date supplement starts and who checks intake means the plan survives a busy spring or a hired hand who is new to the place.

Have a nutritionist review your forage and mineral program
Start supplementation ahead of spring turnout, not after the first case
Make sure every cow can reach mineral without being crowded off
Check intake and adjust with professional advice
Consider fertilization practices on high-risk pasture

Managing pasture and groups

Put the highest-risk cows, usually older cows with young calves, on safer forage when you can. A grass and legume mix or hay fed alongside lush pasture can lower the risk. Delaying turnout on very lush growth is another option your extension agent may suggest.

Walk the herd daily during high-risk weather. A short check at the right moment may save a cow.

If you find a down cow

Call your veterinarian immediately. Veterinary treatment is the only reliable response, and it needs to be given carefully, so this is not a job for home remedies or guesswork. Keep the cow calm, protect her from injury and keep other animals away.

Afterward, ask your vet to help you work out why it happened, since one case often means others are close behind. Any meat or milk withdrawal times set on the label or by your vet must be followed exactly.

Common mistakes

Waiting for the first case before starting supplementation is the most common error. Others include assuming all mineral mixes are equal, putting out too little mineral for too many cows, and ignoring the weather pattern. Keep notes on where and when cases occur so next year's plan starts earlier.

Share the warning with neighbors who lease your ground or help at calving. A cow lost on a pasture you do not see every day often goes unnoticed for hours, so more eyes on the herd during risky weather is a real safeguard.

When to get help: Ask your nutritionist or extension specialist to design a mineral program for your forage, and call your veterinarian at once for any cow that is staggering, twitching or down. Follow all label or vet-set withdrawal times for treated cows.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

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