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Watch cattle for grass tetany this spring

Janna Kincheloe, MSU Extension Judith Basin County Agent

The arrival of spring grass combined with cool and rainy weather has created prime conditions for grass tetany in cattle. Sometimes called grass staggers or hypomagnesemia, grass tetany is a metabolic disorder related to a magnesium (Mg) deficiency.

Animals come down with grass tetany most often after grazing rapidly growing, lush cool-season grasses or small grain pastures in spring and fall. Tetany is not common on legume pastures. Grass tetany can also occur when cattle are wintered on low Mg grass or cereal grain hay. The risk should decrease if animals are fed a grass-legume hay.

Older cows in early lactation cows are typically the most susceptible to tetany, compared to younger cows. Younger cows can mobilize Mg reserves from their bones more readily than older cows to help resolve deficiency issues. To prevent grass tetany, animals should be fed a high Mg supplement or free-choice mineral containing 8 to 12 percent Mg. Most magnesium compounds are unpalatable to cattle when offered alone, and need to be added to a protein supplement, grain mix, liquid supplement, or salt. In general, incorporating Mg with salt is very effective since cattle naturally have an appetite for salt, especially when grazing lush grasses. Intake of both salt and magnesium will increase magnesium absorption.

Dr. John Paterson, Montana State University Extension Beef Cattle Specialist, recommends feeding 2 to 4 ounces of high magnesium mineral supplement per day to prevent tetany. “Since magnesium can be unpalatable, it is important to feed mineral mixed with at least 20 percent salt for approximately 30 days prior to spring grazing to allow cows to increase consumption to target levels,” he said.

Grass that is susceptible to producing grass tetany often is low in magnesium (Mg), calcium (Ca), and sodium (Na), but higher in potassium (K).

Paterson notes that forages with a “tetany ratio” [basically the millequivalents of K/(Ca + Mg)] of greater than 2.2 can increase the occurrence of tetany.

A forage analysis can be run on forages to determine the tetany ratio. “I recommend that ranchers make sure their mineral supplement also has at least 12 percent calcium to reduce the risk of tetany even further,” he said.

In severe cases of grass tetany, symptoms are not evident and the animal typically dies. In some mild cases, symptoms include decreased milk yield, nervousness, and staggering. They may also lie down and get up frequently. Cattle are easily excited at this point and may respond to stimulus by continuously bellowing or running. They will have a staggered gait pattern, followed by collapse, stiffening of muscles, and convulsions. Animals usually die during or after a convulsion unless treatment is given. Treatment of cows in the early stages of grass tetany can be effective, but animals should be handled quietly and gently to create the least amount of stress and exertion possible. Any stress that causes excitement such as driving or roping can result in sudden death. A sterile solution of magnesium sulfate given subcutaneously is a common treatment. Producers should contact their veterinarian to discuss other treatment options.

The arrival of spring grass combined with cool and rainy weather has created prime conditions for grass tetany in cattle. Sometimes called grass staggers or hypomagnesemia, grass tetany is a metabolic disorder related to a magnesium (Mg) deficiency.

Animals come down with grass tetany most often after grazing rapidly growing, lush cool-season grasses or small grain pastures in spring and fall. Tetany is not common on legume pastures. Grass tetany can also occur when cattle are wintered on low Mg grass or cereal grain hay. The risk should decrease if animals are fed a grass-legume hay.

Older cows in early lactation cows are typically the most susceptible to tetany, compared to younger cows. Younger cows can mobilize Mg reserves from their bones more readily than older cows to help resolve deficiency issues. To prevent grass tetany, animals should be fed a high Mg supplement or free-choice mineral containing 8 to 12 percent Mg. Most magnesium compounds are unpalatable to cattle when offered alone, and need to be added to a protein supplement, grain mix, liquid supplement, or salt. In general, incorporating Mg with salt is very effective since cattle naturally have an appetite for salt, especially when grazing lush grasses. Intake of both salt and magnesium will increase magnesium absorption.

Dr. John Paterson, Montana State University Extension Beef Cattle Specialist, recommends feeding 2 to 4 ounces of high magnesium mineral supplement per day to prevent tetany. “Since magnesium can be unpalatable, it is important to feed mineral mixed with at least 20 percent salt for approximately 30 days prior to spring grazing to allow cows to increase consumption to target levels,” he said.

Grass that is susceptible to producing grass tetany often is low in magnesium (Mg), calcium (Ca), and sodium (Na), but higher in potassium (K).

Paterson notes that forages with a “tetany ratio” [basically the millequivalents of K/(Ca + Mg)] of greater than 2.2 can increase the occurrence of tetany.

A forage analysis can be run on forages to determine the tetany ratio. “I recommend that ranchers make sure their mineral supplement also has at least 12 percent calcium to reduce the risk of tetany even further,” he said.

In severe cases of grass tetany, symptoms are not evident and the animal typically dies. In some mild cases, symptoms include decreased milk yield, nervousness, and staggering. They may also lie down and get up frequently. Cattle are easily excited at this point and may respond to stimulus by continuously bellowing or running. They will have a staggered gait pattern, followed by collapse, stiffening of muscles, and convulsions. Animals usually die during or after a convulsion unless treatment is given. Treatment of cows in the early stages of grass tetany can be effective, but animals should be handled quietly and gently to create the least amount of stress and exertion possible. Any stress that causes excitement such as driving or roping can result in sudden death. A sterile solution of magnesium sulfate given subcutaneously is a common treatment. Producers should contact their veterinarian to discuss other treatment options.


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