Calving season is officially over at our house, for the most part! As we worked cows and calves to go to grass. I was the keeper of the calving book, the Holy Grail of all the important details. It was a big responsibility, but I thought I was up for the task. Obviously, my husband didn’t think so. He instructed me to put the book in a zippered pocket. I think you know where this is going. It turns out that our KSU Calving books don’t go through the washer and dryer very well! The minute I opened the dryer and saw the extreme amount of “lint,” I knew what I had done! Thankfully, I can reconstruct with computer spreadsheet. I may never live this down!
It is always a relief to get the cattle out to pasture. Dr. Steve Ensley, KSU Vet Diagnostician, told me once, there aren’t many reasons to have dead livestock in the pasture. But, one of them this time of year is grass tetany.
Grass tetany is a serious problem in many livestock herds. It is characterized by low blood serum levels of magnesium from a dramatic deficiency of this mineral in forages and pastures. Symptoms of grass tetany — winter tetany, grass staggers, magnesium tetany — usually first appear as extreme nervousness, an awkward gait, muscle spasms and collapse. The symptoms may progress rapidly.
Therefore, sometimes no clinical signs are observed and a cow may simply be found dead. Other symptoms may include grinding the teeth, violent convulsions and coma. Cows suffering from grass tetany may often resemble those with cases of milk fever and have low calcium as well as low serum magnesium levels. A positive diagnosis is difficult to obtain, but the status of the herd may be evaluated through blood samples. Serum magnesium levels below 1.0 mg per 100mL would indicate magnesium levels low enough to result in grass tetany.
Grass tetany can occur at almost any time of the year, but most often will occur in April and May in our area. Other conditions which are favorable to the incidence of grass tetany include:
• Warm temperatures in early spring followed by cool, cloudy weather.
• It occurs more often in cows 6 years old or older nursing calves under two months of age.
• Grass pastures which contain few or no legumes are the most likely to cause grass tetany.
• Soil types that have a high level and availability of potassium are related to increased cases of grass tetany.
So how can you prevent grass tetany?
Keep magnesium additions to mineral supplements available from May until October. Commercial mineral mixes that are high in magnesium are readily available. A mix can be made at home, which also features a selenium supplement, with the following recipe (Wahlberg, 1995): 22.5 percent trace-mineralized salt, 22.5 percent dicalcium phosphate, 10 percent of a 0.06 percent selenium mix, 22.5 percent magnesium oxide and 22.5 percent ground corn. Cattle should eat about one-fourth of a pound of the mixture daily.
Wait until early spring grass growth reaches 8-10 inches before grazing.
Graze grass-legume pastures first in the spring. Cases of grass tetany are seldom seen when legumes are included in pastures.
Graze heifers, stockers and dry cows on high-risk pastures.
Identify cows that suffer from grass tetany as they tend to be more susceptible in following years.
Cows that suffer from grass tetany and go down for more than 12 hours seldom recover. Those in earlier stages should be handled gently and quietly. Stress and exertion will often cause infected animals to go down or die suddenly.
An emergency treatment includes preparing 200 mL of a saturated solution of epsom salts. This solution should be injected under the skin of the animal in at least multiple sites with 10 mL injected at each site. A veterinarian should be consulted to provide intravenous magnesium supplements.