Minerals are a crucial component in beef cattle diets. While mineral mixtures may vary among farms, there is one mineral that is on many minds this time of year: magnesium (Mg). Magnesium is essential for optimal growth, reproduction and development, and is found in bones, teeth and soft tissues. Grass tetany or grass staggers, sometimes called hypomagnesemia, is a disorder associated with low magnesium levels in the blood and cerebrospinal fluid. The disorder is most often seen in animals grazing cool-season annual and perennial grasses and especially affects animals in early lactation. The occurrence of grass tetany is most prominent in late winter and early in the spring as forage starts to green up and grow rapidly.
Common symptoms of grass tetany are nervousness, muscle twitching, staggering, and the animal may go down on its side with muscle spasms and convulsions. Often, when cattle are found dead due to grass tetany, the illness was not actually observed because death can result very quickly after symptom onset. Older animals with young calves are particularly susceptible because when magnesium levels drop, they cannot mobilize magnesium from bones like a young animal. Grass tetany can still affect young or dry cows and growing calves, but it is better to graze these animals on higher-risk pastures. The most dependable form of control is supplying a mineral supplement with a relatively high concentration of magnesium.
Standard mineral mixes typically have between 1% and 4% magnesium, whereas “hi-mag” minerals typically have around 12% to 14%. Across the Southeast, the most common time to see grass tetany is mid-February through mid-April, so this coincides with the time that high-magnesium mineral should be fed to cattle. Magnesium is not stored in the body, so it is pertinent for cattle to meet their intake requirements daily. General guidelines for supplementing magnesium can be found below:
- Provide at least 1 ounce per day of magnesium oxide to yield at least 0.6 ounce of magnesium.
- The supplement should contain either magnesium oxide or magnesium sulfate (not magnesite or dolomitic limestone).
- Loose mineral mixtures are preferred in situations where there is a history of grass tetany.
- Keep hay available until cattle completely stop consuming it.
- After starting cattle on high-magnesium supplements, continue until “danger” is past in the late spring.
To prevent grass tetany, it is recommended to have magnesium intake at about 0.6 ounce per day. While some magnesium will be supplied by forage and feed, it may be desirable to obtain most or all of this level from supplemental mineral, especially in high-risk situations. Remember the Benjamin Franklin quote: “An ounce of prevention is worth a pound of cure."
