Fighting Grass Tetany with High-Mag Mineral Supplement

One of my favorite things about spring is being able to look out my back windows at the house and watch our cattle graze on green grass as opposed to seeing them eat hay in a bare lot.  As pretty as that sight may be, one thought that does haunt me in the spring is the fear of grass tetany.

Livestock may experience this forage-related problem known as grass tetany, grass staggers, lactation tetany, or hypomagnesemia typically in the spring; however it can occur in the fall as well.  Grass tetany is a metabolic disorder caused by reduced magnesium (Mg) levels in the animal’s blood. In cattle, it generally affects older, lactating cows but can also be seen in dry cows, young cows, and in rare cases, growing calves. Symptoms often observed include nervousness, lack of coordination, muscular spasms, staggering, convulsions, coma, milk yield decrease, and death. If you suspect cattle are stricken with grass tetany, a veterinarian should be contacted immediately as early treatment can save animals.

Young cool-season grasses and small grains are commonly associated with this disorder. Farmers should refrain from placing cattle in a field that has been recently fertilized or has resulted in the disease before. Pastures where a significant amount of manure has been applied often have excessive potassium fertility increasing the risk to grass tetany. A farmer can also increase the legume content in his/her pastures with clover or alfalfa since they have higher magnesium levels to compensate for the lack of it in the new lush grass.

Feeding high magnesium or high “mag” mineral supplements is the preferred method to reduce the occurrence of grass tetany. High “mag” mineral mixes are available at most feed stores and contain higher inclusions of magnesium oxide than other complete mineral mixes. Cattle should begin consuming this high “mag” mineral during the late winter months and into early spring when new plant growth is starting. In late spring once temperatures are consistently above 60ºF, a producer can quit feeding the high “mag” mixtures. High mag mineral does not need to be fed year round, but is not problematic if it is. Free-choice high mag mineral should contain 12 to 15% magnesium from magnesium oxide. Cattle need to consume four ounces of the mineral supplement daily. Magnesium oxide is unpalatable, which can result in low mineral intake. Co-product feedstuffs such as dried distillers grains, molasses or a flavoring agent is added to the mineral mix to increase palatability.

If free-choice mineral is not a viable option, producers can also mix their own supplement by adding the appropriate amount of magnesium oxide to another palatable feedstuff, i.e. feeding in or with 1 to 2 lbs. of corn or other by-product that provides 20-25 grams of magnesium. For dairy cows, magnesium oxide can be added to the grain mix to provide an intake of 20 g of magnesium per cow per day. Magnesium oxide may be routinely used as a buffer in these grain mixes for dairy cows, so producers should check with their nutritionist to make sure adequate amounts and proper sources are being used to prevent grass tetany.

Besides magnesium oxide, another source of Mg is magnesium sulfate, which is more palatable than magnesium oxide. The downside to feeding magnesium sulfate is it can be an issue where cattle are consuming high sulfate water or other feedstuffs high in sulfur. Producers that are feeding corn co-products (distiller’s grains or corn gluten feed), adding additional sulfur to the diet in the form of magnesium sulfate, or have high sulfur water could create a sulfur toxicity.

The season for grass tetany is upon us so to reduce health problems and livestock death to this disorder, it is important to provide a quality high “mag” mineral or supplement containing Magnesium oxide.  For more information about grass tetany, contact the McLean County Cooperative Extension Service at (270)273-3690.  Educational programs of the University of Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin.

Upcoming Events
April 16th Farmers’ Market Meeting, 3pm Ag Office at Extension Office (use side door)
April 21st Plant Swap & Sale Committee Meeting, 3pm
April 21st Ag Festival Committee Meeting, 5pm
April 29th Poultry Producers Meeting, 9:30am Myer Creek Park
April 30th CPH Sale
May 9th Plant Swap & Sale, 8am-1pm Myer Creek Park
May 12th Wheat Field Day, Princeton Research Station
June 2nd Opening Day of Farmers’ Market