Much of Oklahoma and the Southern Plains should have wheat pasture to utilize as winter feed for stocker cattle, replacement heifers and, in some cases, for adult cows. At -- and after -- calving time next January, February and March, "grass tetany" could occur in a few situations. Planning ahead now could reduce the risk of grass tetany during the spring calving season.
Grass tetany typically occurs in beef cows during early lactation and is more prevalent in older cows. The reason older cows are thought to be vulnerable is due to the fact that they are less able to mobilize magnesium reserves from the bones than are younger cows.
Symptoms include incoordination, salivation, excitability (aggressive behavior toward humans) and, in final stages, tetany, convulsions and death.
It is known that factors other than simply the magnesium content of the forage can increase the probability of grass tetany. High levels of potassium in forages can decrease absorption of magnesium and most lush, immature forages are high in potassium. High levels of nitrogen fertilization also have been shown to increase the incidence of tetany although feeding protein supplements has not. Other factors such as the presence of certain organic acids in tetany-causing forages have been linked with tetany.
When conditions for occurrence of tetany are suspected, cows should be provided mineral mixes containing 12 to 15 percent magnesium and be consumed at 3 to 4 ounces per day. It is best for the supplements to be started a couple of months ahead of the period of tetany danger so that proper intake can be established. Because tetany also can occur when calcium is low, calcium supplementation should also be included.
Cows grazing lush small grain pastures should be fed mineral mixes containing both calcium and magnesium.
Learn more about mineral nutrition of grazing cattle by downloading and reading the Oklahoma State University Extension Circular E-861 Vitamin and Mineral Nutrition of Grazing Cattle.