Dr. Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist, offers herd health advice as part of the weekly series known as the "Cow Calf Corner" published electronically by Dr. Peel and Dr. Glenn Selk. Today, Dr. Selk explains how feeding mineral can reduce the risk of grass tetany in your cattle herd, next spring.
"Much of Oklahoma and the Southern Plains will 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.
"Grass tetany, caused by magnesium deficiency does not seem to be a major problem in Oklahoma although occasional cases are reported. It 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. Grass tetany most frequently occurs when cattle are grazing lush immature grasses or small grains pastures and tends to be more prevalent during periods of cloudy weather. Symptoms include incoordination, salivation, excitability (aggressive behavior towards 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 have also 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. It is likely that a combination of factors, all related to characteristics of lush forage are involved.
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