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Grass Tetany and Acorn Poisoning could Cause Problems this fall

Livestock Update, October 2001

John B. Hall, Extension Animal Scientist, Beef, VA Tech

Many area of the state are dry after the lack of rain in August and September. If we get the much wished and prayed for rains this fall, grass tetany could be as much a fall problem as a spring one this year. The lush growth of grass during wet falls after at drought is similar in mineral content to spring grass. High levels of fertilization to encourage growth of much needed grass could make the problem worse.

Remember grass tetany is a magnesium deficiency that primarily effects lactating cows. Fall calving cows are at the greatest risk. There is little problem with dry cows. Cows should be supplemented with a mineral containing 12-14% magnesium. Cows on poultry litter diets should get 2 ounces of magnesium oxide per animal each day because litter is extremely low in magnesium.

As pasture availability decreases, cattle are moving to any place there is something to eat. Cattle will often head for woods and wooded lots around the farm in search of grazing or browse. However, that could be dangerous. Green acorns are plentiful this year. Hungry cattle love acorns that can quickly poison them. Green and ripe acorns contain gallotannins, which cause kidney damage and death. There does not seem to be as great a problem after a few hard freezes. The reduced palatability of acorns after weathering may be part of the answer.

To prevent acorn poisoning, cattle should be provided with supplemental feed and fenced out of areas with large amounts of oak trees until this winter. There are few other options as only a few pounds of acorns can cause enough damage to kill cattle. Outward signs of acorn poisoning are few but include weight loss and diarrhea, but often these are not noticed until other cattle in the herd have died.

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