Special to The Eagle: "Ask the Vet" column for February 2008
Q -- I'm new to this area and was surprised when my coffee-drinking buddies down at the cafe told me I should start feeding special minerals to my cows in February to prevent a disease called grass tetany. I'm not familiar with that problem. Would you please tell me what I should know about the disease?
A -- Grass tetany is a nutritional disease of cattle caused by inadequate dietary magnesium. The condition is most commonly called grass tetany, but has more names than a liter of Texas Blue Laceys. Ingestion of inadequate amounts of magnesium results in below normal concentrations of magnesium in the blood of cattle -- hypomagnesemic tetany. Affected animals become excitable, belligerent, have muscular twitches, fall down and go into convulsions. It is most common in lactating beef cows -- lactation tetany.
In the Brazos valley, we see cases of grass tetany starting as early as February in lactating beef cows grazing young spring pastures. Lactating beef cows require a diet of 0.22 percent magnesium (Mg) while rapidly growing spring grasses commonly contain 0.10 to 0.12 percent Mg -- grass tetany. Magnesium deficiency also results when cattle graze young spring grass with adequate Mg concentrations, but low sodium (Na) and high potassium (K) or nitrogen (N) concentrations. Sodium deficiency results in an increase in K in saliva and the rumen. High concentrations of K reduce Mg absorption in the digestive tract. Nitrogen which is present in high concentrations in rapidly growing grass also interferes with Mg absorption. Thus, risk of grass tetany is especially high when pastures are heavily fertilized with nitrogen and/or potassium.
I have also seen an outbreak of grass tetany in January in a group of beef cows that were fed bermudagrass hay containing only 0.11 percent magnesium. Wheat hay or pasture is often associated with magnesium deficiency because wheat contains very low concentrations of magnesium, commonly around 0.12 percent -- wheat pasture poisoning.
There are many other factors that influence the occurrence of grass tetany:
JThin cows on low-energy diets are more susceptible than cows in good body condition. Energy intake affects absorption of Mg in a positive manner.
JOld cows are more susceptible than young cows.
JBrahman and Brahman-cross cattle are less susceptible than non-Brahman cattle.
JWinter storms sometimes precipitate an outbreak of grass tetany because during a storm feed consumption decreases and urinary excretion of magnesium may increase -- snow tetany or winter tetany. Magnesium is not readily released from bones of adult cattle. Thus, lactating beef cows must ingest 20 grams of magnesium every day to meet their requirement.
Grass tetany is a highly fatal disease. Often a cow is found dead with no warning because death can occur within hours in severe cases. The first sign of illness is a change in behavior to an alert belligerent attitude. Affected cows are nervous and hold their heads high. Their muscles tremble and ears twitch. They may walk with a stiffened gait and stagger -- grass staggers. Then they fall to the ground, thrash about and have seizures of muscle spasms (tetany). If a cow in the early stages is stressed, she will often rapidly become more aggressive, collapse, develop convulsions and die.
Immediately call your veterinarian if you find a cow with these clinical signs. This is an emergency of the highest urgency. Treatment must be given promptly with a minimal amount of excitement. Cows affected in the pasture often die from the stress of being caught and restrained.
Treatment consists of intravenous and subcutaneous administration of solutions containing Mg and calcium followed by oral supplementation with Mg paste for several days. Improper intravenous administration of magnesium solutions can cause death due to heart irregularities. Thus, treatments must be given by an experienced veterinarian.
There are several management practices that can reduce the chance of an outbreak of grass tetany. The most common is to offer cows a commercial salt/trace mineral mixture containing around 10 percent magnesium oxide. Mineral mixtures designed to prevent grass tetany usually are labeled Hi-Magnesium or Green Pasture minerals. It's very important the product is the only source of minerals in the pasture. Unfortunately, consumption is often inadequate because magnesium oxide is bitter. Cottonseed meal (CSM) or molasses can be mixed with the mineral to increase palatability. The ratio of CSM to mineral needed to obtain recommended amounts of consumption (usually 4 ounces per head per day) varies from one ranch to another and often must be found by trial and error. Ten pounds of CSM per 100 lbs. of mineral often boosts consumption to desired levels.
Feeding legumes which naturally contain high concentrations of Mg will also prevent grass tetany. Cattle can be supplemented with legumes by feeding alfalfa hay or by overseeding pastures with clover. Feeding 10 pounds of alfalfa hay per cow per day will promptly stop an outbreak of grass tetany.
Other methods of prevention include dusting pastures with Mg, injecting round bales with Mg solutions, or spraying a solution of Mg and molasses onto hay in windrows as the hay is baled. It is also important to not overfertilize pastures with K and N. Fertilization should be based on periodic soil analysis to insure application of a balance of K, N and Mg that results in optimum grass production with minimum danger of grass tetany.
Grass tetany is a fatal disease of lactating beef cows that strikes every spring in the Brazos valley. The most practical prevention is to put out a high-magnesium salt/trace mineral supplement just before rapid growth of spring pasture. Looks like this is just about the perfect time to visit your feed store and bring that special high-Mg mineral home to your cows.
Share this story:
Google
Yahoo
digg
del.icio.us
facebook
Slashdot
