BEEF HERD HEALTH BY W. MARK HILTON, DVM Grass tetany, also known as hypomagnesemia, is a metabolic disorder caused by low magnesium levels in cattle. We generally see this disease in two classes of cows and in one of two nutritional situations. The most common scenario is in early lactation beef cows grazing lush, fast-growing pastures in early spring. We can also see the grass tetany when these cows are consuming primarily grass hay before pasture turnout. Grass tetany (or sometimes referred to as “winter tetany”) can also occur in late gestation cows when they are either grazing these early spring pastures or eating grass hay. Preventing grass tetany involves several key strategies: 1. Provide magnesium supplementation: - Ensure cows consume 4 ounces/head/day of a high magnesium (Hi Mag) mineral containing 10-15 percent magnesium. If cows are grazing pasture, the loose, salt-hi mag mineral mix can be fed free choice. To be sure the cows are consuming the amount listed on the label, weigh out the mineral and calculate consumption. A 50# bag should last 50 cows four days (4 ounces (or ¼ pound) x 4 days x 50 cows = 50#) while a herd of 25 cows would take eight days to clean it up. If cows are overconsuming or under consuming, contact your feed supplier for assistance in rectifying the issue. - If cows are consuming feed in a bunk, top dress the loose, salt-hi mag mineral mix on the feed to ensure all cows receive the proper amount. Studies show that about 15 percent of cows eat either zero or much less mineral than required when it is fed free choice, so any time you are feeding a feedstuff, top dress the mineral mix on the ration. - While tubs and licks tend to be a more costly source of minerals, consumption can be improved over loose salt-mineral mixes because many are molasses based. If grass tetany is a problem on your farm, using these molasses-based products that contain a higher level of magnesium may be a good option when you are unable to supplement a feedstuff high in magnesium. 2. Manage pasture composition: - Avoid grazing lush, rapidly growing, cool season grasses which are often low in magnesium. Grass tetany is most likely to occur when cows are grazing small grain pastures like wheat, rye and triticale. These pastures would be best utilized by heifers that are being kept for replacements or fall calving cows. - Mix legumes (e.g., clover, alfalfa) into pastures, as they have higher magnesium content than grasses. - Limit nitrogen and potassium fertilization, as excessive levels can reduce magnesium uptake in forage. High potassium soils and high potassium feedstuffs are the biggest risk factors in causing grass tetany. 3. Provide supplemental feed: - Feed a feedstuff like wet or dried distiller’s grains with solubles (DDGS) or alfalfa hay that is high in magnesium. Work with your nutritionist to determine how much to feed per day. - Feed cows dry hay before turning them out onto lush pastures to slow down digestion and improve magnesium absorption. - Avoid sudden dietary changes that could disrupt magnesium balance. 4. Ensure adequate energy and mineral balance: - Maintain proper calcium, phosphorus, and sodium (salt) levels in the diet, as imbalances can exacerbate magnesium deficiency. - Monitor body condition scores (BCS) to ensure cows are not undernourished, as thin cows are more susceptible. 5. Monitor high-risk cattle - Older, high-milking cows are most at risk and require closer observation. - Cold, wet weather and stress (transportation, changes in diet) increase susceptibility. The “perfect storm” for grass tetany is when the weather warms up, the cows are turned out on a cool season grass or small grain pasture and then the weather turns colder. The colder weather increases consumption of the low magnesium/high potassium forage and down goes the cow into a state of tetany. - Watch for early symptoms (nervousness, muscle twitching, unsteady gait) and be prepared to call your herd health veterinarian quickly so IV treatment can be initiated. By implementing these prevention strategies, you can significantly reduce the risk of grass tetany in your beef cows. |
