Have you ever had a situation shortly after turning out the cows to grass, when you drive out to the pasture to check cows and there is a cow off by herself that seems restless? You drive over to check on her and she seems a little off, then you honk the horn at her and she comes unglued! While there are cows out there where this could be their normal behavior, there could be something wrong with her. There are multiple diseases but one of the things to keep in mind, when it is cool and wet weather can be the ideal precursor to setting up a perfect storm for grass tetany after it warms up, the grass turns green and is quickly growing. So, what is grass tetany?
Grass tetany is also referred to as hypomagnesemic tetany, spring tetany, grass staggers, or lactation tetany. Grass tetany occurs when the level of magnesium falls below a critical threshold in the blood also known as hypomagnesemia. Cattle and sheep must continually consume magnesium to keep the adequate levels they need, as their body does not mobilize or pull magnesium from tissues. Grass tetany is a serious metabolic disorder which affects grazing animals when there is not enough magnesium available for the animal in the diet. Grass tetany most often affects beef cows which have recently calved and are out grazing lush pastures. The most common scenario is in the spring when the grass is rapidly growing and the lush pastures are high in potassium and protein but low in magnesium and sodium. Cows usually affected are in the early stage of lactation (within the first three weeks of calving) which are high-producing while nursing a calf are at greatest risk. Ewes grazing on pasture nursing more than one lamb may also be affected and tend to also be low in calcium as well. Ewes are usually within the second to fourth week post-lambing. There can be a wide range of incidence from farm to farm, however in extreme situations 20% of the herd or flock may be affected. Death losses of 2% to 3% are commonly observed in a herd, however if not treated promptly can a mortality rate of 30% or more. The onset of grass tetany is rapid and may result in death in as little as six hours after the initial signs become visible to you or I. Which at times it is common to not seen any signs of a sick animal or animals, however to unfortunately find a dead cow. The clinical signs in affected cows depends on the severity of the hypomagnesemia. Borderline low levels of magnesium are not visible, nor life-threatening however due to poor performance have more an economic consequence. Sign to look for with moderate hypomagnesemia are decreased appetite, nervousness, and reduced milk production. As the disease progresses the magnesium falls lower you may also notice muscles twitching of the face, shoulders and flank. Affected cows will become restless and irritable, and may separate themselves from the rest of the herd. Other signs may include: spastic and stiff-legged movements or gait, and frequent urination. A cow may be vocal (or bellowing) and some will become aggressive and sensitive to sound or stimulation. Something as little as honking the horn or chasing the cow often will initiate the appearance of grass tetany in cows with a more moderate hypomagnesemia.
With the cool spring we have been having the cattle will be at risk for grass tetany. We have multiple options of supplements available for cattle on pasture to provide the cattle with adequate magnesium to prevent grass tetany. Contact me or nutrition consultant for more information on magnesium supplement options for your herd.
Thank you and have a safe spring!
Livestock Nutrition Specialist
New Salem & Elgin
Goff, J. Food Animal Practice. Ruminant Hypomagnesemic Tetanies. P 137-140.