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Grass tetany is a
metabolic disease A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients, such as proteins, fats, and carbohydrates. Metabolic disorders can happen when abnormal chemical reactions in the body alter the ...
involving magnesium deficiency, which can occur in such ruminant livestock as
beef cattle Beef cattle are cattle raised for meat production (as distinguished from dairy cattle, used for milk production). The meat of mature or almost mature cattle is mostly known as beef. In beef production there are three main stages: cow-calf operat ...
,
dairy cattle Dairy cattle (also called dairy cows) are cattle bred for the ability to produce large quantities of milk, from which dairy products are made. Dairy cattle generally are of the species ''Bos taurus''. Historically, little distinction was mad ...
and sheep, usually after grazing on pastures of rapidly growing
grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...
, especially in early
spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...
.


Symptoms and cause

Progressive symptoms may include grazing away from the herd, irritability, muscle twitching, staring, incoordination, staggering, collapse, thrashing, head thrown back, and coma, followed by death. However, clinical signs are not always evident before the animal is found dead. The condition results from hypomagnesemia (low magnesium concentration in blood) which may reflect low magnesium intake, low magnesium absorption, unusually low retention of magnesium, or a combination of these. Commonly, apparent symptoms develop only when hypomagnesemia is accompanied by hypocalcemia (blood Ca below 8 mg/dL). Low magnesium intake by grazing ruminants may occur especially with some grass species early in the growing season, due to seasonally low magnesium concentrations in forage dry matter. Some conserved forages are also low in magnesium and may be conducive to hypomagnesemia. High potassium intake relative to calcium and magnesium intake may induce hypomagnesemia. A K/(Ca+Mg) charge ratio exceeding 2.2 in forages has been commonly considered a risk factor for grass tetany. Potassium fertilizer application to increase forage production may contribute to an increased K/(Ca+Mg) ratio in forage plants, not only by adding potassium to soil, but also by displacing soil-adsorbed calcium and magnesium by ion exchange, contributing to increased susceptibility of calcium and magnesium to leaching loss from the root zone during rainy seasons. In ruminants, high potassium intake results in decreased absorption of magnesium from the digestive tract. Trans-aconitate, which accumulates in some grasses, can be a risk factor for hypomagnesemia in grazing ruminants. (Tetany has been induced in cattle by administration of trans-aconitate and KCl, where the amount of KCl used was, by itself, insufficient to induce tetany.) Relatively high levels of trans-aconitate have been found in several forage species on rangeland sites conducive to hypomagnesemia. Although at least one rumen organism converts trans-aconitate to acetate, other rumen organisms convert trans-aconitate to tricarballylate, which complexes with magnesium. Using rats as an animal model, oral administration of tricarballylate has been shown to reduce an animal's magnesium retention. Potassium fertilizer application results in increased concentration of aconitic acid in some grass species.


Prevention

Magnesium supplements are used to prevent the disease when ruminants, for obvious economic reasons, must have access to dangerous pastures.


Treatment

The affected animal should be left in the pasture, and not forced to come back to stall because excitation can darken the prognosis, even after adequate treatment. Intravenous mixed calcium and magnesium injection are used. Subcutaneous injection of
magnesium sulfate Magnesium sulfate or magnesium sulphate (in English-speaking countries other than the US) is a chemical compound, a salt with the formula , consisting of magnesium cations (20.19% by mass) and sulfate anions . It is a white crystalline solid, s ...
(200 ml of 50% solution) is also recommended.


Epidemiology

In Northern Europe, the disease occurs after winter housing. But in Australia and New Zealand, where the cows are not housed, the disease occurs in similar conditions, when the animal enters lush, grass-dominant pastures. In North America, grass tetany occurs most commonly when range stock are moved onto lush early pasture or when housed stock are turned out onto such pasture in the spring. A second high-risk period may occur in the fall. Although cereal grasses (e.g. winter wheat) and crested wheatgrass may be especially conducive to grass tetany, the problem can also occur with several other grass species. "Winter tetany" may occur with some silages,Kahn, M. A. (ed.) 2005. Merck veterinary manual. 9th Ed. Merck & Co., Inc., Whitehouse Station. low-magnesium grass hays, or
corn stover Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maĆ­z after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
.Allison, C. 2003. Controlling grass tetany in livestock. New Mexico State Univ. Coop. Ext. Serv. Guide B-809. http://aces.nmsu.edu/pubs/_b/B-809.pdf


References


External links

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Related page of the Merck Veterinary Manual
Bovine diseases