Adult cattle and sheep have no effective tissue stores of magnesium, so lactating animals are at risk of developing a deficiency. The risk is increased when they are grazing pasture, especially in Spring and Autumn when the absorption of magnesium is influenced by factors including: high levels of potassium, nitrogen and moisture content and low levels of sodium. Magnesium requirements are influenced by production. Therefore rapidly-growing and lactating animals have a higher requirement than non-lactating slow-growing animals. Cows in their third to fifth lactation have an increased risk of developing hypomagnesaemia due to increased production and reduced age-related mobilisation of magnesium from bone. Ruminants may survive for a few days by using residual magnesium in their soft tissues, but other than this, they cannot store magnesium effectively.
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Adult lactating animals are most susceptible because of the loss of Mg in milk. Hypomagnesemic tetany occurs mainly when animals are grazed on lush grass pastures or green cereal crops but can occur in lactating beef cows fed silage indoors.
It is rare in nonlactating cattle but has occurred when undernourished cattle were introduced to green cereal crops. Mg absorption from the rumen may be reduced when potassium and nitrogen intakes are high and sodium and phosphorus intakes are low. Soils naturally high in potassium and those fertilized with potash and nitrogen are high-risk areas for hypomagnesemic tetany.
The more complex mineral interactions are likely to be involved in herds in which hypomagnesemic tetany occurs in first- and second-calving cows as well as in older cows. The hypocalcemia arises from either a reduction in calcium intake or absorption, or both.
Urine Mg concentrations are a useful guide to Mg status and are undetectable in cows with hypomagnesemia. In the most acute form, affected cows, which may appear to be grazing normally, suddenly throw up their heads, bellow, gallop in a blind frenzy, fall, and exhibit severe paddling convulsions. These convulsive episodes may be repeated at short intervals, and death usually occurs within a few hours. In many instances, animals at pasture are found dead without observed illness, but an indication that the animal had convulsions before death may be seen from marks on the ground.
In less severe cases, the cow is obviously ill at ease, walks stiffly, is hypersensitive to touch and sound, urinates frequently, and may progress to the acute convulsive stage after a period as long as 2—3 days.
This period may be shortened if the cow is transported or driven to a fresh pasture. When animals have hypocalcemia and hypomagnesemia, the signs shown depend on which predominates.
With hypomagnesemia, tachycardia and loud heart sounds are characteristic signs. The disease in lactating ewes occurs under essentially the same conditions and has the same clinical signs as in cattle. Diagnosis is usually confirmed by response to treatment, followed by confirmation of hypomagnesemia in samples taken before treatment. Urine Mg is usually undetectable in cows with hypomagnesemic tetany. Animals showing clinical signs require treatment immediately with combined solutions of calcium and Mg, preferably given slowly IV while monitoring the heart see Parturient Paresis in Cows.
The response to treatment is slower in animals with hypomagnesemic tetany than in animals with hypocalcemia alone, because of the time it takes to restore Mg in the CSF. The animal should not be stimulated during treatment, because this could trigger fatal convulsions.
After treatment, cows should be left to respond without stimulation and then moved off the tetany-prone pasture, if possible.
Animals must be provided with hay treated with 2 oz 60 g of Mg oxide daily; if this is not done, the condition can recur within 36 hr after initial therapy. Mg must be given daily to animals at risk, because the body has no readily available stores.
Most Mg salts are unpalatable and must be combined with other palatable ingredients such as molasses, concentrates, or hay. Fertilizers containing Mg effectively increase herbage Mg only on certain soil types. If rainfall exceeds 40—50 mm within 2—3 days of dusting, the herbage will require another dusting.
Out-wintered stock should be protected from wind and cold and provided with supplementary food. Sheep and cattle should have access to hay, particularly when grazing either green cereal crops or pastures fertilized with potassium or nitrogen or both.
Hypomagnesemic tetany occurs in 2- to 4-mo-old calves being fed milk only, or in younger calves with chronic scours while being fed milk replacer.
Clinical signs are similar to those of hypomagnesemic tetany in adult cattle see above and include hyperexcitability, muscular spasms, convulsions, and death. Hypomagnesemic tetany in calves must be differentiated from acute lead poisoning see Lead Poisoning , tetanus see Tetanus , strychnine poisoning see Strychnine Poisoning , polioencephalomalacia see Polioencephalomalacia , and enterotoxemia caused by the toxin of Clostridium perfringens see Enterotoxemias.
Provision of good-quality legume hay and a starter ration from 2 wk of age prevents the disorder. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Veterinary Manual was first published in as a service to the community.
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Common Veterinary Topics. Videos Figures Images Quizzes. Clinical Findings:. Hypomagnesemic Tetany in Calves. Disorders of Magnesium Metabolism. Test your knowledge.
All animals absorb potassium through the gastrointestinal tract and then excrete it through the kidneys. Adult ruminants also secrete potassium through their saliva. Which of the following hormones plays a key role in the excretion of potassium in animals?
More Content. Was This Page Helpful? Yes No. Magnesium as an Equine Dietary Supplement. Overview of Transport Tetany in Ruminants. Nutritional Requirements of Beef Cattle. Nutrition and Disease in Dairy Cattle. Ketosis in Cattle. Add to Any Platform.
Hypomagnesemic Tetany in Cattle and Sheep
Ricardo A. Costa 3. An outbreak of hypomagnesemia is reported in Holstein dairy cattle grazing lush oat Avena sativa pasture in Uruguay. Nine of 3. These nine cows were from 2 to 9-years-old 1st-6th lactation , with 22 to days of lactation and
Grass tetany (Hypomagnesemia) in beef cattle
Adult lactating animals are most susceptible because of the loss of Mg in milk. Hypomagnesemic tetany occurs mainly when animals are grazed on lush grass pastures or green cereal crops but can occur in lactating beef cows fed silage indoors. It is rare in nonlactating cattle but has occurred when undernourished cattle were introduced to green cereal crops. Mg absorption from the rumen may be reduced when potassium and nitrogen intakes are high and sodium and phosphorus intakes are low.