Bovis ISSN 2398-2993

Hypomagnesemia

Synonym(s): Staggers, Grass staggers, Grass tetany

Contributor(s): Seamus O'Shea , Keith Cutler

Introduction

  • Cause: low blood magnesium (Mg) levels, as a result of inadequate dietary magnesium intake or poor absorption from the gut.
  • Signs: hyperesthesia, ataxia, seizures, sudden death.
  • Diagnosis: blood magnesium levels.
    • Definition: serum ionized magnesium <1.5mg/dL or <0.65mmol/L.
  • Treatment: intravenous and subcutaneous magnesium/calcium preparation.
    • This is a true emergency and treatment must be initiated ASAP.
    • Treatment goes beyond stabilising the individual cow.
      • These cases are often the tip of the iceberg and a herd approach will be necessary.
    • Less experienced clinicians would be encouraged to seek the assistance of their senior colleagues when advising farmers as to herd management of these cases.
  • Prognosis: variable. Dependent upon early intervention and treatment.
Print off the farmer factsheet on Staggers to give to your clients.

Pathogenesis

Etiology

  • Insufficient dietary Mg Magnesium: an overview - fails to meet maintenance requirements, growth requirements or lactational requirements.

Predisposing factors

General

  • Lush pasture: especially spring growth - fast growing.
  • Lactating cattle: due to Mg loss in milk. 
  • Fast growing calves: due to increased Mg demand.
  • Exposure to extreme weather (reduced food intake and increased stresses).
  • Beef cattle and dry cows predisposed if left to overwinter out at pasture with no supplementation.

Specific

  •  Most commonly seen around the time of calving.
  •  High levels of Potassium Sodium and potassium - an overview (in soil) and Nitrogen (from fertilizer)- reduces Mg available for uptake by the cow.

Pathophysiology

  • Magnesium Magnesium homeostasis is an essential cation involved in many intracellular enzymatic reactions, including regulating the calcium channel function, neurotransmission, vasomotor tone, muscular contraction and cardiac excitability. 
  • Magnesium is primarily an intracellular cation, with only 1% being found in the serum.
    • Intracellular magnesium is primarily in the bone (67%), muscle (2%) and other soft tissues (11%).
    • Extracellular magnesium exists in three forms:
      • Protein-bound.
      • Complexed with anions (such as phosphate).
      • Ionized.
        • Ionized magnesium is the physiologically active form.
  • Total serum levels therefore may not reflect either the active moiety or the total body concentration.
  • Magnesium is antagonistic to the actions of calcium Calcium and phosphorous - an overview.
  •  A significant role for intracellular magnesium is as a co-factor for the calcium-ATP pump that moves intracellular calcium into the sacroplasmic reticulum.
    • It performs a similar role with the sodium-potassium-ATP pump that moves these electrolytes across cell membranes.
    • Reduction of the activity of these ion pumps is likely to be the major cause of the clinical signs of hypomagnesemia.
  • Magnesium’s role in active transport of Ca and K ions across cell membranes plays an important role in the process of nerve impulse conduction. This in turn affects muscle contraction and cardiac muscle activity.
    • This altered skeletal and cardiac muscle function leads to the symptoms of ataxia, muscle weakness and dysrhythmias Dysrhythmias.
    • If not corrected can progress to death.

Timecourse

  •  Acute form: sudden death.
  •  Sub-acute form: may persist for days.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Allcroft R & Burns K (2011) Hypomagnesaemia in Cattle.  New Zealand Veterinary Journal 16 (7).


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