Magnesium is a major mineral essential for the health and productivity of sheep, serving as a component in numerous biological processes. The sheep’s body has a limited capacity to store magnesium, requiring a consistent, daily dietary intake for survival. This lack of internal reserve makes sheep particularly susceptible to rapid depletion and deficiency. Maintaining the proper balance of this macro-mineral is foundational to sheep husbandry, influencing flock well-being and mitigating the risk of the severe metabolic disorder known as Hypomagnesemia.
Essential Physiological Functions and Requirements
Magnesium is a cofactor for hundreds of enzyme systems, playing a direct role in energy generation and metabolism. It is central to oxidative phosphorylation and glycolysis, the pathways for producing cellular energy. This mineral is also necessary for maintaining normal neuromuscular function, regulating nerve impulses and controlling muscle contractions.
About 70% of the body’s magnesium is found in the skeleton, contributing to bone structure. However, only a small fraction of this skeletal magnesium can be mobilized quickly to buffer sudden drops in blood levels. Due to this limited mobilization capability, sheep must absorb magnesium from the rumen daily to satisfy needs for circulation and soft tissue function. The general dietary requirement for maintenance ranges from 0.12% to 0.18% of the diet dry matter. This requirement increases significantly for lactating ewes, whose need can double or triple due to the substantial loss of the mineral in milk.
Understanding Hypomagnesemia in Sheep
Hypomagnesemia, commonly referred to as Grass Tetany or Grass Staggers, is a severe neurological condition triggered by low blood magnesium levels. Symptoms relate directly to the mineral’s role in nerve and muscle control. Initial signs include facial muscle twitching, a stiff-legged, uncoordinated gait, and general restlessness.
As the deficiency progresses, affected sheep become hypersensitive to touch and sound, leading to staggering, collapse, and involuntary muscle contractions known as tetanic spasms. The animal may lie on its side with its legs rigidly extended. Without immediate treatment, death can follow quickly, often within hours. Sudden mortality is frequently the first indication of a problem within the flock.
Hypomagnesemia is a high-risk condition, particularly in spring. Grazing on lush, fast-growing pasture is a primary trigger because young grass often has naturally low magnesium content. These grasses are frequently high in potassium and nitrogen, which actively interfere with magnesium absorption from the rumen. Lactating ewes are the most vulnerable group, with peak risk occurring four to six weeks after lambing. Stressors like cold, wet weather or sudden changes in feed intake also predispose ewes to the condition.
Practical Magnesium Supplementation Strategies
Preventing Hypomagnesemia requires ensuring a consistent, adequate intake of magnesium, especially during high-risk periods like early lactation.
Supplementation Methods
One common preventative measure is the use of magnesium-fortified mineral blocks or loose licks, which typically contain magnesium oxide (Causmag). These supplements are effective only if the sheep consume them regularly, with target intakes for lactating ewes often set around 20 to 30 grams per day.
Another strategy involves dusting pastures with calcined magnesite or a similar magnesium compound before grazing begins. This method ensures that the sheep ingest the mineral directly with the grass, bypassing issues of palatability or selective consumption. For long-term prevention, farmers can also utilize slow-release magnesium boluses, which are administered orally and reside in the rumen.
Magnesium can also be added to feed concentrates or drinking water, though consumption consistency can vary.
Emergency Treatment
For an animal exhibiting the acute symptoms of Grass Tetany, emergency intervention is necessary. This involves the rapid administration of a magnesium solution, typically delivered as a subcutaneous injection of magnesium sulfate, sometimes combined with calcium, to quickly raise blood plasma levels. Veterinary consultation is advised for the proper acute treatment and follow-up care.