Magnesium tetany

Question 1

What is Mg tetany

Answer 1

Grass tetany, grass staggers, winter tetany, Magnesium deficiency
Ruminant livestock – beef cattle, dairy cattle, sheep
Grazing on pastures of rapidly growing grass, esp in early spring – seasonally low Mg conc in forage
Mg deficiency= low intake, absorption, retention or combo

Question 2

Pathogenesis (Mg tetany)

Answer 2

Graze on lush grass pastures or green cereal crops or pastures of rapidly growing grass, esp in early spring – seasonally low Mg conc in forage> Low intake, absorption, retention or combo> Apparent symptoms only develop when hypomagnesemia accompanied by hypocalcemia (serum ca <8)
Mg low in grasses grown on leached acid sandy soils
Can occur in lactating beef cows fed silage indoors.
Low when potash and nitrogen fertilizers are used and growth is vigorous
High levels trans-aconitate can be a risk factor for hypomagnesemia + Mg absorp from rumen may be reduced when K and N intakes are high and Na and P intakes are low
High moisture content in grass causes rapid gut transit and low uptake> reduced absorption of Mg resulting from high rumen K and Nitrogen and low rumen Na
Low energy intake, fasting, sudden changes in feed, Bad weather, esp winter storms, Stress , Low roughage intake, Low intake of P and salt
Adult lactating animals most susceptible bc of loss of Mg in milk

Question 3

Clinical signs (Mg tetany)

Answer 3

Grazing away from the herd, irritability, muscle twitching, staring, incoordination, staggering, collapse, thrashing, coma, death, hyperexcitability, muscle spasms, convulsions, respiratory distress
Acute: suddenly throw up heads, bellow, gallop in blind frenzy, fall, paddling convulsions, death usually within a few hours
Less severe: Ill, walks stiff, hypersensitive to touch and sound, urinates frequently, progress to acute convulsive stage after period as long as 2 – 3 days.
Hypomagnesemia: tachycardia, loud heart sounds are characteristic
Hypomagnesemic tetany occurs in 2 – 4 mo calves being fed milk only or in younger calves with chronic scours while being fed milk replacer – hyperexcitability, muscle spasms, convulsions, death

Question 4

Diagnosis (Mg tetany)

Answer 4

Confirmed by response to tx, confirmation of hypomagnesemia in samples taken before tx (Mg plasma < 1.2mg/dl in cattle <0.8 in sheep)

Question 5

Treatment (Mg tetany)

Answer 5

Tx: Combined solutions of Ca and Mg, preferably slow IV while monitoring heart
Response to tx slower in animals with low mg tetany than in animals with hypocalcemia alone bc of time it takes to restore Mg in CSF
Animal should not be stimulated during tx – could trigger fatal covulsions
Additional Mg sulfate can be given SQ
After tx – cows left to respond without stim and then moved off the tetany prone pasture if possible
Must have hay tx with 2 oz of Mg oxide daily – otherwise condition can recur within 36 h after therapy

Question 6

Prevention (Mg tetany)

Answer 6

Mg must be given daily to animals at risk – body has no stores – lost in urine feces, milk - Daily oral supplementation of Mg oxide given in danger period, Most Mg salts unpalatable – must be combined with molasses, concentrates, hay
Feeding hay alone might be enough in herds where only old cows (>6y) are affected- Sheep and cattle should have access to hay particularly when grazing either green cereal crops or pastures fertilized with K or Nitrogen. Mg absorption efficiently in calves fed milk falls from 87% at 2 – 3 weeks to 32% at 7 – 8 weeks
If slow release intraruminal mg devices administered – animals also should be provided with hay
Fertilizers containing Mg effectively increase herbage Mg only on certain soil types
Out-wintered stock should be protected from wind and cold and provided with supplementary food