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Food Animal Medicine > Hypomagnesemia > Flashcards

Hypomagnesemia Flashcards

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1
Q

What is magnesium’s role in the body? how much should a cow have?

A
  • Cofactor for enzymatic reactions in every metabolic pathway
    • nerve conduction
    • muscle function
    • bone formation
  • Distribution (600kg cow)
    • Intracellular = 84 g
    • Extracellular = 3g
      • Blood = 0.84g
    • Bone mineral = 210g
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2
Q

Where is Magnesium absorbed from?

A
  • The forestomachs (primarily rumen)
    • No compensation by the SI or LI if the rumen does not get the job done
  • Minimum oral intake is necessary for net absorption
    • (5.4g/d cattle)
  • Mg uptake is mainly driven by a small chemical gradient and a large electrical potential difference
    • Different mechanisms of absorption help maintian net uptake and continuous inflow with varied intra-ruminal Mg concentrations
      • High K and Ammonia/ammonium will reduce Mg absorption by electrochemical gradient
      • High levels of Ionized Mg will stimulate Mg absorption via its concentration gradient
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3
Q

What are the Positive influences on Magnesium Absorption?

A
  • Supplementation with mineral
  • Rumen pH <6.5
  • High grain diets
  • Ionophores
    • Improved Na-linked transport
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4
Q

What are the negative influences on magnesium absorption?

A
  • Low Mg content of forages
  • Rumen pH >6.5
  • Grazing - salivary buffer
  • Organic compounds in forages
    • formulation of insoluble Mg salts
  • Lush, high moisture grasses
    • decreased transit time
  • High dietary K and ammonia/ammonium
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5
Q

What hormones influence Mg?

A
  • Secondary influence:
    • PTH
    • ALdosterone
    • Vit D
    • etc
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6
Q

What stimulates Mg flux from ECF pool to tissue?

A
  • Transport exertion
  • Insulin, epinephrine, norepinephrine - likely cause an intracellular influx
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7
Q

What basic functions is Mg involved in

A
  • Required in ATP formation and use
  • Hormone activation via cAMP (adenyl cyclase)
  • Ach esterase (Mg Deficience = ⇡Ac)
  • CNS/myoneural junctions
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8
Q

What are the different Mg Deficiency diseases?

A
  • Grass Tetany:
    • Spring/Fall (cool season grasses)
    • Rapid growth
  • Wheat pasture poisoning
    • Winter wheat grazed by cattle
    • Other cereal crop pastures (Rye, Oats, etc)
  • Lactation tetany
    • lactating cows
  • Winter tetany:
    • Most feed for beef cows in winter are deficient
    • Harvested during spring or fall (low Mg)
    • Poor digestablity
  • Milk tetany
    • calves fed milk only become deficient after 6 weeks because GI tract becomes less efficient in absorption of Mg
  • Transport Tetany
    • Cattle on marginal diets are transported
    • Stress of transport, lack of feed intake
    • Confinement of cattle for processing
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9
Q

What are the Clinical signs of hypomagnesemia?

A
  • Anorexia (acute)
  • Alert, hyperexcitable or comatose
  • Ears twitch, muscle fasiculaitons, tremors
  • belligerent, bellowing, running
  • Incoordination, recumbency
  • Pyrexia (muscle contractions_
  • Elevated respiratory rates
  • Convulsions, seizures, opithotonus
  • Tachycardia ~150bpm
  • Tachypnea ~60resp/min
  • fever up to 105
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10
Q

What are the differentials for Hypomagnesemia?

A
  • Rabies
  • Nervous ketosis
    • dairy cows
  • Bovine spongiform encephalopathy
  • Downer cow syndrome
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11
Q

What clinical pathology is associated with hypomagnesemia?

A
  • Normal serum Mg: 1.7-3.3 mg/dL
    • <0.8 is associated with clinical signs
    • Some clinical animals have normal serum Mg
  • CSF Mg usually mirrors serum Mg
    • <1mg/dL = convulsions
    • Reliable up to 24hrs post mortem
  • Urine Mg
    • Decreased urine Mg output when deficient
    • Normal >4.4 mM
    • 1-4.4mM ⇢ likely Mg insufficiency
    • <1mM likely to be clinical deficiency
  • Serum Calcium
    • low to normal
    • Hypocalcemia may relate to Mg requirement of PTH action
  • Serum K
    • often elevated
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12
Q

what samples can be taken post-mortem to test for magnesium levels?

A
  • CSF
  • Vitreous humor - good for 48hrs on ice
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13
Q

What is the Treatment for hypomagnesemia?

A
  • IV solution of Mg salts
    • Mg Hypophosphite
    • Mg sulfate
    • Mg Lactate
    • Calcium salts
  • Emergency
    • Recumbent/convulsing
      • IV may not be safe
      • Rectal suppository
      • Relapse
      • Prognosis guarded
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14
Q

How can Hypomagnesemia be prevented?

A
  • Feed 60 gm/hg/day maintenance
  • Feed daily when clinical signs have arisen (additional 15-30mg/d)
  • Salt free choice (increase sodium intake)
  • 100lb/ton protein supplement
  • 0.5% in dairy ration
  • Dust pastures with MgO
    • 25lbs/acre
  • Soil treatment
    • Limestone (dolomite) 2.5tones/acre
    • MgO 28lbs/acre
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15
Q

What are the general recommendations for avoiding hypomagnesemia in cattle?

A
  • Feed mature grass or legume hay
  • Spray pastures with Mg
  • Add 10lb MgSO4 to 500gal water trough
  • High Mg blocks/supplements
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16
Q

What are the distribution levels of Phosphorus in the cow?

A
  • 600kg cow
    • Extracellular 5-8g
      • Plasma inorganic P - 1.2-2.2g
    • Intracellular 185g
      • Erythrocytes 5.5-6.5g
    • Bones 4kg
17
Q

What are the body’s demands for phosphorus? (cattle)

A
  • Late gestation 10g/day for fetal skeletal growth
  • Milk production 0.9g/kg of milk (10-70kg/day)
  • Salivary loss - min of 5g/day
  • Urine 2-12g/day
18
Q

What is Fibroblast Growth Factor 23? (FBGF 23)

A
  • Produced in response to elevated P
  • Inhibits 1,25(OH)2D
    • reduces active transport of P across intestinal cells
  • Blocks renal reabsorption of phosphate
    • Increased urinary P excretion
19
Q

What happens to 1,25(OH)2D when phosphorus levels are low?

A
  • Directly stimulated
  • upregulation of intestinal absorption
20
Q

What are the different types of phosphorus deficiency?

A
  • Acute Hypophosphatemia
    • Hypophosphatemia “downer cows”
    • Post-Parturient Hemoglubinuria (PPH)
  • Chronic Hypophosphatemia
    • Rickets/osteomalacia
    • Illthrift - Poor BCS, rough haircoat, pica
21
Q

What is Hypophosphatemia “Downer Cow”

A
  • Suspected when a cow does not respond to hypocalcemia treatment
  • Prolonged decrease in plasma P can occur despite restoring plasma Ca
    • Alert Downer cow syndrome
    • Serum P <0.3mmol/L
  • Can see in Beef cattle
    • late season pasture is inherently low in P
    • late gestation plus questionable P intake lead to signs of acute hypophosphatemia similar to down diary cow. Weak or unable to rise
    • Clinical signs not consistent with hypomagnesemia
22
Q

What is the treatment for Hypophosphatemia “Downer Cow”

A
  • PO 50-60gm P by 200-300g monosodium phosphate drench
  • IV: 6-q2 gm (10-20mg/kg) P by monosodium phosphate dissolved in 1L of saline
23
Q

What is Post parturient hemoglobinuria?

A
  • Glyceraldehyde-3-phosphate of the glycolysis cycle
    • Responsible for producing TP in erythrocytes
    • Require inorganic phosphate as a cofactor
    • Inadequate ATP ⇢ decreased Na-K pump function ⇢ ^ [Na] ⇢ cell rigidity and rupture in capillary beds
  • Occurs up to 6 weeks post partum
  • Intravascular hemolysis, anemia, and hemoglobinuria
24
Q

What is the normal distribution of Potassium in a cow?

A
  • 600kg Cow
    • Intracellular 1150g
    • Extracellular 23g
      • Plasma pool 7.5g
  • Demand
    • Urinary loss 23g
    • Fecal loss 85g
    • Milk production 23g
  • Normal DMI 14kgDM/day
    • 1.5% K = 58g excess K excreted by urine
25
Q

How is Potassium homeostasis maintained in cows?

A
  • Ruminant diets are High in K
  • Aldosterone - promotes renal and salivary secretion of K
  • Insulin - promotes intracellular uptake of K
  • Catecholamines (epinephrine) - drive K intracellularly
  • Acid-Base - move into cells with alkalosis and out of cells with acidosis
26
Q

What are causes of hypokalemia?

A
  • Anorexia
  • Muscle catabolism - protein deficiency
  • Excessive aldosterone secretion
    • Isoflupredone
  • Diuretics
    • Acetazolamide, Thiazide >>furosemide
  • Insulin
    • exogenous >> endogenous
  • Stress
  • Hypochloremia
27
Q

What does potassium have to do with resting membrane potential?

A
  • Ratio of ICF:ECF potassium determines RMP of the cell
    • 150mmol/L : 4.5mmol/L
  • Hypokalemia causes resting membrane potential to be MORE negative (=muscle weakness)
    • Reduced action potentials
    • Reduced Ach release
    • Reduced # of muscle fibers that contract
28
Q

What is Hypokalemia syndrome?

A
  • Profound weakness/recumbency
    • S-curved neck
    • Tachycardia
    • GI stasis
  • Prognosis is guarded
  • not common since isoflupredone admin became known as the primary predisposing factor

Food Animal Medicine (43 decks)

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