Hypomagnesemia Flashcards
(28 cards)
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
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
- Different mechanisms of absorption help maintian net uptake and continuous inflow with varied intra-ruminal Mg concentrations
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
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
5
Q
What hormones influence Mg?
A
- Secondary influence:
- PTH
- ALdosterone
- Vit D
- etc
6
Q
What stimulates Mg flux from ECF pool to tissue?
A
- Transport exertion
- Insulin, epinephrine, norepinephrine - likely cause an intracellular influx
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
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
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
10
Q
What are the differentials for Hypomagnesemia?
A
- Rabies
- Nervous ketosis
- dairy cows
- Bovine spongiform encephalopathy
- Downer cow syndrome
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
12
Q
what samples can be taken post-mortem to test for magnesium levels?
A
- CSF
- Vitreous humor - good for 48hrs on ice
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
- Recumbent/convulsing
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
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
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
- Extracellular 5-8g
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
How is Potassium homeostasis maintained in cows?
* 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
What are causes of hypokalemia?
* Anorexia
* Muscle catabolism - protein deficiency
* Excessive aldosterone secretion
* Isoflupredone
* Diuretics
* Acetazolamide, Thiazide \>\>furosemide
* Insulin
* exogenous \>\> endogenous
* Stress
* Hypochloremia
27
What does potassium have to do with resting membrane potential?
* 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
What is Hypokalemia syndrome?
* Profound weakness/recumbency
* S-curved neck
* Tachycardia
* GI stasis
* Prognosis is guarded
* not common since isoflupredone admin became known as the primary predisposing factor
