HypoMg, HypoP Flashcards
how is phosphate usually supplied and excreted from the body?
Normally supplied by diet, with excess
excreted via saliva, urine, and feces
how can hypophosphatemia arise?
Decreased intake of P (reduced DMI)
> Primary hypophosphatemia in dairy cattle is unusual
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Hypophosphatemia follows hypocalcemia
During HypoCa++…
> PTH causes renal excretion of P to retain Ca.
> Salivary P (in the form of phosphate buffers) pool in the rumen (hypomotility). Phosphorus is not absorbed in the rumen wall; it
must pass on to the small intestine (absorbed back into circulation)
when should we consider hypophosphatemia? what to keep in mind?
- consider in downer cows refractory to Ca admin
> alert
> good appetite
> recumbent for no apparent reason - but most likely NOT the cause of recumbency
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Small % of cows with hypophosphatemia secondary to hypocalcemia remain hypophosphatemic after Ca administration
why is hypophosphatemia controversial?
No evidence it causes downers or that treatment improves condition.
hypophosphatemia treatment
Most resolve with IV Ca++ administration
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- Phosphate anion (PO )
> Sodium monophosphate intravenously
> Fleet enema (dilute in 1L sterile water or saline)
> Incompatible with calcium solutions
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- oral phosphate
> preferred method in mild to moderate cases
> eg. 200 to 300 grams of monosodium phosphate mixed with 1.5 L warm water (via oro‐gastric tube)
problem with hypophosphites for treating hypophosphatemia
not biologically available to the cow
issue with mixing phosphate anion with Ca
IV sodium phosphate + calcium = insoluble Ca phosphate crystals (in the bottle or in the blood stream if within 2 hours after giving IV Ca)
hypophosphatemia signalment / what animals more often affected
More often, a problem of beef cows and ewes: * Late pregnancy, often carrying twins
* Associated with poor nutrition
*May see herd issues:
> Unthrifty
> poor reproductive problems
possible sign of hypophosphatemia after parturition?
Post‐parturient hemoglobinuria
(reported in New Zealand)
Hypomagnesemic tetany other names
“Hypomagnesemia”
“Lactation tetany”
“Grass tetany”
“Grass staggers”
Hypomagnesemia and Hypocalcemia Relationship
chronic hypomagnesemia > increases susceptilibity to hypocalcemia
-Mg required as cofactor for PTH receptor so it can signal to upregulate 1,25-(OH)2 vitamin D, etc.
Hypomagnesemic tetany etiology? beef vs dairy cattle?
- low serum Mg
- grazing of heavily-fertilized pastures during lactation
- beff > dairy cattle
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hypomagnesemia inflow vs outflow
> absence of specific hormonal mechanisms for compensation - Oral intake > most excreted in feces, some absorbed into extracellular space > excreted in urine, milk
> Mg secretion into the milk continues independently of [Mg] in the extracellular fluid
Hypomagnesemic tetany risk factors from feed
- Pasture feeding: lush, rapid growth
Risk Factors - Heavily fertilized with nitrogen +/‐ potassium
(compete with magnesium for uptake by plant) - Clinical episodes occur shortly following cold, wet weather or any other major stress (sudden decrease in feed intake)
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increased risk if grass contains: - high [K]
- low [Na]
- high [crude protein]
hypomagnesemic tetany risk factors from cattle /animals and weather
- Beef Cattle on Pasture
- Older cattle (> 6 years)
- first 6-8 weeks of lactation
- high producing cows
- Seasonal: spring, fall
- also mature ewes
- Can also occur in male animals, young animals (2‐4 months old on whole milk)
Hypomagnesemic tetany clinical signs
- Decreased appetite, drop in milk yield
- Mild agitation, nervousness, hyperesthesia
- Hypersalivation, bruxism
- Fine muscle tremors
- High‐stepping, stiff gait
- Incoordination, progressive ataxia
- Down cow - resembles milk fever, but stronger, more agitated
- tachycardia
- tetany and convulsions
- “Sudden death”, “Found dead”
