title: Red blood cell phosphate concentration and osmotic resistance during dietary phosphate depletion in dairy cows.
abstract: BACKGROUND
  Hypophosphatemia in early lactating dairy cows has been implicated as primary cause for postparturient hemoglobinuria in cattle. Decreased availability of phosphorus has been proposed to reduce adenosine triphosphate synthesis of erythrocytes and thereby reduce osmotic resistance of these cells.
  
  
  OBJECTIVE
  To study the effect of phosphorus depletion on the phosphate concentration ([Pi]) in plasma and erythrocytes and the osmotic resistance of erythrocytes and to determine the association between plasma [Pi] and erythrocyte [Pi].
  
  
  METHODS
  Ten healthy midlactating dairy cows in their 3rd to 5th lactation.
  
  
  METHODS
  Prospective study. Dietary phosphorus depletion for 5 weeks followed by phosphorus supplementation. Plasma and erythrocyte [Pi] and erythrocyte osmotic resistance were measured. Four cows underwent continuous dextrose infusion at the end of phosphate depletion to exacerbate hypophosphatemia.
  
  
  RESULTS
  Dietary P depletion resulted in a marked decline of the plasma [Pi] from 4.1 ± 1.0 mg/dL to a nadir of 1.7 ± 0,5 mg/dL, but did not alter erythrocyte [Pi] or osmotic resistance. Similarly, dextrose infusion induced a decline of the plasma [Pi] from 2.4 ± 0.5 mg/dL to 1.5 ± 0.5 mg/dL, but had no effect on erythrocyte [Pi] or osmotic resistance.
  
  
  CONCLUSIONS
  In cattle, marked hypophosphatemia induced by dietary P depletion was neither associated with a decline in erythrocyte [Pi] nor with decreased osmotic resistance of erythrocytes. Phosphorus depletion alone is therefore unlikely to cause intravascular hemolysis and the plasma [Pi] is an unreliable index for the intracellular [Pi] of erythrocytes.
authors.affiliation: Department of Farm Animal Health, Utrecht University, Utrecht, The Netherlands.
authors.forename: W
authors.initials: W
authors.lastname: Grünberg
authors.forename: J A
authors.initials: JA
authors.lastname: Mol
authors.forename: E
authors.initials: E
authors.lastname: Teske
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D004912:Erythrocytes / Q000737:chemistry / Q000502:physiology*; D005260:Female; D009997:Osmotic Pressure; D010710:Phosphates / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D016226:Phosphorus, Dietary / Q000008:administration & dosage* / Q000494:pharmacology
chemical_list: D010710:Phosphates; D016226:Phosphorus, Dietary
keywords: Hemolysis; Hypophosphatemia; Osmotic resistance; Postparturient hemoglobinuria