ansc314 - mineral P

phosphorus (P)

performs 14 vital functions

• free P does NOT exist

• P always chelated or bound as phosphate

P sources animal

cereal grains

• ↑ P, poorly available (20-60%) as it is bound as phytic acid

P sources human

P sources ruminants

microbial phytases breakdown phytic acid in cereal grains → release P that’s absorbed in s. intestine

• ruminants have ↓ P requirement → don’t need phytase in diet

phytic acid

plant storage form of P

• chelation

  • Mg, Zn, Cu, Ca, Mn , Fe & K (cations)

  • Occurs in plant & precipitates minerals in digestion cations)

  • ↑ phytate prevents P release by animal enzymes

P functions

• bone & teeth formation

• ↑ E bonds (ATP → ADP, creatine-P → creatine)

• lipid transport (phospholipids)

• nucleic acid synthesis (DNA, RNA)

• milk secretion (casein micelle formation)

• osmotic & acid-base balance (phosphate buffer system)

• carbohydrate, fat & amino acid metabolism (phosphorylation, events, enzyme control)

• enzyme system requirements

P blood & body distribution

P represents 1.1% of fat-free mass of body

• 80-85% of body P → bones & teeth

  • ↑ skeletal P w/ ↑ maturity → ↑ ossification

• soft tissue (14%)

• blood (1%)

  • plasma lvls (60-90 mg phosphate/L)

P absorption sites

duodenum & upper jejunum

• rapid absorption unless bound (phytate)

• bound to phospholipid in intestinal epithelium (not free)

P absorption mechanisms

• saturable (70% dietary P absorbed)

• carrier-mediated ACTIVE transport against concentration gradient

• some passive uptake

• excess P intake depresses Ca absorption due to formation insoluble Ca phosphates in s. intestine

P absorption factors

• excessive lvls of

  • Ca, Mg, Al → ties PO₄ (precipitates) & ↓ absorption

    • diet acidity helps dissolve precipitates (↓ pH)

• phosphate form

  • Dicalcium Phosphate – 85% available (more soluble)

  • Ca Phosphate – 45% available (less soluble)

  • Phytate-P – low and variable in monogastric species

• phytic acid & animal/bacterial phytase

  • presence or absence

phytate complex (P availability)

• monogastric

  • fed grain-based diets:

    • add more mineral P supplements

    • add phytase to the diet

• ruminants

  • rumen microbial phytases release P from phytate complex in rumen

    • don’t need to add phytase

• adding extra mineral P to diets problems

  • ends up in feces → water

  • finite supply of mineral phosphate mines

phytase sources

• ruminal & intestinal bacteria

• added to diet (from bacteria)

• plant – low

• animal phytase → very low levels of enzyme in intestine

  • except Enviro-pig

P excreted by broilers

• excess P ends up in animal manures

  • ↑ eutrophication of fresh water

  • most MD broiler producers feed phytase to ↓ impact on water

  • required by law in NC for swine

plant phytate-P sources

10-60% P availble from grains

• corn, oats

• wheat, barley, rice

• soybeans

  • processing wheat flour makes phytate-P available (grinding & baking)

P requirements

0.3 to 1% of diet

• Ca:P ratio very important

• Ca:P < 1:1 or >2.5:1 metabolic problems

P deficiency

• rickets & osteomalacia (same as Ca)

• abnormal growth & bone structure

• appetite loss (anorexia)

• Pica - abnormal eating & chewing behavior

  • chew wood, bones, & other material, & eat soil

• ↓ blood P - hypophosphatemia

excess P

common deficiency in humans

• low Ca:P ratio

• feeding meat meal or cereals (↓ Ca:P ratio)

• symptoms

  • hyperparathyroidism

  • ↑ PTH →

    • ↑ PO₄ = excretion

    • ↑ Ca resorption from bone

    • ↑ Ca intestinal absorption to offset ↑ plasma Ca

  • bone calcification failure

• ↑ P & Mg → minerals deposits in bladder ""urolithiasis”

P homeostasis (↑ P)

response to ↑ P diet

• ↑ diet P → ↓ active D₃, ↑ PTH, ↑ bone mobilization

P homeostasis (↓ P)

response to ↓ P diet

• ↓ P → active ↑ D₃, ↓ PTH → restore serum Ca

  • can be caused by kidney dysfunction, alcoholism, diabetes, medications