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FD6 > Diet in the aetiology of urolithiasis > Flashcards

Diet in the aetiology of urolithiasis Flashcards

1
Q

What is urine full of?

A
  • colloids and crystalloids
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2
Q

When do the stones form?

A
  • when the urine is very saturated
  • cant hold in solution
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3
Q

What does the saturation of urine depend on?

A
  • urinary pH
  • ionic strength
  • solute conc
  • complexation
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4
Q

How do the stones form?

A
  • growth
    • new crystals added to nucleus
  • aggregation
    • crystals stick together promoted by cemented substances or viscous binding molecules
  • matrix
    • lipids (10% of stone matrix)- membrane phospholipids formation of calcium oxalate and phosphate
    • proteins- various macromolcules
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5
Q

What are the different types of crystal and how are they named?

A
  • single crystal (70% of urolith is 1 type of crystal) - named after that crystal
  • mixed urolith (<70% 1 crystal; no identifiable nidus/shell
  • compound urolith (identifiable nidus of 1 crystal with surrounding layers of another)
  • matrix urolith
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6
Q

What are the 2 main types of stone?

A
  • oxalates
  • struvites
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7
Q

What are oxalates?

A
  • anion of a stong dicarboxylic acid
  • comes from:
    • combo of dietary sources
    • endogenous synthesis from precursors such as ascorbate and amino acids
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8
Q

What is hyperoxaluria?

A
  • primary risk factor for oxalate stones
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9
Q

Which stone is more common in dogs and how do they occur?

A
  • struvites (magnesium ammonium phosphate salt)
  • UTIs with urease producing microbes
  • e.g. staphylococci
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10
Q

What stone formation does an acid/ alkaline pH lead to?

A
  • acid
    • precip of calcium oxalates
      • uric acid
      • crystaline uroliths
  • alkaline
    • precip of struvite
      • calcium carbonate calcium phosphate uroliths
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11
Q

How has stone composition changed over the past decades?

A
  • progressive increase of calcium oxalate and calcium phosphate stones
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12
Q

What are the changing trends of stones?

A
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13
Q

How does obesity increase the prevalence of urolithiasis?

A
  • glucose load increases urinary oxalate excretion
  • greater BMI = associated with increased urinary oxalate excretion
  • hyperinsulinemia increases the urinary excretion of calcium
  • insulin resistance = associated with defected in renal ammonium ion production
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14
Q

What is the significance of O.formigenes?

A
  • positively associated with healthy dogs specifically in non-stone breeds
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15
Q

What does the absence of O.formigenes increase the risk of?

A
  • increase risk of absorptive hyperoxaluria
  • recurrent episodes of calcium oxalate stones
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16
Q

In what circumstances is O.formigenes levels high in individuals?

A
  • never had antibiotics
  • reduces the risk of stone formation
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17
Q

How do antibiotics increase risk of stone formation?

A
  • o.formigenes = gram -ve anaerobic bacterium that degrades oxalate in intestines
  • antibiotic consumption = absence of O.formigenes
  • absence of intestinal O.formigenes could represent pathogenic factor
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18
Q

What climates have been seen to increase incidence of stones?

A
  • higher incidence in warm/ hot climates
  • due to low urinary output and scant fluid intake
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19
Q

WHere do CaOx stones normally occur in dogs/cats?

A
  • dogs - upper/lower urinary tract
  • cats- tends to be just lower
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20
Q

What are some treatment options for CaOx stones?

A
  • laser lithotripsy
  • dietary modification
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21
Q

What % does dierary oxalate contribute to amount excreted in urine?

A
  • 10-20%
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22
Q

What are the dietary factors that affect the risk of CaOx urolithasis?

A
  • dietary Ca (inhibits oxalate absoroption/timing)
  • presence of unabsorbed fatty acids
  • oxalate degrading microbial flora of gut
  • amount of oxalate in diet
23
Q

What shouldn’t be recommended for animals with CaOx stones?

A
  • shouldnt recommend reduced/excess Ca
    • insufficient dietary Ca:
      • reduces complexion with oxalate in the intestinal lumen
      • increases intestinal absorption of oxalate
      • increases renal excretion of both exogenous Ca and oxalate
24
Q

What might low dietary P be related to?

A
  • increased urinary Ca excretion
  • lower brinding of Ca by phosphate ions in GIT
  • increased Ca absorption
25
Q

What can excessive P in the GIT lead to?

A
  • phosphate can act as a scavenger for Ca, thereby indirectly increasing the availability of oxalate for uptake by the intestine
  • could compete with oxalate
  • prevent intestinal Ca complexation with oxalate
  • could increase the availability of free oxalate
  • increased intestinal absorption and renal excretion of oxalate
26
Q

What was seen in higher amounts in the diets of cats with chronic kidney disease?

A
  • higher P
  • higher protein intakes (>150%) of RD1
  • (from bones)
27
Q

What does magnesium do?

A
  • directly interacts with oxalate to form an insoluble complex
  • lowers the free oxalare conc in the GIT
  • reduce the absorption of oxalate
  • less oxalate for excretion via kidneys
  • check Mg levels of diet
28
Q

What are the dietary risks for dogs and cats?

A
  • not drinking enough
  • excess calorie intake = obesity
  • veg high in oxalate, sugar beer, soyabean fibre
  • Mg restricted diets
  • use of struvite preventative diets - acidifying, low Mg
29
Q

What are the dietary risks for cats?

A
  • low moisture food
  • supplements containing Ca, Vit C, Vit D
  • low dietary phosphate
  • low dietary sodium
30
Q

What is the relationship between calcium hypercalciuria and dogs?

A
  • excessive intake of dietary calcium
  • impaired renal reabsorption of calcium
  • skeletal mobilisation of calcium
31
Q

How to reduce the risk in cats?

A
  • increase water intake
  • increase urinary output
  • maintain medium to high protein
32
Q

Why do you need high fluid intake?

A
  • dilutes the urine
  • so reduces the conc of Ca and oxalate in urine
  • reduces risk of crystallisation of CaOx in urinary tract
33
Q

Why increase water levels in cats?

A
  • high moisture and Na
  • cats fed kibble - moisture = 7-7.9%
  • have a 66% higher risk
  • canned food = 77.4-81.2% moisture
34
Q

By how much does a high (82%) moisture diet increase UO?

A

57.4%

35
Q

What do most diets contain which may stimulate drinking?

A
  • mineral (ash)
  • protein content
  • evoke a higher renal solute load
36
Q

Why maintain high protein diets in cats?

A
  • high intake increases water consumption/ urine output
  • 50% less risk of CaO formation on high protein diets- 105-138g/1000kcal
37
Q

How would you reduce oxalate in diet?

A
  • reduce leafy green veg, bran, cereals
38
Q

What are the goals of dietary prevention?

A
  • reduce urine calcium and oxalate conc
  • promote high concs and activity of urolith inhibitors
  • reduce urine acidity
  • maintain dilute urine
39
Q

What is the association between dry food and struvites in cats?

A
  • association between them
  • 75% of the cats with known struvite calculi consumed dry food
40
Q

What is recommended for cats to prevent struvite calculi/ urethral plugs?

A
  • restricted magnesium diet
  • Ca:P = 1:1
  • feeding 1-2x a day - avoid continous postprandial urinary alkalinisatio.
  • provide urinary acidifier - below pH 6.6
  • encourage water intake and activity
41
Q

What are the risk factors for struvites in cats?

A
  • hypermagnesia
  • low caloric density - increased food intake
  • high urine pH
  • low dietary moisture
42
Q

What is the change in aetiology in cats?

A
  • low Mg diets used to reduce struvites
  • now cause apatite nephrolith
43
Q

Why do you need to balance the anti-stuvite diets?

A
  • high protein diets acidify urine - reduce struvites
  • but greatest risk factor for formation of oxalate calculi = low Mg acidifying diets
  • 1:3 cats with oxalate calculi was fed an ant-struvite diet
44
Q

What causes struvites in dogs?

A
  • UTIs with urease producing bacteria
  • urine with high urea conc
    • bacteria hydrolyse urea to ammonia (urease)
    • ammonium ions reduce H conc
    • increase urine pH = alkaline
45
Q

How does diet and infection - dogs?

A
  • urea comes from dietary protein
  • high protein = high P
  • = struvite + calcium phosphate (calcium apatite)
  • = struvite + calcium carbonate phosphate (carbonate apatite)
  • depends on urine conc of minerals, urine pH
46
Q

At what pH will crystals dissolve?

A
  • pH < 6.3
47
Q

What increases the risk of struvites in ruminants?

A
  • high grain diets
  • low Ca:P ratios
  • grazing on silica-rich soil = silica uroliths
48
Q

How do you control occurence in ruminants?

A
  • struvites:
    • increase urinary chloride excretion
    • decrease urine pH
    • provide Ca:P - 2:1
  • urethral calculi
    • add socium chloride up to 4%
      • increased sodium and chloride conc in urine
      • increases water intake and urine dilution
  • ammonium chloride - urinary acidifying agent
    • 7-10g/ head/ day for a 30kg lamb or kid
    • 50-80g/ head/ day for a 240g steer
    • dissolve the stones
49
Q

What are the dietary risk factors for herbivores?

A
  • fed high grain diets with 1:1 Ca;P - rabbits (spinach, parsely, strawbeeries and vit C)
  • high Mg
  • high Ca = calcium carbonate uroliths - low water intake
  • sugar beet tops - factor in calcium oxalate formation
  • mineral comp of water, dietary mineral imbalances - high intakes of alfalfa
50
Q

What are the risk factors for calcium carbonate stones in horses and rabbits?

A

rabbits

  • Ca absorbed directly proportional - not reliant on vit D
  • high dietary oxalate
  • lack of exercise
  • obesity

horses

  • males > mares
  • geldings>stallions
  • excrete lots of Ca carbonate
  • alkaline urine
  • mucus decreases formation and aggregatio
  • low Mg

high protein and calcium. - alfalfa

low water

51
Q

Horses?

A
  • excrete a large amount of calcium carbonate crystals in urine
  • alkaline pH - favours crystallisation
  • not common
  • estimated- 0.11-7.8% of UT diseases
  • bladder = 60%
  • urethra = 24%
  • renal = 12%
  • ureteral = 4%
52
Q

Dietary risk of overweight horses?

A
  • preserved forages
  • low Ca
  • low moisture content
  • unbalanced minerals
  • male
  • low DMI
  • associated woth alfalfa - high in Ca
  • may be prevented by decreasing the time the urine remains in bladder
  • add 50-75g salt - increase fluid intake - promote diuresis
53
Q

What % of horses have calculi in multiple locations?

A
  • 10%
  • nephroliths - may be more important in pathogenesis of urolithiasis
  • amount of Ca excreted strongly correlated with dietary intake
  • remove calcium rich feeds e.g. alfalfa, replace with increases grain and grass hay
  • reduce the cation-anion balance and decrease urinary pH
54
Q

Rabbits?

A
  • absorb more Ca than needed
  • free-ranging rabbits adapted to high Ca
  • heavier kidneys
  • more urinary sediment in sonography
  • increased urinary Ca content - but no signs of urolithiasis
  • grass-hay diets recommended if issue

FD6 (15 decks)

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