Diet in the aetiology of urolithiasis

Question 1

What is urine full of?

Answer 1

• colloids and crystalloids

Question 2

When do the stones form?

Answer 2

• when the urine is very saturated
• cant hold in solution

Question 3

What does the saturation of urine depend on?

Answer 3

• urinary pH
• ionic strength
• solute conc
• complexation

Question 4

How do the stones form?

Answer 4

• 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

Question 5

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

Answer 5

• 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

Question 6

What are the 2 main types of stone?

Answer 6

• oxalates
• struvites

Question 7

What are oxalates?

Answer 7

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

Question 8

What is hyperoxaluria?

Answer 8

• primary risk factor for oxalate stones

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

How has stone composition changed over the past decades?

Answer 11

• progressive increase of calcium oxalate and calcium phosphate stones

Question 12

What are the changing trends of stones?

Answer 12

Question 13

How does obesity increase the prevalence of urolithiasis?

Answer 13

• 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

Question 14

What is the significance of O.formigenes?

Answer 14

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

Question 15

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

Answer 15

• increase risk of absorptive hyperoxaluria
• recurrent episodes of calcium oxalate stones

Question 16

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

Answer 16

• never had antibiotics
• reduces the risk of stone formation

Question 17

How do antibiotics increase risk of stone formation?

Answer 17

• 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

Question 18

What climates have been seen to increase incidence of stones?

Answer 18

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

Question 19

WHere do CaOx stones normally occur in dogs/cats?

Answer 19

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

Question 20

What are some treatment options for CaOx stones?

Answer 20

• laser lithotripsy
• dietary modification

Question 21

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

Answer 21

• 10-20%

Question 22

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

Answer 22

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

Question 23

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

Answer 23

• 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

Question 24

What might low dietary P be related to?

Answer 24

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

Question 25

What can excessive P in the GIT lead to?

Answer 25

* 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

Question 26

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

Answer 26

* higher P * higher protein intakes (\>150%) of RD1 * (from bones)

Question 27

What does magnesium do?

Answer 27

* 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

Question 28

What are the dietary risks for dogs and cats?

Answer 28

* 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

Question 29

What are the dietary risks for cats?

Answer 29

* low moisture food * supplements containing Ca, Vit C, Vit D * low dietary phosphate * low dietary sodium

Question 30

What is the relationship between calcium hypercalciuria and dogs?

Answer 30

* excessive intake of dietary calcium * impaired renal reabsorption of calcium * skeletal mobilisation of calcium

Question 31

How to reduce the risk in cats?

Answer 31

* increase water intake * increase urinary output * maintain medium to high protein

Question 32

Why do you need high fluid intake?

Answer 32

* dilutes the urine * so reduces the conc of Ca and oxalate in urine * reduces risk of crystallisation of CaOx in urinary tract

Question 33

Why increase water levels in cats?

Answer 33

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

Question 34

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

Answer 34

57.4%

Question 35

What do most diets contain which may stimulate drinking?

Answer 35

* mineral (ash) * protein content * evoke a higher renal solute load

Question 36

Why maintain high protein diets in cats?

Answer 36

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

Question 37

How would you reduce oxalate in diet?

Answer 37

* reduce leafy green veg, bran, cereals

Question 38

What are the goals of dietary prevention?

Answer 38

* reduce urine calcium and oxalate conc * promote high concs and activity of urolith inhibitors * reduce urine acidity * maintain dilute urine

Question 39

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

Answer 39

* association between them * 75% of the cats with known struvite calculi consumed dry food

Question 40

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

Answer 40

* 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

Question 41

What are the risk factors for struvites in cats?

Answer 41

* hypermagnesia * low caloric density - increased food intake * high urine pH * low dietary moisture

Question 42

What is the change in aetiology in cats?

Answer 42

* low Mg diets used to reduce struvites * now cause apatite nephrolith

Question 43

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

Answer 43

* 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

Question 44

What causes struvites in dogs?

Answer 44

* 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

Question 45

How does diet and infection - dogs?

Answer 45

* 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

Question 46

At what pH will crystals dissolve?

Answer 46

* pH \< 6.3

Question 47

What increases the risk of struvites in ruminants?

Answer 47

* high grain diets * low Ca:P ratios * grazing on silica-rich soil = silica uroliths

Question 48

How do you control occurence in ruminants?

Answer 48

* 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

Question 49

What are the dietary risk factors for herbivores?

Answer 49

* 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

Question 50

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

Answer 50

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

Question 51

Horses?

Answer 51

* 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%

Question 52

Dietary risk of overweight horses?

Answer 52

* 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

Question 53

What % of horses have calculi in multiple locations?

Answer 53

* 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

Question 54

Rabbits?

Answer 54

* 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