Diet in the aetiology of urolithiasis Flashcards
What is urine full of?
- colloids and crystalloids
When do the stones form?
- when the urine is very saturated
- cant hold in solution
What does the saturation of urine depend on?
- urinary pH
- ionic strength
- solute conc
- complexation
How do the stones form?
- 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
What are the different types of crystal and how are they named?
- 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
What are the 2 main types of stone?
- oxalates
- struvites
What are oxalates?
- anion of a stong dicarboxylic acid
- comes from:
- combo of dietary sources
- endogenous synthesis from precursors such as ascorbate and amino acids
What is hyperoxaluria?
- primary risk factor for oxalate stones
Which stone is more common in dogs and how do they occur?
- struvites (magnesium ammonium phosphate salt)
- UTIs with urease producing microbes
- e.g. staphylococci
What stone formation does an acid/ alkaline pH lead to?
- acid
- precip of calcium oxalates
- uric acid
- crystaline uroliths
- precip of calcium oxalates
- alkaline
- precip of struvite
- calcium carbonate calcium phosphate uroliths
- precip of struvite
How has stone composition changed over the past decades?
- progressive increase of calcium oxalate and calcium phosphate stones
What are the changing trends of stones?
How does obesity increase the prevalence of urolithiasis?
- 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
What is the significance of O.formigenes?
- positively associated with healthy dogs specifically in non-stone breeds
What does the absence of O.formigenes increase the risk of?
- increase risk of absorptive hyperoxaluria
- recurrent episodes of calcium oxalate stones
In what circumstances is O.formigenes levels high in individuals?
- never had antibiotics
- reduces the risk of stone formation
How do antibiotics increase risk of stone formation?
- 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
What climates have been seen to increase incidence of stones?
- higher incidence in warm/ hot climates
- due to low urinary output and scant fluid intake
WHere do CaOx stones normally occur in dogs/cats?
- dogs - upper/lower urinary tract
- cats- tends to be just lower
What are some treatment options for CaOx stones?
- laser lithotripsy
- dietary modification
What % does dierary oxalate contribute to amount excreted in urine?
- 10-20%
What are the dietary factors that affect the risk of CaOx urolithasis?
- dietary Ca (inhibits oxalate absoroption/timing)
- presence of unabsorbed fatty acids
- oxalate degrading microbial flora of gut
- amount of oxalate in diet
What shouldn’t be recommended for animals with CaOx stones?
- 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
- insufficient dietary Ca:
What might low dietary P be related to?
- increased urinary Ca excretion
- lower brinding of Ca by phosphate ions in GIT
- increased Ca absorption
What can excessive P in the GIT lead to?
- 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
What was seen in higher amounts in the diets of cats with chronic kidney disease?
- higher P
- higher protein intakes (>150%) of RD1
- (from bones)
What does magnesium do?
- 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
What are the dietary risks for dogs and cats?
- 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
What are the dietary risks for cats?
- low moisture food
- supplements containing Ca, Vit C, Vit D
- low dietary phosphate
- low dietary sodium
What is the relationship between calcium hypercalciuria and dogs?
- excessive intake of dietary calcium
- impaired renal reabsorption of calcium
- skeletal mobilisation of calcium
How to reduce the risk in cats?
- increase water intake
- increase urinary output
- maintain medium to high protein
Why do you need high fluid intake?
- dilutes the urine
- so reduces the conc of Ca and oxalate in urine
- reduces risk of crystallisation of CaOx in urinary tract
Why increase water levels in cats?
- high moisture and Na
- cats fed kibble - moisture = 7-7.9%
- have a 66% higher risk
- canned food = 77.4-81.2% moisture
By how much does a high (82%) moisture diet increase UO?
57.4%
What do most diets contain which may stimulate drinking?
- mineral (ash)
- protein content
- evoke a higher renal solute load
Why maintain high protein diets in cats?
- high intake increases water consumption/ urine output
- 50% less risk of CaO formation on high protein diets- 105-138g/1000kcal
How would you reduce oxalate in diet?
- reduce leafy green veg, bran, cereals
What are the goals of dietary prevention?
- reduce urine calcium and oxalate conc
- promote high concs and activity of urolith inhibitors
- reduce urine acidity
- maintain dilute urine
What is the association between dry food and struvites in cats?
- association between them
- 75% of the cats with known struvite calculi consumed dry food
What is recommended for cats to prevent struvite calculi/ urethral plugs?
- 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
What are the risk factors for struvites in cats?
- hypermagnesia
- low caloric density - increased food intake
- high urine pH
- low dietary moisture
What is the change in aetiology in cats?
- low Mg diets used to reduce struvites
- now cause apatite nephrolith
Why do you need to balance the anti-stuvite diets?
- 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
What causes struvites in dogs?
- 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
How does diet and infection - dogs?
- 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
At what pH will crystals dissolve?
- pH < 6.3
What increases the risk of struvites in ruminants?
- high grain diets
- low Ca:P ratios
- grazing on silica-rich soil = silica uroliths
How do you control occurence in ruminants?
- 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
- add socium chloride up to 4%
- 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
What are the dietary risk factors for herbivores?
- 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
What are the risk factors for calcium carbonate stones in horses and rabbits?
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
Horses?
- 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%
Dietary risk of overweight horses?
- 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
What % of horses have calculi in multiple locations?
- 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
Rabbits?
- 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
