Uroliths and Nutrition Flashcards
Where do oxalates come from?
- A combination of dietary sources
- endogenous synthesis from precursors such as ascorbate and various amino acids
What percentage of kidney stones are composed primarily of calcium oxalate
75%
What are almost all struvite uroliths a consequence of?
- infection of the urinary tract with urease producing microbes (e.g staphylococci)
What are 95% of struvite uroliths linked to in cats?
- Urinary excretion of excessive quantities of dietary minerals
What does acidic urine cause the precipitation of?
- Calcium oxalates
- Uric acid
- Cystine uroliths
What does alkaline urine cause precipitation of?
- Struvite
- Calcium carbonate
- Calcium phosphate
How is calcum oxalate ususally formed?
Over-saturation of urine with calcium and oxalate
Why should you not recommend reducing dietary calcium?
- Reduced complexes with oxalate formed
- Increased intestinal absorption of oxalate
- increased renal excretion of oxalate
What may a low dietary intake of phosphorus be linked to?
Increased urinary calcium excretion
* lower binding of calcium by phosphate ions in the GIT
What can excessive levels of phosphorus in the GIT mean?
- They act as scavengers for calcium
- increase the availability of oxalate uptake in the intestine
What are some of the risk factors for calcium oxalate stones in dogs?
- Dogs under 7
- males
- neutured
What is the link between obesity and urolithiasis?
Glucose load increases urinary oxalate excretion
What is the function of Oxalobacter formigenes?
Gram-Negative anaerobic bacterium
degrades oxalate in the intestinal tract
What is the link between high phosphorus diets and kidney disease?
cats with chronic kidney disease have signficantly higher phosphorus and protein intakes
What is the function of magnesium in the GIT?
- Directly interacts with oxalate to form an insoluble complex
- this lowers the free oxalate concentration in the GIT
- reduction in the absorption of oxalate, less oxalate for excretion via the kidneys
How can you reduce the risk of urolithiasis in cats?
- Increase water intake
- Increase the urinary input
- dilutes the urine
- reduces the risk of CaOx crystallisation in the urinary tract
What is the link between high protein diet and urine?
- Increased protein diet
- acompanied by increased water consumption
- increased urine volume in cats
What is the main risk factor of struvites?
- alkaline urine and increased levels of magnesium, ammonium and phosphate in urine
What is the consequence of a diet low in magnesium?
Prevents struvite urolithiasis
* may also encourage the formation of calcium oxalate
How are struvites produced in the urine?
- Urinary tract infection with urease producing bacteria
- Urine with a high urea concentration (bacteria hydrolyse urea to ammonia)
- Ammonium ions reduce the hydrogen concentration
- Increased urine pH
What increases the likelihood of ruminants getting struvites?
- High grain diets
- low calcium/ phosphorus ratio
- ruminants also graze on silica-rich soil so are predisposed to silica uroliths
How may you prevent struvite calculi?
Increase urinary chloride excretion
* decreases urine pH
What are the common characteristics of diets fed to overweight horses?
- Preserved forages
- low moisture content
- unbalanced mins
- low dry matter intake
What is a single crystal?
a single crystal is where 70% of the urolith is composed of one type of crystal
What is a mixed urolith?
Less than 70% one crystal, there is no identifiable nidus or shell
What is a compound urolith?
Identifiable nidus of one crystal with surrounding layers of another crystal
What is a matrix urolith?
Matrix without an appreciable crystalloid
What are the three ways that crystals form?
- Growth = new crystals are added to the nucleus
- Aggregation = crystals stick together, promoted by cementing substances or viscous bidning materials
- Matrix= made up of lipids and proteins
What does urinary saturation depend on?
- Urinary pH
- Ionic strength
- Solute concentration
- Complexation
What is the main way that uroliths form?
- Urine is full of colloids and crystalloids
- dissolved in solution
- Once saturated, the salt crystallises
- Nucleation/ nidus
What is the primary risk factor for calcium oxalate stones?
hyperoxaluria (urinary oxalate is a key determinant)
What is the main consequence of infection of the urinary tract with urease producing microbes
Almost all struvite uroliths
What are 95% of all cat struvite uroliths linked to?
Urinary excretion of excessive quantities of dietary minerals
Where do calcium oxalate stones occur?
In both the upper and the lower urinary tract of dogs
What is the effect of having a high dietary calcium?
Reduces oxalate absorption
What is the effect of reduced dietary calcium?
- reduces complexion with oxalate in the intestinal lumen
- increases intestinal absorption of oxalate
- Increased renal excretion of both exogenous calcium and oxalate
Why is the aim to reduce oxalate absorption?
- Keeps oxalate in the gut
- Increased faecal excretion
What percentage of uroliths are non-obstructive?
75% of UUT
* removal is not recommended unless they are in pain or any other complications
What is the link between obesity and urolithiasis?
Glucose load increases the urinary oxalate excretion
* Greater mass load = increased urinary oxalate excretion
What is insulin resistance associated with?
defects in the renal ammonium ion production
What is the function of oxalobacter formigenes?
- gram negative anaeroic bacterium
- degrades oxalate in the intestinal tract
- Antibiotic consumption = absence of O.formigenes
What does a diet low in magnesium prevent in cats?
struvite urolithiasis
also encourages the formation of calcium oxalate
What is one of the greatest diet related risk factors for the formation of oxalate calculi?
low-magnesium acidifying diets designed to prevent struvite calculi
What causes struvite calcium oxalate infection?
Urease positive bacteria, i.e Staphylococcus, Streptococcus, Proteus
What are ruminants most predisposed to?
Increased risk of developing struvite uroliths
* high grain diets
* low calcium/ phosphorys ratio
* ruminants graze on silica-rich soil
How may you prevent struvite calculi?
- increased urinary chloride excretion
- decrease in urine pH
How would you minimise urethral calculi?
- add sodium chloride to the total ration
- promote increased sodium and chloride
- increase mineral solubility
How could you reduce urolith formation in equines?
- Decrease the time that urine stays in the bladder
- Addition of 50-75g of salt to the daily ration to increase fluid intake
What factors effect the incidence of urolithiasis in rabbits?
- Decreased water supply
- Decreased activity level
- Low forage intake
