Page 808 - Small Animal Clinical Nutrition 5th Edition

838 Small Animal Clinical Nutrition

nia and bromsulphalein retention. Other non-Dalmatian miniature schnauzers with ammonium urate uroliths associat-
VetBooks.ir breeds that appear to have a significantly higher incidence of ed with portal vascular anomalies. In these dogs, urine uric acid
concentrations were approximately 50 mg/kg body weight/day
urate urolithiasis based on quantitative urolith analyses are
and urine ammonia concentrations were approximately 1.5
miniature schnauzers, Shih Tzus and Yorkshire terriers
(Osborne et al, 1995). mM/kg body weight/day while the dogs consumed a growth-
Urate uroliths from non-Dalmatian dogs have been recog- type food.When two of these dogs consumed a purine-restrict-
nized most frequently in males. Uroliths have been detected ed food, urine uric acid concentrations were approximately 17
throughout the lifespan of affected dogs; however, they were mg/kg body weight/day and urine ammonia concentrations
most frequently detected in dogs three to six years of age. were approximately 0.6 mM/kg body weight/day.
Regardless of cause, severe hepatic dysfunction may predis- Not all dogs with portal systemic anomalies develop concur-
pose dogs to urate lithogenesis, especially ammonium urate rent ammonium urate urolithiasis. Definition and characteriza-
uroliths. Observations and evidence derived from experimental tion of other factors responsible for promoting or inhibiting
models suggest that prolonged consumption of foods with urate lithogenesis in affected dogs require further investigation.
markedly restricted levels of protein may be associated with for- We have observed urate urocystolith formation in miniature
mation of urate uroliths in dogs (Kruger and Osborne, 1986). schnauzers and Yorkshire terriers with hepatic microvascular
Biochemical and histologic evaluation of these dogs suggests dysplasia. Dogs with this disorder do not have macrovascular
that long-term consumption of foods severely restricted in pro- shunts. Rather, intrahepatic microvascular shunting apparently
tein may induce hepatocellular dysfunction and concomitant occurs. Clinical signs and biochemical abnormalities are similar
hyperuricemia. Hepatic cirrhosis has also been associated with to those seen in dogs with macroscopic vascular shunts. When
urate uroliths in dogs and other species (Rothuizen and van den affected dogs consumed a growth-type food, urinary uric acid
Ingh, 1980). However, foods with severely restricted protein excretion was approximately 30 mg/kg body weight/24 hours,
levels and other causes of hepatic dysfunction have been urinary ammonia excretion was approximately 1.25 mmol/kg
uncommon causes of ammonium urate urolithiasis. None- body weight/24 hours and urinary pH was less than 6.5 pH
theless, their significance relative to ammonium urate lithogen- units. When dogs were fed a purine-restricted food, urinary
esis deserves further study. uric acid excretion was approximately 16 mg/kg body
weight/24 hours, urinary ammonia excretion was approximate-
Dogs with Portal Vascular Anomalies or Hepatic ly 0.5 mmol/kg body weight/24 hours and urinary pH was
Microvascular Dysplasia greater than 7.0 pH units.
Ammonium urate uroliths have frequently been observed in Not all dogs with portal systemic anomalies or hepatic
dogs with portal vascular anomalies. These uroliths occur in microvascular dysplasia develop concurrent ammonium urate
males and females and usually have been detected before dogs urolithiasis. Definition and characterization of other factors
reach three years of age (Rothuizen and van den Ingh, 1980; responsible for promoting or inhibiting urate lithogenesis in
Marretta et al, 1981; Hardy and Klausner, 1983; Kruger and affected dogs require further investigation.
Osborne, 1986).
Direct communication between the portal and systemic vas- Dietary Risk Factors
culature shunts blood around the liver. Severe hepatic atrophy Concentrations of lithogenic substances in urine depend on urine
and diminished hepatic function may occur as a result. Hepatic volume. Because commercial dry foods are associated with pro-
dysfunction in turn is associated with reduced hepatic conver- duction of less urine compared with moist foods,consumption of
sion of uric acid to allantoin and reduced conversion of ammo- dry foods is likely a risk factor for urate urolith formation.
nia to urea. The predisposition of dogs with portal vascular Dalmatian dogs consuming foods containing more than 20%
anomalies to urate urolithiasis is probably associated with con- dry matter (DM) protein, and protein sources high in purines
comitant hyperuricemia, hyperammonemia, hyperuricuria and and purine precursors (Table 39-3) are at increased risk for
hyperammonuria (Kruger and Osborne, 1986; Hardy and urate lithogenesis. Because urate uroliths associated with portal
Klausner, 1983). Serum uric acid concentrations in 15 dogs vascular anomalies are often diagnosed in dogs less than one
with portal vascular anomalies evaluated at the University of year of age, it is probable that they were consuming foods with
Minnesota Veterinary Teaching Hospital were increased (val- increased protein content.
ues ranged from 1.2 to 4.0 mg/dl) (Hardy and Klausner, 1983). Urine acidity is a risk factor for urate lithogenesis because the
Concurrent hyperuricuria, hyperammonuria, hyperuricemia solubility of most purines, especially ammonium urate, is pH-
and hyperammonemia were observed in an 18-month-old dependent. Therefore, consumption of foods that promote
Bernese mountain dog with recurrent ammonium urate aciduria (e.g., high-protein foods or those with other acidifying
uroliths associated with a portal vascular anomaly (Kruger and ingredients) may be a risk factor.
Osborne, 1986). This dog had a urine uric acid concentration
of 42 mg/kg body weight/day and a urine ammonia concentra-
tion of 3.2 mM/kg body weight/day while the dog was fed a BIOLOGIC BEHAVIOR
protein-restricted food. Hyperuricuria, hyperammonuria,
hyperuricemia and hyperammonemia were observed in three Purine uroliths have the potential to undergo spontaneous dis-