Objective—To evaluate the effects of a high-protein
diet versus dietary supplementation with ammonium
chloride (NH4Cl) on struvite crystal formation in the
urine of clinically normal cats by measuring the urine
concentration of hydrochloric acid (HCl)-insoluble sediment,
urine pH, struvite activity product (SAP), number
of struvite crystals in urine, and urine volume.
Animals—23 healthy adult cats.
Procedure—Urine was fractionated by centrifugation
with subsequent extraction of the sediment with 1 N
HCl (study 1). Diets containing either 29% crude protein
or 55% crude protein were fed to cats in a
crossover trial of 3 weeks/period (study 2). Diets supplemented
with either sodium chloride (NaCl) or
NH4Cl were fed, by use of a 3 X 3 Latin-square design
with 3 wk/period (study 3). In studies 2 and 3, urine
samples were collected for the last 7 days of each
Results—The HCl-insoluble sediment contained
Tamm-Horsfall glycoprotein (THP; study 1). The highprotein
diet (study 2) and dietary supplementation
with NH4Cl (study 3) resulted in a decrease in urine
pH, SAP, and the number of struvite crystals in urine.
However, the high-protein diet decreased urine concentrations
of HCl-insoluble sediment containing THP
(study 2), in contrast to the NH4Cl supplementation
that increased urine volume without a significant
effect on the urine concentration of the HCl-insoluble
sediment (study 3).
Conclusions and Clinical Relevance—Our results
indicate that compared with dietary supplementation
with NH4Cl, the high-protein diet is preferable as a
urine acidifier for the prevention of struvite crystal formation
in clinically normal cats. (Am J Vet Res
Procedure—Diets containing no carbohydrate source
(control diet), control plus starch, or control plus fiber
were given in a 3 × 3 Latin-square design. The diets
were available ad libitum in study 1 (n = 12) and given
under restrictions in study 2 (9) to equalize daily
intakes of crude protein among the 3 groups.
Formation of struvite crystals and balance of calcium,
phosphorus, and magnesium were measured.
Results—Urine volume was lower in the starch group
and fiber group in study 1, whereas no differences
were detected among the groups in study 2. Urinary
pH and struvite activity product were higher in the
starch group in both studies, and the fiber group also
had higher struvite activity product in study 2. In both
studies, urinary concentrations of HCl-insoluble sediment
were higher in the starch group and fiber group.
In the fiber group, a net loss of body calcium, phosphorus,
and magnesium was detected in study 2.
Conclusions and Clinical Relevance—Starch and
fiber in diets potentially stimulate formation of struvite
crystals. Hence, reducing dietary carbohydrate is
desirable to prevent struvite urolith formation. In addition,
a net loss of body calcium, phosphorus, and
magnesium during feeding of the fiber diet suggests
that dietary inclusion of insoluble fiber could increase
macromineral requirements of cats. (Am J Vet Res