Page 918 - Small Animal Clinical Nutrition 5th Edition

950 Small Animal Clinical Nutrition

Sodium research indicates that urinary calcium excretion increases
VetBooks.ir Increasing the salt (i.e., sodium chloride) content of food is an when healthy cats are fed a high-salt food (Biourge et al,
2001). Also, as mentioned above, cats prone to the develop-
effective method for increasing water intake and causing subse-
ment of calcium oxalate urolithiasis benefit from avoiding
quent urine dilution in healthy cats (Hawthorne and Markwell,
2004; Luckshander et al, 2004). However, most factors that increased sodium intake (Lulich et al, 2004). Thus, to avoid
promote natriuresis tend to increase urinary calcium excretion, excess calcium excretion and the possibility of formation of
which could increase risk for calcium oxalate uroliths. Calcium calcium oxalate crystals while feeding these types of foods, a
and sodium are reabsorbed at common sites in the renal sodium range of 0.3 to 0.6% DM is recommended in foods
tubules. Hypercalciuric people who form calcium-containing intended for struvite dissolution.
uroliths appear to have a proportionally greater increase in uri- Cats fed foods containing 1.43 to 3.7 mg of sodium/kcal
nary calcium excretion than non-urolith formers. Increasing (0.57 to 1.48% DM, for a food with 4 kcal ME/g DM) were
dietary sodium intake from 140 to 310 mmol/day increased 4.1 times as likely to develop struvite uroliths as cats consum-
urinary calcium excretion by 34% and decreased urinary citrate ing foods with less sodium (0.48 to 0.77 mg/kcal; 0.19 to 0.31%
by 10% (Kok et al, 1990). However, urinary calcium and sodi- DM, for a food with 4 kcal ME/g DM) (Lekcharoensuk et al,
um excretion was not correlated in healthy people with low 2001a). In this epidemiologic study there was a significant cor-
dietary calcium intake (Dawson-Hughes et al, 1996). relation between high sodium and high phosphorus content in
Effects of increased sodium intake on urinary excretion of foods. It is possible that increased risk for struvite uroliths in
calcium or urinary calcium oxalate saturation in cats with calci- cats eating high-sodium foods is related to the type of sodium
um oxalate uroliths have not been reported. Increased urinary salt (e.g., monosodium phosphate, sodium tripolyphosphate)
excretion of calcium was identified in cats with mild, naturally used in foods. However, additional study is needed to confirm
occurring chronic kidney disease consuming a food with 1.2% this. There are no reported studies evaluating effects of
DM sodium compared with consumption of a food containing increased sodium intake in cats with naturally occurring stru-
0.4% DM sodium (Kirk et al, 2006). Additional study of effects vite uroliths.The recommended range of dietary sodium intake
of increased sodium intake on urinary calcium excretion in cats for prevention of struvite disease in cats is 0.3 to 0.6% DM.
with kidney disease is indicated because nephroliths and In order to cause production of dilute urine, food must con-
ureteroliths, which are most often calcium oxalate, are being tain more than 1% DM sodium. Many foods formulated for
diagnosed more often in cats with chronic kidney disease (Ross cats with lower urinary tract diseases contain between 0.3 and
et al, 2005, 2007). 0.6% DM sodium, whereas, some contain 1 to 1.4% DM sodi-
In healthy cats fed a high-salt food, urine calcium concentra- um. The minimum recommended allowance of sodium for
tion and calcium oxalate saturation were not increased, although adult cats is 0.068% DM (NRC, 2006). According to the most
there was a significant increase in 24-hour urine calcium excre- recent information published by the National Research Council
tion (Biourge et al, 2001).This was likely due to dilution of cal- (NRC), it is difficult to suggest a safe upper limit of sodium for
cium and other substances in urine associated with increased healthy adult cats (NRC, 2006). The NRC has concluded that
urine volume. In another study of healthy cats, increased dietary as long as unlimited amounts of water are available, cats prob-
sodium was associated with increased water intake and urine ably can tolerate reasonably high concentrations of dietary
volume and significantly decreased values for calcium oxalate sodium; the safe upper limit for adult cats has been defined as
urine saturation (Hawthorne and Markwell, 2004). greater than 1.5% DM. However, the safe upper limit of sodi-
In an epidemiologic study, feeding foods containing less um for cats with chronic kidney disease, lower urinary tract dis-
sodium (0.48 to 0.77 mg sodium/kcal; 0.19 to 0.31% DM, for orders and other conditions (e.g., hypertension) is unknown.
a food with 4 kcal ME/g DM) was associated with calcium One study revealed that six cats with early kidney disease had
oxalate uroliths in cats (Lekcharoensuk et al, 2001a). Despite significant increases of serum creatinine, urea nitrogen and
this finding, feeding a veterinary therapeutic food containing phosphorus when consuming a food with 1.2% DM sodium
0.67 mg sodium/kcal (0.27% DM for a food with 4 kcal ME/g for three months vs. when fed a food with 0.4% DM sodium
DM) to calcium oxalate urolith-forming cats was associated (Kirk et al, 2006). Additional evaluation of effects of increased
with a significant decrease in urine calcium excretion and calci- sodium intake is needed because most studies have either been
um oxalate saturation compared with eating their regular food of short duration (<6 months) or were performed in healthy
(Lulich et al, 2004). The recommended range for dietary sodi- cats. Pending availability of additional data (e.g., effects of high
um intake in cats at risk for calcium oxalate uroliths is 0.3 to sodium intake in cats with calcium oxalate uroliths), orally
0.6% DM sodium. administered sodium chloride should be used cautiously and
Varying levels of sodium have been used in foods f,g that with careful monitoring because of the potential for increased
have been shown to be effective for struvite dissolution in risk of calcium oxalate urolith formation in some patients
feline patients (Osborne et al, 1990; Houston et al, 2004). In (Bartges and Kirk, 2006).
lieu of other data, based on the sodium levels in these foods, a
recommended range for sodium content for foods for struvite Urinary pH
dissolution could be developed by simply bracketing the levels The kidneys eliminate acid that is produced as a result of nor-
in these foods (e.g., 0.37 to 1.27% DM sodium). However, mal metabolism, including digestion of food. Therefore, to