Page 116 - Small Animal Clinical Nutrition 5th Edition

Minerals and Vitamins 117

added to pet foods include potassium citrate, potassium chlo- hyperthyroid disease or obesity. Pet food manufacturers some-
VetBooks.ir ride and potassium sulfate. times use dietary salt supplementation to increase water intake
in cats with lower urinary tract disease. High sodium intake in
Sodium and Chloride
the short term effectively increases water intake, urine output
Sodium and chloride, in addition to potassium, are important and urine dilution, thus lowering the risk of urolithiasis, but
for maintaining osmotic pressure, regulating acid-base equilib- may have detrimental effects in the long term. Kirk (2002)
rium and transmitting nerve impulses and muscle contractions showed that high-sodium intake (1.1% DM) over a three-
via Na-K-ATPase (sodium pump). In addition, sodium and month period, increased serum urea nitrogen, phosphorus and
chloride control the passage of nutrients into cells. Sodium ions creatinine concentrations in cats with preexisting renal disease.
must be present in the lumen of the small intestine for absorp- In addition, the high-sodium food increased cardiac left ven-
tion of sugars and amino acids. Insufficient sodium concentra- tricular fractional shortening and lowered plasma aldosterone
tions decrease the use of digested protein and energy. Sodium levels, evidence suggesting that this sodium chloride load
also influences calcium absorption and mobilization and may required both the heart and kidney to work harder. Similarly,
affect absorption of several water-soluble vitamins (e.g., both the NRC Mineral Tolerance of Animals (2005) and the
riboflavin, thiamin and ascorbic acid) that are sodium coupled NRC Nutrient Requirements of Dogs and Cats (2006) recom-
(McDowell, 1992). mend a safe upper limit for sodium at 1.5% DM for adult dogs,
Sodium and chloride are readily absorbed, principally from and 1.0 and 1.5% DM for kittens and adult cats, respectively.
the upper small intestine, and excreted predominantly in the At higher levels of sodium intake (≥2%), studies showed
urine with smaller amounts in feces and perspiration. Marked reduced food intake, negative potassium balance and vomiting.
losses of salt can occur through perspiration in some species, In the absence of studies establishing chloride requirements
secretion in milk, vomiting and diarrhea. When sodium intake for dogs or cats, the DM recommendation for chloride is 1.5
is inadequate, the body has a remarkable capacity for conserv- times that of sodium. This value is comparable to the Na:Cl
ing sodium by excreting extremely low levels in the urine. requirement ratio for other species. Table 6-1 describes signs of
Chloride metabolism is controlled in relation to sodium. For deficiency and excess (Case 6-1).
example, excess urinary excretion of sodium is accompanied by The effect of dietary sodium chloride on blood pressure has
urinary excretion of chloride. generally been attributed to the sodium ion. However, it is clear
Hormones acting to maintain a constant sodium-potassium from a number of studies that both sodium and chloride are
ratio in extracellular fluid regulate sodium concentrations in the necessary to inhibit renin production (Kotchen et al, 1978;
body. Aldosterone, secreted from the adrenal cortex, regulates Kurtz et al, 1987). Salts such as sodium chloride, potassium
reabsorption of sodium from the renal tubules. Antidiuretic chloride, lysine hydrochloride (but not lysine glutamate, sodi-
hormone from the posterior pituitary responds to osmotic pres- um bicarbonate, potassium bicarbonate) inhibited renin pro-
sure changes in the extracellular fluid. Both hormones maintain duction in sodium chloride-deprived rats and people.
a constant sodium-potassium ratio. Fish, eggs, dried whey, poultry by-product meal and soy iso-
A number of factors influence the sodium requirement. The late are ingredients high in sodium and chloride. Sodium
requirement is increased during reproduction, lactation, rapid and/or chloride supplements typically added to pet foods
growth and heat stress and with high dietary potassium levels. include salt, sodium phosphates, calcium chloride, choline
In people, the average sodium intake exceeds the recommend- chloride, potassium chloride and sodium acetate.
ed requirement by 15-fold (Stamler, 1995). Likewise, the sodi-
um content of certain pet foods exceeds the recommended level Microminerals
by four- to 15-fold (Chapter 36). Investigators determined the Iron
sodium requirement of kittens to be 0.16% (DM or 0.30 mg Iron is present in several enzymes and other proteins responsi-
Na/kcal ME) based on aldosterone concentration in plasma ble for oxygen activation (oxidases and oxygenases), for electron
(Yu and Morris, 1997). The same investigators determined the transport (cytochromes) and for oxygen transport (hemoglobin,
requirement for adult cats was 0.08% DM sodium or 0.15 mg myoglobin). Because of the limited capacity of the body to
Na/kcal ME (Yu and Morris, 1999).The AAFCO (2007) rec- excrete iron, iron homeostasis is maintained primarily by
ommendation for sodium in cats is 0.2% DM for both adjusting iron absorption. Iron in foods exists in two forms: 1)
lifestages, whereas in dogs, the recommendation is 0.3% DM heme iron present in hemoglobin and myoglobin and 2) non-
for growth and reproduction and 0.06% DM for adult mainte- heme iron present in grains and plant sources.
nance. The current NRC (2006) sodium recommendation is Heme iron absorption is not greatly affected by iron status or
0.14% DM for kittens and 0.068% DM for adult cats. The other dietary factors. (Two exceptions are meat, which
NRC (2006) suggests a 0.22% minimum DM sodium require- enhances heme iron absorption, and calcium, which inhibits
ment for puppies and 0.08% DM for adult dogs. heme and nonheme iron absorption.) In contrast to absorption
High sodium intake has long been reported to increase the of heme iron, absorption of nonheme iron is markedly influ-
risk of hypertension in people and animals (Stamler, 1995). Pet enced by iron status and by several dietary factors such as phy-
populations with increased risk of hypertension include senior tate, tannins and excesses of calcium, phosphorus, manganese,
dogs and cats and those with renal disease, cardiac disease, zinc, copper and ascorbic acid (Hallberg and Rossander-