Page 51 - Small Animal Clinical Nutrition 5th Edition

Macronutrients 51

As animals mature, they require proportionately less water on
VetBooks.ir a weight basis because they consume less food per unit of body
weight; thus, there is less urinary water loss. In addition, adult
animals have less surface area per unit of body weight resulting
in less evaporation from skin.

Water Quality
Salinity, nitrates and nitrites, toxic organic and inorganic
chemicals and microbial contamination can affect water qual-
ity. Routine measurement of water quality is the concentra-
tion of all constituents dissolved in water, referred to as “total
dissolved solids” (TDS). Salinity (salt content of water) is syn-
onymous with TDS as an indication of the total ionic concen-
tration in fresh water. Water containing less than 5,000 parts
per million (ppm or mg/l) TDS is generally considered
acceptable for consumption, whereas water containing more
than 7,000 ppm is considered unsuitable for livestock or poul-
try (NRC, 1974). Although livestock and poultry TDS values
are assumed to apply to dogs and cats, water containing less
than 500 ppm TDS is considered acceptable for human
drinking water and is a better recommendation for dogs and
cats (US EPA, 1976).
Standard water quality testing (e.g., nitrates, sulfates, bacter-
ial contamination) typically can be addressed through local
Figure 5-3. Proximate analysis of foods.
public health departments because the source of water con- *Proteins contain 16 ± 2% nitrogen. Crude protein = nitrogen x 6.25
sumed by dogs and cats is often the same as that consumed by or nitrogen ÷ 0.16. Protein levels determined by this method will be
people. Serious concerns about water quality (toxic inorganic erroneously high if the food contains non-protein nitrogen such as
chemicals or pesticides) need to be addressed through testing at urea or ammonia.
commercial analytical laboratories capable of screening water **Frequently called nitrogen-free extract (NFE). NFE is determined
for pesticide residues and other chemicals. as the difference between 100% and the amount of everything else
in the food (i.e., 100% – % moisture – % crude protein – % fat – %
Mineral Content crude fiber – % ash.) Any errors in these analyses also will appear
in the NFE value.
Water “hardness,” or the sum of calcium and magnesium salts
in relation to calcium carbonate, has little effect on dog or cat
well being. High levels of magnesium in hard water have been
implicated as a cause of urolithiasis in cats; however, the
amount of magnesium consumed in drinking water is insignif-
icant compared with the amount consumed in food (i.e., usual-
ly a 10,000-fold difference) (Kirk et al, 1995). Cats prone to
urolithiasis may benefit from consumption of distilled water
rather than hard water that has been softened with a sodium
chloride water softener.
Figure 5-4. Electron transport chain and metabolic water produc-
tion. Key: NAD = nicotinamide-adenine dinucleotide, NADH = the
Nitrates
reduced form of NAD, Fe = iron, H O = water, O = oxygen, H/H 2
2
2
Nitrates are widely dispersed in the environment and can be a = hydrogen, A = metabolite, Fp = flavoprotein.
health hazard for all animals when significant amounts are
present in drinking water. Although the concentration of
nitrate ions (NO ) commonly found in drinking water is well safe upper limits for nitrate and nitrite determined for live-
3
tolerated by dogs and cats, nitrite (NO , the reduced form of stock drinking water are 1,320 ppm and 33 ppm, respectively.
2
nitrate) is readily absorbed and can be toxic. At toxic levels, For human drinking water, the safe upper limit is based on the
nitrites oxidize iron in hemoglobin to form methemoglobin, total amount of nitrogen derived from the combination of
reducing the oxygen-carrying capacity of blood. nitrate (30.4% nitrogen) and nitrite (22.6% nitrogen) and is
Frequently, nitrates in the water supply indicate bacterial 10 ppm of nitrogen. No safe upper limits have been estab-
contamination. Bacterial reduction of nitrate to nitrite is pro- lished for dogs or cats. The livestock limits should be used
moted as the pH increases in the intestinal tract. Bacteria in until studies are conducted to determine the upper limits for
contaminated water sources can convert nitrate to nitrite.The dogs and cats.