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OCR for page 29
~ Water
Water is the single most important nutrient necessary
to sustain normal function of all living cells. The nonfat
component of mammals contains about 73 percent wa-
ter. Most mammals can lose nearly all their reserves of
glycogen and fat, half the body protein stores, and 40
percent of their body weight and survive. However,
mammals are much less tolerant to losses of body water.
Cats can withstand acute dehydration slightly better
than dogs with water losses reaching up to 20 percent of
body weight (Adolph, 1947~. Although cats can tolerate
some depletion of their body water for a short period,
they must in the long run remain in water balance. The
losses of water from the body must be offset by an equal
intake of water. At normal temperatures, water is lost
from the body via the lungs, skin, urine, milk, and feces.
At high temperatures, an additional loss may occur via
saliva, which is used to wet the fur and provide evapora-
tive cooling (Robinson and Lee, 1941~. The body gains
water from "free water" present in liquids and solid
foods and "oxidation water" arising from the catabolism
of carbohydrates, fats, and protein. Oxidation of 1 g of
starch, fat, and protein results in the production of
0.556, 1.071, and 0.396 g of oxidation water, respec-
tively (Schmidt-Nielsen, 1964~.
A number of studies have been conducted in which
the ratio of free water to ciry matter intake of cats has
been measured (Carver and Waterhouse, 1962; Thrall
and Miller, 1976; Holme, 1977; Jackson and Tovey,
1977; Seefeldt ant] Chapman, 1979~. Anderson (1983)
summarized these data and showed that for commercial
dry foods the ratio of water to dry matter intake varied
from 2.0 to 2.8:1 and for canned foods from 3.0 to 5.7: 1.
Kane et al. (1981b), in a study of eating and drinking
patterns of the cat, reported lower ratios of water to dry
matter intake for two purified diets (1.1:1 and 1.4:1)
than those reported by Anderson (1983) for commercial
diets. However, they found similar ratios to those re-
ported by Anderson (1983) for commercial dry and
canned foods (1.9:1 and 3.~:1, respectively). In these
studies cats given dry commercial food ad libitum drank
water about the same number of times as they ate (16.0
versus 15.7 times/day, respectively). All studies on wa-
ter and dry matter intakes of cats indicate higher total
free water to dry matter ratios for cats given commercial
canned food diets than for cats given commercial dry
foods. That is, cats given dry food do not voluntarily
consume water to equal the ratio of water to ciry matter
of cats given canned diets containing about 75 percent
moisture. In satisfying the requirement for energy, cats
consume more water from a canned diet than they
would take in if they were eating an entire small mam-
mal.
The cat is able to achieve a maximal urinary osmolar
concentration much greater than that in man (Schmidt-
Nielsen, 1964), and so is more efficient in conserving
water. Adult cats can maintain normal health in the ab-
sence of drinking, when given high-moisture diets, e. g.,
fresh fish (Prentiss et al., 1959) and can utilize sea water
to facilitate excretion of the urea load from high-protein
diets (Wolf et al., 1959~.
It is recommencled that fresh clean water be available
at all times to cats regardless of their age or diet.
29
Representative terms from entire chapter:
matter intake
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