Page 52 - Small Animal Clinical Nutrition 5th Edition

52 Small Animal Clinical Nutrition

nitrates and phosphates. Generally, if levels of these compounds
Box 5-1. The Effect of Fasting on Water are high, the bacterial level will also be high.
VetBooks.ir Intake: Diagnostic Implications. Water Requirements
Fasting eliminates water available from food, alters the amount
an animal drinks and decreases total water intake. Figure 1 Water requirements are related to maintaining water balance.
shows the effect of fasting on drinking water intake, water intake Body water lost by urination, defecation, evaporation and per-
from food and total water intake for dogs previously consuming
moist or dry food. Total water intake decreased dramatically in spiration is replaced by one of two sources: 1) water derived
both groups; however, the change in the amount consumed as from metabolism of nutrients and 2) water consumed as a liq-
drinking water was quite different. Figure 1, Panel A shows the uid or as a portion of the food.
response of dogs previously fed a moist food. Because most Oxygen is the final acceptor of hydrogen ions cleaved from
water intake for these dogs previously was from the food, only a energy-supplying nutrients (carbohydrates, fats and proteins)
small amount was supplied by drinking water. During fasting, during the generation of adenosine triphosphate (ATP)
water supplied by food was no longer available, thus the amount (Figure 5-4). This combination of hydrogen and oxygen is
drunk increased. Figure 1, Panel B shows the response of dogs called metabolic water. Metabolic water can account for 5 to
previously eating a dry food. Because these dogs obtained little 10% of the total water requirement. An average of 13 ml of
water from the food, a large amount was supplied from drinking water is produced per 100 kilocalories (kcal) of metabolizable
water. During fasting, less water was needed and the amount of energy (ME) ingested (Anderson, 1982). Oxidation of 1 g of
drinking water consumed decreased.
The influence of the water content of the previous food on the glucose, fat and protein results in the production of 0.556,
amount of water consumed as drinking water may become 1.071 and 0.396 g of metabolic water, respectively (Schmidt-
important diagnostically. An owner who reports that a dog is not Nielsen, 1964).Three to 4 g of water are released per g of glyco-
eating but is drinking twice as much water may be describing the gen used (Gosolfi, 1983).
normal response of a dog that has stopped eating a moist food, Dogs and cats meet most of their water requirement through
rather than a dog that is truly polydipsic. Conversely, dogs that water ingested as food or drink. Animals consuming commer-
had been eating dry food may appear to nearly stop drinking dur- cial moist foods drink less liquid than those fed dry foods
ing periods of anorexia. These effects emphasize the importance because of the higher water content of moist foods (>75%
of accurately assessing the food and feeding method. water). This finding may have important diagnostic implica-
tions (Box 5-1). Generally, the daily water requirement of dogs
The Bibliography for Box 5-1 can be found can be found at and cats, expressed in ml/day, is roughly equivalent to the daily
www.markmorris.org. energy requirement (DER) in kcal/day (for dogs 1.6 x resting
energy requirement [RER]; for cats 1.2 x RER) (Harrison et al,
1960; Haskins, 1984). The amount of water consumed by
mature, healthy, nonreproducing dogs and cats at a comfortable
environmental temperature is about 2.5 times the amount of
dry matter (DM) consumed as food.
Domestic cats, descendants of desert animals, normally
form more concentrated urine than dogs.Thus, water require-
ments for cats may be less than that for dogs. The need for
water can be met by supplying clean, fresh water to pets at all
times (Box 5-2).

Factors Affecting Water Requirements
Although the daily water requirements of dogs and cats are well
defined, practical estimates of daily water intake are less clearly
Figure 1. Effect of fasting on the amount of water consumed in
the food and drunk by beagles previously consuming moist or understood. In addition to metabolic needs, animals of all sizes
dry foods. consume water to meet a variety of needs, including physical
and social. Factors such as body size (surface area), lactation,
ambient temperature, type and amount of food ingested, gen-
eral state of health, stress, water losses through excretion or
Bacteria evaporation and individual animal differences influence the
The accepted criterion for the sanitary quality of water for peo- absolute requirement for water.
ple has been the absence of coliform bacteria. Although all col-
iform bacteria are not pathogens, many possess the potential; Water Deficiency and Excess
their presence indicates water is able to support infectious bac- Deficits of more than a few percent of total body water are
teria or viruses. Results of other qualitative tests made on water incompatible with health, and large water deficits (i.e., 15 to
samples can also predict the presence of bacteria. Bacteria pro- 20% of body weight) lead to death. Water deprivation can lead
portionally accompany chemical compounds such as nitrites, to death within days, whereas animals may survive for weeks