Page 31 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

20 APPLIED PHYSIOLOGY

340
TABLE 1-11 Ratios of Total Water to
Dry Matter in Cat
300
Foods
Canned Semi-
Cat moist Cat Dry Cat
Investigator Foods Foods Foods
Water intake (ml/day) Thrall and 3.7 2.0-2.4 {
200
58
Miller
2.8,* 2.3
Jackson and
3.2
Tovey
Holme 23 24 5.6 2.8 2.4
100 Seefeldt and 3.9 2.3
Chapman 53
Jenkins and 2.9 1.8 1.8
Coulter 24a
Data from DiBartola SP, Buffington CA. Feline urologic syndrome. In:
Slatter D, editor. Textbook of small animal surgery. Philadelphia: WB
Food type CC b DC a DC ac DC bc SMC abc Saunders, 1993: 1473–1487.
Salt content 1.6 1.3 3.6 4.6 3.7 *Expanded.
(% D.M.) {
Figure 1-10 Effects of food type and salt content on water intake Nonexpanded.
in cats. Each column represents the total daily water intake (mean
SD) for cats on various diets. The same group of six cats was used
for all foods except a DC diet 4.6% salt, data for which were
obtained from a different experiment using another group of 12 cats. The solute load of the diet also influences water drink-
The solid area shows food water, and the clear area shows water ing. Approximately two thirds of the renal solute load is
drunk. Total water intake for foods bearing different superscript urea, an end product of protein metabolism, and increas-
letters is significantly different (P <.05, Student t test). CC, canned; ing the protein content of the diet increases the renal sol-
DC, dry; SMC, intermediate moisture food. (From Burger IH, ute load. Diets higher in protein also are associated with
Anderson RS, Holme DW. Nutritional factors affecting water greater total water intake. The ions Na ,K ,Ca ,
þ
2þ
þ
balance in the dog and cat. In: Anderson RS, editor. Nutrition of the Mg 2þ ,PO 4 3 ,Cl , and SO 4 2 also contribute to dietary

dog and cat. Oxford, UK: Pergamon Press, 1980: 151.) solute. Increasing percentages of salt in foods are
associated with increased water intake in both cats and
dogs. 6,22 This principle has been exploited to increase
50 cc/KG voluntary water consumption in cats that are fed dry food
Drinking water 25 diets and are at risk for developing lower urinary tract
disease.

No food Male METABOLIC WATER
Female
0 Metabolic water contributes approximately 10% to 15%
0 2 4 6 8 10 12 14 16 18 20
of total water intake in dogs and cats, depending on
Days 4
Figure 1-11 Comparison of composite drinking curves of male the diet. Nutrients differ in their yield of metabolic water
and female dogs during alimentation and food deprivation. Each (Table 1-12). Although fats provide the most water per
curve is the composite of 10 experiments. (From Cizek LJ. gram, carbohydrates provide the most water per calorie
Long-term observations on the relationship between food and and per liter of oxygen. 3,9 Therefore, high-carbohydrate
water consumption in the dog. Am J Physiol 1959;197:342–346.) diets spare the water requirement by providing more met-
abolic water per calorie. Carbohydrates and fats also spare
3
water loss because they do not generate renal solute. The
prevention of lower urinary tract disease. 4,22 The ratio of volume of metabolic water generated per day in humans,
total water to dry matter is an index of the moisture con- and by inference in dogs and cats, is relatively small com-
tent of the food and of the cat’s drinking response to that pared with the total daily water intake. 12 Metabolic water
diet. As predicted, canned foods have higher ratios than is difficult to quantitate in the clinical setting, and many
dry foods (Table 1-11). Although cats drink more when studies ignore its contribution to water homeostasis.
consuming dry instead of canned foods, their total water Definitive water balance studies should include evalua-
intakes are usually lower with dry than with canned foods. tion of metabolic water. 52