Page 53 - Small Animal Clinical Nutrition 5th Edition

Macronutrients 53

without food. Under normal circumstances, thirst ensures that
Box 5-2. Measuring Water Intake in
VetBooks.ir water intake reduces food intake, which reduces production in Dogs and Cats.
water intake meets or exceeds the requirement. Inadequate
Daily water intake in dogs and cats can be measured easily with
dogs and cats (growth, lactation, reproduction and physical
activity). Decreased water intake may result from reduced avail- common household tools. The following steps should allow pet
owners to obtain a reasonable estimate of daily water intake.
ability, water temperature extremes or poor quality. Water
1. Determine daily water intake requirements (in ml) by calcu-
intoxication (over consumption) is extremely rare in normal,
lating the resting energy requirement of the animal and
healthy dogs and cats but can be induced in animals offered
multiplying by 1.6 for dogs and 1.2 for cats.
water free choice after prolonged dehydration. 2. Using a fluid cup measure (1 cup = 227 ml), measure the
amount of water to offer the animal throughout the day in
a single container.
ENERGY 3. Fill the water bowl with an appropriate amount of water
from the single container throughout the day, ensuring
Definition fresh water is available at all times.
Living organisms need energy to fuel all bodily functions. The 4. Eliminate the animal’s access to other water sources (e.g.,
toilet bowls, sinks, etc.).
ultimate source of all energy is the sun, which enables plants to
5. If more water is needed beyond the calculated amount,
make energy-containing nutrients from carbon dioxide and
carefully measure more water into the container and
water through photosynthesis (Figure 5-5). A key function of
account for the additional amount when making intake cal-
dietary intake is to provide energy. Animals eat plants or other
culations.
animals that have eaten plants. Although energy itself is not a 6. Measure the water remaining at the end of the day (sum of
nutrient, fats, carbohydrates and amino acids contain energy in that remaining in the water bowl and container) and deter-
the form of chemical bonds and are the energy-containing mine the amount of water consumed by subtracting the
nutrients in food. Once eaten, these nutrients are digested, remaining water from the total amount measured during
absorbed and transported to body cells where they are used to the day.
generate energy.
Burning nutrients and measuring the amount of released
heat can determine their energy content. The body obtains
energy by oxidizing nutrients to carbon dioxide and water, but ATP are approximately 90, 75 and 55% for fat, carbohydrate
does not use heat for fuel directly, although heat is used for and protein oxidation, respectively (Flatt, 2001). Biochemical
body temperature regulation. Instead, the body captures nutri- reactions that occur in glycogen synthesis, fatty acid synthesis,
ent energy in energy-containing compounds through a series of protein synthesis, gluconeogenesis, protein turnover, Cori cycle,
enzymatic biochemical reactions. The most important energy- sodium-potassium ion pump, ureagenesis and muscular con-
containing compound is ATP. tractions all require ATP.
In nutrition, the joule is the internationally recognized unit In summary, animals use energy for pumping ions, molecu-
of measure for energy (Kleiber, 1972; Blaxter, 1989). The joule lar synthesis and to activate contractile proteins (Figure 5-5).
expresses the DER of an animal by its power needs or watts. These three processes essentially describe the total use of ener-
One watt equals one joule per second. In the United States, a gy by animals. Without energy supplied by food, these reac-
more commonly used energy measure is the calorie, which tions would rapidly cease and death would occur.
expresses energy in terms of heat. A calorie is the amount of
heat required to raise the temperature of 1 g of water from Importance of Energy in the Diet
º
º
14.5 C to 15.5 C. A kcal is 1,000 calories and a kilojoule (kJ) of Dogs and Cats
is 1,000 joules. Kcal and kJ can be interconverted using the for- The energy content of a food ultimately determines the quan-
mula 1 kcal = 4.184 kJ. tity of food that is eaten each day and therefore affects the
amount of all other nutrients that an animal ingests. Animals
Function should be fed enough food to meet their energy requirements
The biochemical reactions that take place in the body either use and the non-energy nutrients in the food should be balanced
or release energy. Anabolic reactions require energy and, con- relative to energy density to ensure adequate nutrient intake.
versely, catabolic reactions release energy. ATP and other ener- Animals eating an energy-dense food consume less of the food
gy-trapping compounds pick up part of the energy released to meet energy needs; therefore, the concentration of other crit-
from one process and transfer it to the other process. For exam- ical nutrients must be higher to ensure sufficient intake.
ple, in the oxidation of nutrients (glucose, fatty acids and amino Conversely, animals must consume more of a low-energy food
acids), the chemical reactions in the biochemical pathways of to meet energy needs. Therefore, the concentration of non-
glycolysis, β-oxidation, deamination, tricarboxylic acid (TCA) energy nutrients should be lower to avoid excessive intake and
cycle and oxidative phosphorylation simultaneously generate maintain nutrient balance. If the energy density of the food is
and consume ATP. However, the net effect of these reactions is too low, food intake may be restricted by the physical limita-
generation of ATP. It has been estimated that the net yields for tions of the gastrointestinal (GI) tract. Such a food is referred