Page 58 - Small Animal Clinical Nutrition 5th Edition

58 Small Animal Clinical Nutrition

an animal is in a thermoneutral environment, heat production
Box 5-3. AAFCO Protocol for Determining
VetBooks.ir Metabolizable Energy of Dog and Cat results from basal cellular metabolism. In this case, the term
basal energy expenditure (BEE) can be used as an alternative to
Foods.
heat production. Thus, when heat production is measured,
Animal feeding studies are the most desirable means for meas- energy expenditure is measured, and then energy expenditure is
uring the metabolizable energy (ME) of a food. The following equated with energy requirements. Also, if energy retention is
steps summarize what is involved when investigators conduct zero, then an animal is in energy equilibrium where heat pro-
a ME study using dogs or cats, according to protocols estab- duction equals ME. In this case, ME equals NE . The third
m
lished by the Association of American Feed Control Officials term can be derived if two of the three terms of the energy
(AAFCO). budget equation are known. Alternatively, if all three compo-
1. Feed a group of animals a known amount of food each
day for a given number of days (typically five to seven days nents are measured then there is added confidence in the ener-
for dogs and between five and 15 days for cats). gy requirement estimate.
2. Collect and record the weight of feces excreted on the Laboratory protocols and specialized equipment have been
same days as food measurements were made. developed to measure the three major components of the
3. Analyze the gross energy (GE) content of samples of the energy budget. ME determinations have been discussed pre-
food and feces (FE) by bomb calorimetry. Bomb calorime- viously. Box 5-4 provides information about whole animal
try involves placing a known amount of the food or feces calorimetry used to estimate HI. The primary forms of RE in
into a bomb compartment submerged in a water bath. animals are protein and fat, although a small and relatively
Oxygen is added to the compartment and ignited with an constant proportion of carbohydrate is stored as glycogen.
electrical spark and the increase in water temperature The gold standard method for measuring RE in farm animals
that surrounds the bomb is measured as the sample is the comparative slaughter method in which the energy con-
burns. Urinary energy (UE) can be measured directly by
collecting urine and then determining the GE of the urine. tent of an animal is determined by bomb calorimetry on
Alternatively, measuring protein digestibility and then ground carcass samples (McDonald et al, 1995). Other meth-
using a factor that predicts the energy content of the urine ods have been developed that are noninvasive, less costly and
can estimate UE. Energy from intestinal gases is typically allow for repeat measurements on the same subject.
ignored because it constitutes a very small proportion of Underwater weighing, bioelectrical impedance, anthropomet-
energy lost in dogs and cats. ric measurements (triceps skin-fold thickness, upper arm
4. ME of the food is then calculated as GE minus FE and UE. muscle area and body mass index), stable isotopes, zoometric
measurements, ultrasound and dual energy x-ray absorptiom-
The Bibliography for Box 5-3 can be found can be found at etry [DEXA]) are commonly used to estimate body composi-
www.markmorris.org. tions (fat and lean proportions) of people and other animals.
Some of these methods have been further adapted for use in
dogs and cats. Two-dimensional ultrasound technology has
been used successfully for estimating back fat and total body
mal including: 1) energy consumed in food, 2) energy losses fat to determine obesity in dogs (Morooka et al, 2001;
from the body via urine, feces and intestinal gases, 3) heat pro- Wilkinson and McEwan, 1991; Anderson and Corbin, 1982).
duced by metabolism and/or physical work, 4) retention of In recent years, DEXA technology has been used to provide
energy as tissue accretion and 5) secretion of energy as milk rapid and repeatable estimates of body composition of dogs
(Blaxter, 1989). Because the first law of thermodynamics states and cats (Wedekind et al, 1992; Toll et al, 1994).
that energy is conserved, energy intake by the animal minus all For animals under maintenance conditions, when no tissue
energy lost must equal the energy retained or secreted as shown is accreted or milk secreted, the RE component of the energy
by the following equation: balance equation is theoretically zero; therefore, the HI is the
RE = GE – FE – UE – GPD – HP estimate of the energy expended for maintenance of adult ani-
(Where GE = gross energy intake, FE = fecal energy excreted, mals. In growing, pregnant and lactating animals, the RE por-
UE = urine energy excreted, GPD = gaseous products of diges- tion of the energy budget is not zero; therefore, both the RE
tion, HP = heat production and RE = retained energy primari- and HI should be measured to accurately predict the energy
ly in the form of lean and fat tissues or energy secreted in milk). requirements for animals undergoing these production
The above equation can be simplified to three terms by substi- parameters.
tuting ME for the GE – FE – UE – GPD portion of the equa- Energy requirements have been given different names
tion. The simplified energy budget equation is now: depending on the physiologic and environmental conditions
RE = ME – HP under which the measurements were made (Table 5-1). Basal
Heat production is the sum of heat lost through radiation, energy requirement (BER) represents energy needs for a nor-
convection, conduction and evaporation and heat stored in the mal, awake, fasting, resting animal in a thermoneutral envi-
body as exemplified by an increase in body temperature. Heat ronment. For dogs and cats, fasting overnight or for 12 hours
is lost when food is metabolized and when physical work is per- is usually considered adequate. BER includes the energy
formed. When no food is given, no physical work is done and needed to maintain cellular activity, respiration and circula-