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OCR for page 51
Nutritional
Err.
ITIClenCy
Efficiency is the comparison of output to input. There are numerous schemes
for measuring efficiency of converting ingested foodstuffs to animal product.
For livestock, total (gross) efficiency is calculated as follows:
Total efficiency = Total output x 100
Total input
The most common "feed efficiency" term used by stockmen relates weight
of feed ingested to weight of animal product output (feed to gain ratio) and
may at times be confusing because it relates weights that in essence are not
really comparable. For example, dry matter content of both feedstuffs and
animal product are highly variable, which may result in from 3 to 25 units of
feed by weight required to produce a unit of body weight gain. However,
feed to gain ratio is an accepted way of describing total efficiency and is a
useful term in practical situations since ultimately it is weight of feed that
must be grown or purchased and fed and weight of product sold.
It is more meaningful when relating environment and efficiency to calcu-
late total efficiency in caloric terms to obtain an energetic efficiency term as
shown below:
. . Total energy gain (RE)
Total energetic efficiency =
Total energy intake (lE)
x 100.
Partial efficiency is defined as the observed change in gain for a given
change in feed intake expressed as a percentage:
51
OCR for page 52
52
FARM ANIMALS AND THE ENVIRONMENT
Partial efficiency = /`Energy gain (RE) X 100
Synergy intake (lE)
Since by definition, gains do not occur at or below maintenance, the main-
tenance level of feeding can be used as a baseline from which to calculate
partial efficiency:
Partial efficiency =.
Gain (RE) X 100.
Intake (TE) - Maintenance (HE)
Partial efficiency is simply the ability to convert the energy surplus above
maintenance to stored chemical energy in terms of growth or product. Ani-
mal gains can vary considerably depending on the fat:protein ratio; thus effi-
ciency of energy retention (partial efficiency) will vary with composition of
gain since the cost of fat synthesis is different than protein. When the effi-
ciency of producing product from energy surplus to maintenance (partial effi-
ciency) is altered, then total efficiency is also affected. Some data suggest a
lipogenic effect of cold (Fuller and Boyne, 1971), while other studies
(Hacker et al., 1973) suggest leaner carcasses during cold exposure. Magni-
tude of cold and availability of food are major determinants of composition
of growth for animals. exposed to thermal stress. Seasonal variation in com-
position of expelled product such as butterfat content of milk are well
known. However, when all factors are considered, environment has little ef
fect on partial efficiency.
Changes in total efficiency do not infer changes in partial efficiency. Gen-
erally, environment influences total efficiency by affecting rates of intake
and maintenance energy requirement. Adverse environments alter the effi-
ciency of converting foodstuffs to animal product and therefore are economi-
cally important to study. The fact that climatic environment alters the rela-
tionship of output per unit input has led to varied studies designed to describe
effect of environment or environmental modification on efficiency of con-
verting feed to product. Henderson and Geasler (1969) summarized several
studies comparing the value of modifying both summer and winter environ-
ments with natural environments for the beef cattle studies. In general, for
the locations included in the studies, environmental modification resulted in
improved efficiency of feed conversion although economic advantage was
not always positively correlated with efficiency.
For specific effects of climatic factors several workers have reported de-
creased feed efficiency of swine exposed to either heat (Hazen and Mangold,
1960; Jensen, 1971) or cold (Fuller and Boyne, 1971; Mangold et al., 1967),
although there is some evidence that finishing hogs exhibiting compensatory
OCR for page 53
Nutritional Efficiency
53
growth after removal from heat stress are as efficient as nonstressed animals
(Hahn et-al., 1975~. Ames and~Brink (1977) reported reduced feed efficiency
for lambs.exposed to either'heat or cold when compared with thermoneutral-
ity for temperatures ranging from - 5 to 35°C when estimated lower critical
temperature was 159C. Again both heat and cold result in reduced efficiency
of milk production ('McDowell et al., 1976) when compared as kilograms of
milk per megacalorie feed-energy. Under heat stress, feed efficiency (mega-
calories of ME per kilogram of milk) declines rapidly above 27°C (Moody et
al., 19671.
An example of an environmental effect on rate of performance and ener-
getic efficiency of food animals is illustrated by data shown in Table 11 col-
lected from similar swine grown in temperatures ranging from cold stress
(0°C) to heat stress (35°C). The energetic efficiency was reduced during both
cold and heat stress and was highest during the TNZ. While the temperature
and efficiency values may differ for animals with different insulation, diets,
etc., or for different species and products, the same general pattern of re-
duced energetic efficiency is consistent among animals exposed to stressful
environments. This reduced energetic efficiency, in turn, causes an eco-
nomic loss. Livestock producers are usually willing to incorporate manage-
ment systems to improve energetic efficiency when that is advantageous eco-
nomically.
There are some reports (Holme and Coey, 1967; Sugahara et al., 1970) of
improved efficiency of swine during mild cold compared with thermoneutral
conditions. Figure 16 suggests this may happen if rate of increased voluntary
intake is more rapid than rate of increased energy requirement for heat pro-
duction during cold. When exposed to heat, the combination of reduced in
TABLE 11 Effect of Temperature on Intake, Growth Rate, and Efficiency
of Energy Conversion for Swine (70 to 100 kg)
Temperature Caloric Intake Growth Rate Product Caloric
( C) (kcal DE/day) (kg/day) (kcal GE)a Efficiency (%)b
0 15,377 0.54 2,991 19.4
5 11,404 0.53 2,936 25.7
10 10,616 0.80 4,432 41.7
15 9,554 0.79 4,376 45.8
20 9,766 0.85 4,709 48.2
25 7,976 0.72 3,988 50.1
30 6,703 0.45 2,493 37.1
35 4,579 0.31 1,717 37.4
a Estimated caloric value of gain for an 80-kg pig is 5.54 kcal GE/g (Thorbeck, 1975).
b Calculated: (kcal GE in product . kcal DE intake) x 100.
SOURCE: Ames, 1980.
OCR for page 54
54
FARM ANIMALS AND THE ENVIRONMENT
LOT UCT
\
\
-
I
-
UJ
at
-
RE
Cold
TNZ
>(
Heat
EFFECTIVE AMBIENT TEMPERATURE (EAT)
FIGURE 16. Schematic relationship of heat production (HE), intake en-
ergy (lE), and energy for production (RE = lE - HE) with temperature
zones.
take and increased heat production result in reduced efficiency for growing
animals.
In contrast to most data for growing animals, total energetic efficiency of
producing expelled products such as eggs and milk have been reported to be
improved during heat by Davis et al. (1972) and Johnson (1965), respec-
tively. This apparent difference in efficiency of an expelled product com-
pared with tissue growth is explained by catabolism of body stores to meet
energy demands during heat when intake is reduced. (See page 112 for a de-
tailed description of energetic efficiency of egg production). Consequently,
caloric efficiency of producing an expelled product is improved primarily be-
cause of mobilization of tissue reserves while only ingested energy is used to
calculate caloric efficiency. Of course, original costs of depositing depot fat
are not considered, and, therefore, caloric efficiency of producing an ex-
pelled product such as the egg during heat must be taken within the context
of short-term utilization of stored energy. Conversely, catabolism of tissue
stores in animals where growth is the end point of production is self-
defeating and results in lowered efficiency, although a lower percent carcass
fat may be considered a desirable result. There may, however, be instances
of management systems that rely on the ability of animals to withstand per-
iods of reduced feed quantity or quality and then recover tissue stores
through compensatory growth when the diet is more favorable. There appear
to be two additional reasons for improved efficiency of producing eggs dur-
ing heat. First, efficiency of using body fat as an energy source is high com-
pared with using energy from feed sources, which results in higher efficiency
of egg production during heat exposure. And second, van Kampen ( 1974) re
OCR for page 55
Nutritional Efficiency
55
ported lowered HeE, while McDonald (1978) reported lowered "existence
energy" during heat as a result of lowered intake and reduced activity of lay-
ing hens.
Reports of energetic efficiency for animals exposed to fluctuating environ-
ments compared with constant temperature are conflicting. Bond et al.
(1963) found that pigs exposed to a constant 21°C environment had higher
total efficiency than pigs exposed to cyclic 10 to 32°C or 4 to 38°C environ-
ments. Giacomini (1979), working with lambs, and Sorensen and Moust-
gaard (1961) and Hahn et al. (1975), with pigs, found no difference in effi-
ciency of growth when cyclic environments were compared with constant
temperature environments of the same mean temperature. The variety of dif-
ferences in fluctuating environments (i.e., duration, magnitude of change,
etc.) will require much more data before conclusions can be drawn.
Numerous studies suggest that specific climatic variables change total effi-
ciency. Morrison et al. (1966) found no effect of 45, 70, and 95 percent rela-
tive humidity on hogs when temperature was considered optimum, but a sig-
nificant effect was noted when studied during heat (Morrison et al., 1969~.
Berry et al. (1964) reported declines in milk production with an increasing
TH! value. Morrison et al. (1971) indicated lower total efficiency of gain for
cattle exposed to rain but improved total efficiency with wind during mild
winter conditions in California. Further examples of effects of specific cli-
matic variables only substantiate the need to use effective ambient tempera-
ture when relating effects of the climatic environment to performance.
Measurement of efficiency in the short term can lead to erroneous conclu-
sions because of differences in an animal's previous nutritional background.
For example, animals that have received restricted intake will compensate
with improved feed efficiency when allowed ad libitum intake. Hens for-
merly on restricted diets gradually renew their lipid reserves (Polin and
Wolford, 1972) by depositing lipid in the carcass more efficiently than non-
restricted birds. Allden (1968) reported that feed consumption and feed utili-
zation were not affected in the long term following a period of nutrient re-
striction although compensation was observed early in the recovery period.
Searle and Graham (1975) reported no difference in body composition of ani-
mals held at constant weight for up to 6 months by restricted feeding and
then fed ad libitum compared with lambs fed ad libitum. Short-term changes
in efficiency during heat stress may occur, but studies show (Hahn et al.,
1975) that animals convert feed more efficiently after relief from heat stress
compared with unstressed animals subjected to restricted nutrition and tend
to equalize in the long run with little effect on long-term efficiency. Degen
and Young (1980) reported that rapid changes in live weight during and fol-
lowing cold exposure can be largely attributed to losing and gaining of body
fluids.
OCR for page 56
56
FARM ANIMALS AND THE ENVIRONMENT
The impact of climatic environment on energy flow in terms of both en-
ergy intake and that available for growth may directly affect the utilization of
other nutrients because in many cases nutrient requirement is a function of
available energy. For example, protein efficiency ratio (grams of gain per
gram of cP) is lowered during both heat and cold stress in sheep (Ames and
Brink, 1977), and Fuller and Boyne (1971) and Roy et al. (1969) have re-
ported lowered nitrogen retention during thermal stress in swine and cattle,
respectively. These examples emphasize the need to consider available en-
ergy in the light of environmental stress and to adjust rations to enhance effi-
cient utilization of all nutrients.
Representative terms from entire chapter:
energetic efficiency
