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OCR for page 27
Feed
Intake
That environmental conditions affect level of voluntary feed intake and the
utilization of the metabolizable energy (ME) ingested is widely accepted, but
it is difficult from existing knowledge to systematically relate environmental
fluctuations to changes in nutritive requirements of animals. Much of the re-
search on changes in feed intake with fluctuations in climatic conditions,
such as temperature, relative humidity, and rate of air movement, have been
conducted under controlled conditions in laboratories usually with only one
variable under study. Most of the laboratory studies have demonstrated
rather dramatic modifications in feed intake at high and low temperatures,
but transfer of this knowledge to farm practice has been difficult mainly be-
cause climatic conditions on farms are considerably more variable than when
evaluated in the laboratory. Those who consider the direct effects of heat or
cold stress on feed intake and performance important for farm feeding should
also be aware of the influence of summer temperatures on changes in forage
quality.
DAIRY COWS
When lactating dairy cows are fed free choice a diet consisting of 60 65 per-
cent Inequality roughage and 35~0 percent concentrates and exposed to
constant temperature conditions, feed intake will increase approximately 35
percent at-20°C over the level at 1~20°C (Figure 5~. Also, lactating cows
under continuous heat stress begin to show a decline in intake a,t>2S-27°C
with remarked decline occurring above 30°C. At 40°C intake is usually no
27
OCR for page 28
28
~ 150
o
o
Cat
4- 125
. _
o 100
-
UJ
~ 75
z
UJ
LL
FARM ANIMALS AND THE ENVIRONMENT
~-
\
\
\
50lLL 1 1 1 1
-20 -10 0 10 20
-
-
\
30 40
TEMPERATURE ( C)
FIGURE 5. Effect of environmental chamber temperature on feed intake in cattle using
1~20°C as baseline (adapted from Johnson et al., 1963; McDowell et al., 1969).
more than 60 percent of the 1 8-20°C level. Rate of feed intake increases dur-
ing cold exposure because it minimizes discomfort from cold (Church et al.,
19744. Efficiency of the utilization of ME for production may actually rise at
temperatures down to-5 or - 10°C but thereafter efficiency declines due to
high rate of heat loss (Williams, l9S94. The rate of rise or decline in feed in-
take at the extremes in temperature is influenced by level of milk yield and to
some extent by breed (Ragsdale et al., 1950, lash.
In general, lactating cows grazing high-quality pastures in either warm or
cool climates and receiving concentrate supplement will tend to have a lower
level of total dry matter intake than when fed a drylot diet of 60 percent
roughage and 40 percent concentrates because of the difference in the water
content of the forages (Yazman et al., 19794. But, when daily maximum
temperature is in the range of 8-22°C, the performance of grazing cows re-
ceiving concentrate supplement at the rate of 1:2 will be nearly equal to that
for cows on the 60:40 diet (Van Soest, 1981~. When maximum daily temper-
ature exceeds 25°C, the rate of dry matter intake from grazing may decline
rapidly due in part to the direct effects of thermal stress on the cow causing
suppression of activity and the indirect decline due to the quality of the for-
age. Frequently, the lowering of forage quality brought about by the effects
of high-temperature conditions on the growth and composition of forages
may be as important, or more so, in determining intake than the direct effects
of thermal stress on the cow. Raising the proportion of concentrates fed to
OCR for page 29
Feed Intake
29
1:1.5 for grazing cows will slow the decline in intake energy with rising tem-
perature but not to the same extent as changing to 80:20 for pen feeding sys-
tems because of a decline in walking to graze caused by the thermal stress
(Yazman et al., 19791.
DAIRY HEIFERS
After about 6 months of age, heifers can at times become fastidious eaters
under almost any environmental conditions; hence, it is difficult to predict
the influence of temperature on their nutritive requirements. Several short-
term studies conducted in a temperature-controlled chamber at the University
of Missouri during the 1950's (Johnson and Ragsdale, 1959) suggested mild
to marked influence of high and low ambient temperatures on the feed intake
and growth rate of heifers. Later, longer-term studies in the same laboratory
showed compensatory growth to overcome short-term growth suppression
from high temperature when the animals were returned to moderate tempera-
tures (Baccari et al., 1980~. Strachan and Marnson (1963), McDowell
(1977), and Yazman (1980) did not find any significant correlation between
ambient temperature during field tests and growth rate over extended periods
(more than 12 months). For example, Yazman (1980) found that during 7-
day periods of above-average ambient temperatures in Puerto Rico average
daily gain declined by 50 percent, but gains following high-temperature per-
iods were 50 to 70 percent greater even though average daily maximum tem-
perature was only 0.5°C lower. Similar behavior has been observed in hot
controlled environment rooms. When dairy heifers were moved from 18 to
29°C, daily gain declined during the first 20 days but recovered during the
second 20 days (Johnston et al., 1961~.
Preliminary results from Maracay, Venezuela, a tropical area, showed that
Holstein heifers on high feeding, but exposed each day throughout life to a
maximum temperature equal to or exceeding 27°C, were 50 kg lighter at 24
months than paternal half-sibs in Maryland even though all heifers were fed
similar levels of energy (C. Schneeberger, Cornell University, personal com-
munication, 19801. The differences in weight for the two locations were not
statistically significant, but the Venezuela heifers were significantly shorter
in length wither to pins ~-3.2 cm) and lower in height at wither ~ - 2.1 cm).
The Venezuelan heifers carried considerably more body fat. The conclusion
was that the high-temperature conditions in Venezuela possibly created an
unidentified imbalance in the utilization of the feeds offered, which may
have affected rate of skeletal development.
Although several laboratory tests (Colditz and Kellaway, 1972) have indi-
cated that heat stress results in smaller changes in feed intake of Bos indicus
heifers than Bos taurus heifers, the percentage decline in both types is ap-
proximately the same.
OCR for page 30
30
FARM ANIMALS AND THE ENVIRONMENT
The general conclusion is that temperature conditions on farms may create
disturbances that will affect efficiency of feed utilization by growing heifers,
but temperature effects are of much less economic significance than for lac-
tating cows or feedlot cattle.
FEEDLOT CATTLE
Generally, growing and fattening cattle have a slightly lower dry matter in-
take per unit of metabolic size than lactating dairy cows, but feeding x tem-
perature interactions appear similar for the two groups (Figure 6 versus Fig-
ure 5~. Estimates of change in feed consumption with temperature by feedlot
cattle were derived from feeding experiments simulating farm conditions.
Complete diets with at least 70 percent digestibility were used. Intake rose
from 10°C to below-10°C in a near linear fashion. Below-10°C variation
among animals was high, possibly because of individual differences in re-
sponse to cold or variation in acclimation, which resulted in large differences
among animals at the same ambient temperature. Although the standard de-
viation for the mean level in intake increased showing high variability among
animals and days, there was a trend for intake to increase to at least-15°C.
In some cases intake declined at the very low EAT because behavioral pat-
terns, such as standing to shiver, caused the animals to spend less time eat-
ing. For instance, under feedlot conditions for mid-winter in Canada daily
gain of steers decreased 70 percent when temperature reached-17°C and ME
intake per unit of gain was 140 percent greater than from March to Novem
125 _
Cal
o
~ 100
oo
Y
A:
Z
_ ~ 75
C:) ~
111 0
o
_
50
B'
1
AD
\0% AD
-20 -10 0 10 20 30 40
TEMPERATURE ( C)
FIGURE 6. Estimated changes in dry matter intake of feedlot cattle on a ration with 70 percent
apparent digestibility or at temperatures above 27°C, 75 percent apparent digestibility. "B" in-
dicates behavioral changes (adapted from Leu et al., 1977; Milligan and Christison, 1974).
OCR for page 31
Feed Intake
31
her (Milligan and Christison, 19741. In this test ADO and feed per unit of gain
had correlations of-0.85 to 0.74 with ambient dry-bulb temperature. The
marked reduction in daily gain indicates both intake and efficiency of utiliza-
tion of ME for gain are lowered.
From 10°C to approximately 25°C there was little change in feed con-
sumption; however, on a 70 percent digestibility diet daily intake declined
rapidly when the cattle were exposed to more than 6 h per day of temperature
above 30°C (Figure 6~. Increasing the energy value of the ration to 75 per-
cent apparent digestibility appeared to help animals maintain intake (Figure
61. Even so, it is more difficult to maintain intake with beef cattle in feedlots
than with lactating cows under extreme temperatures.
There is some evidence from studies with dairy cattle (Ruvuna et al.,
1976) that the appetite of crossbred cows is influenced less by summer heat
stress than for purebreds. With the high use of crossbreeding in the beef in-
dustry, possible advantages of crossbreds in feed efficiency during periods of
stress should receive attention. At 27°C total daily lE of Brahman, Santa
Gertrudis, and Shorthorn heifers was less depressed than that of Brown
Swiss and Holstein heifers (Johnson et al., 19581. The level of intake of the
beef breed heifers was lower, however, both under cool and warm condi-
tions. When change in lE was calculated as percentage at 27°C versus 10°C,
the decline was similar in all breeds, thus species differences for TE resulting
from heat stress are not clearly defined at this time.
The conclusion is that above 25°C and below -10°C type of ration and
level of temperature markedly affect intake but from near O to 25°C digest-
ibility of ration is more important than ambient temperature. Even though
temperature is the environmental variable most frequently associated with
feed intake, lot surface and space per animal and their interaction effects are
also important to feed intake (Elam, 1971; McDowell and Hernandez-
Urdaneta, 19751.
SHEEP
Values for prediction of temperature-feed intake interactions for farm feed-
ing of sheep are limited, mainly because the vast majority of sheep are kept
under extensive grazing conditions. It is well accepted that body covering
(length of fleece) and level of feeding will affect the response of sheep to
temperature conditions (Armstrong et al., 19591. In general, the decline in
feed intake under hot room conditions of unshorn sheep is similar to that for
lactating cows (Figure 5), and shorn sheep respond approximately as do dry
cows.
The values in Table 4 indicate that both level of roughage in the diet and
temperature influence feed intake. Because of lower lE at 27-32°C, the total
ME per unit of gain will be expected to rise when sheep are stressed by heat.
OCR for page 32
32
FARM ANIMALS AND THE ENVIRONMENT
TABLE 4 Effect of Alfalfa Hay-to-Concentrate Ratio on
Feed Intake of Sheep Under Cool and Hot Conditionsa
Hay : Concentrate
Ratio
Intake (g/day)
Cool (11-22°C) Hot (27-32°C)
25:75 1,000 820
50:50 1,180 1,032
75:25 1,050 1,016
75:25 + fat 879 868
Average 1,027 934
a Adapted from Bhattacharya and Uwayjan, 1975.
SWINE
The estimated relationship of feed intake to ambient temperature for pigs of
two weight ranges are shown in Figure 7. The associations of temperature
with feed intake were developed largely from studies under controlled tem-
perature conditions. Since commercial swine-rearing systems often include
some temperature modification, the laboratory data should parallel that ob-
served under farm systems. The temperature at which intake rises or declines
125
-
c:
a
to
so 100
111
Y
43: at
z ~
-.c 75
LL O
LL To
IL _
\
-
i` ~Is
Heavy Animals ~
\
-20 -10 0 10 20 30 40
TEMPERATURE ( C)
FIGURE 7. Effect of environmental temperature on feed intake of swine. (Solid lines are
40-70-kg animals; dashed lines are 70-120-kg animals) (adapted from Heitman and Hughes,
1949; Verstegen et al., 1978).
OCR for page 33
Feed Intake
33
is approximately the same for light and heavy pigs; however, heavy pigs
(above 70 kg) do appear to have a lower response threshold to heat stress
than smaller pigs (Figure 7~. In fact, the absolute feed intake of young pigs
(8 weeks of age) may be higher at 25°C (1.82 kg/day) than at 20°C (1.74 kg/
day). Growth rate of young pigs is moderately reduced under both cool
(10°C) and hot (30°C) conditions, however, the percent of the energy re-
tained may be higher at 30°C (43 percent) than at 10°C (34 percent) (Verste-
gen et al., 1978~. Experimental evidence to date clearly shows there is an
important interaction effect of size of pig and EAT.
POULTRY
Laying hens will acclimate to a fairly wide range of temperature conditions,
e.g., Davis et al. (1972) showed laying hens reared at 18°C required only
2-3 weeks to reach a new equilibrium of 160 kcal ME/kg 0.75/day after
change to a 35°C environment (Figure 8~. When the hens were shifted from
18 to 7°C, their ME intake was lowered for approximately 1 week due to be-
havioral adaptation before feed intake returned to a level of about 102 per-
cent of the amount consumed before the shift.
The estimated changes in feed intake for laying hens acclimated to the en-
vironmental temperature and fed a diet of 3.17 kcal ME/g DM iS shown in Fig-
ure 9. Below 5°C an increase in feed intake is required to provide for higher
maintenance requirements. Data are limited on intake for temperatures as
~ 200
US
o
-
A
-
UJ
A
z 1 00
\,,
7 C
- 35°C
0 1 2 3
WEEKS
4 5 6 7
FIGURE 8. ME intake of laying hens after being moved from an 18°C
environment to a 35 or 7°C environment (adapted from Davis et al.,
1972).
OCR for page 34
34
O 110
(~) on
A:
UJ
Y
~ ~ 90
Z UJ
_ y
LU ~
It Z 70
FARM ANIMALS AND THE ENVIRONMENT
130 ~
hi_
-
) _
1 1 1
-
50
0 5 10 15 20 25 30 35
TEMPERATURE ( C)
FIGURE 9. Estimated change in feed intake for laying hens. Based on data in Table 38.
low as 0°C. Similar to other species, level of intake at low temperatures is
erratic due to behavior changes to alleviate rapid heat loss; hence, the intake
curve is represented by a broken line below 5°C and represents an extrapola-
tion of needs for thermal equilibrium.
Under commercial production systems, where temperature inside the
house may range from 2~37°C, the feed intake of laying leghorns will de-
crease by 1.0 to 1.5 g per day per 1°C from 25 to 34°C but by 4.2 g per 1°C
from 32 to 36°C (Davis et al., 19731. Level of protein in the diet appears to
have an interaction effect on feed intake of laying hens under thermal stress
(McNaughton et al., 19781. For summer feeding in temperate areas and
throughout the year in hot climates, a crude protein of 25 percent or higher in
the ration is recommended for good efficiency, whereas less than 25 percent
cP is satisfactory at temperatures below 25°C for laying hens.
Representative terms from entire chapter:
dry matter
