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Daily Energy Intake of Broiler Chickens is Altered by Proximate
Nutrient Content and Form of the Diet
J. D. Latshaw
1
Department of Animal Sciences, The Ohio State University, Columbus 43210
ABSTRACT An experiment was designed to test the
ability of broiler chickens to equalize daily energy intake
when proximate components of the diet were changed.
A factorial arrangement was used to test effects of protein,
fat, and fiber content in the diet. The simplest diet con-
tained only corn and soybean meal to provide energy
and protein. Protein contents were calculated to be 16.4,
18.2, and 20.0%, with added protein from a combination
of corn gluten meal, fish meal, and peanut meal. Hy-
drolyzed fat was added at 0, 2.5, 5.0, and 7.5% of the
diets. A combination of alfalfa meal, oats, and wheat
middlings was used to increase the fiber of the corn soy
diet by approximately 2 and 4%. The 36 combinations
were fed as mash. In addition, 8 of the diets were fed as
pellets. All diets were fed for 12 d from the time broilers
reached approximately 1.2 kg. A total excreta collection
Key words: energy balance, fat, feed intake regulation, fiber, protein
2008 Poultry Science 87:89–95
doi:10.3382/ps.2007-00173
INTRODUCTION
There is continuing interest in explaining the regulation
of feed intake. Recent emphasis has linked the actions of
hormones produced by organs in the digestive system to
responses in the brain, mostly areas in the hypothalamus
and brain stem. Ghrelin is a hormone that is most preva-
lent in the stomach (Kojima et al., 1999), and in the brain is
concentrated in the arcuate nucleus of the hypothalamus.
High concentrations of ghrelin stimulate hunger and food
intake. When feed reaches the stomach and small intes-
tine, ghrelin release decreases. The overall effect of ghrelin
is to increase weight gain by increasing fat content of the
body (Tschop et al., 2000; Toshinai et al., 2006).
Several hormones act to decrease feed intake. The first
to be identified was cholecystokinin, which slows gastric
emptying but promotes bile secretion and pancreatic en-
zyme secretion (Gibbs et al., 1973; Kissileff et al., 1981).
Another hormone with similar effects is oxyntomodulin
©2008 Poultry Science Association Inc.
Received April 27, 2007.
Accepted September 13, 2007.
1
Corresponding author: Latshaw.1@osu.edu
89
was used to determine ME, and carcass analysis provided
fat and energy content. When fed mash, only sex had a
significant effect on grams of feed eaten per day. Sex and
dietary fat content affected gain per day. Sex, fat, and
fiber altered the kcal of ME eaten per day. Broilers fed
5% added fat ate approximately 10% more energy per
day than those fed no added fat, and broilers fed 4%
added fiber ate approximately 20% less ME than those
fed no added fiber. A comparison of results from mash
and pellets showed that only sex and form affected gain
per day, feed per day, and kilocalories of ME eaten per
day. For the mash and pellets, protein, fat, fiber, and
several interactions affected the ME per gram; however,
the ME per gram was similar for pellets and mash. The
results suggest that the diet composition and form have
a significant effect on the energy intake of broiler chickens.
(Dakin et al., 2001; Cohen et al., 2003). A hormone with
related effects is glucagon-like peptide 1, which inhibits
gastric emptying and gastric secretion (Turton et al., 1996;
Tang-Christensen et al., 2001).
The hormones named above have relatively short-term
effects and may affect the length of a meal. In some cases,
administration of the hormone decreased the length of the
meal, but a consequence was shorter intervals between
meals. For longer term energy balance, leptin has been
suggested. Leptin is produced mostly by white adipose
tissue, so higher concentrations are present in blood when
an animal has more body fat (Zhang et al., 1994; Morton
et al., 2005). The combination of leptin and insulin has
been proposed to be important in long-term regulation
of body fat (Schwartz et al., 2000), possibly through aden-
osine monophosphate kinase (Minokoshi et al., 2004). If
fat stores are high, increased secretion of these hormones
will be sensed in regions of the hypothalamus and con-
verted to signals that will decrease feed intake. If fat stores
are depleted, decreased concentrations of these hormones
will result in more feed intake to replace body fat.
Much of the information about leptin has come from
research with genetically obese rodents. Providing leptin
for animals that cannot synthesize leptin or its receptor
LATSHAW90
Table 1. Composition (%) of representative diets
Treatment
Ingredient 1 9 13 19 21 25 32
Corn 75.37 47.78 70.22 65.96 43.44 67.27 50.69
Soybean meal 20.58 16.81 23.23 22.98 18.62 23.29 22.00
Protein mix
1
0 0 3.25 3.25 3.25 6.50 6.50
Fat 0 4.50 0 4.50 4.50 0 4.50
Fiber mix
2
0 27.40 0 0 27.40 0 13.70
Dicalcium phosphate 1.36 1.23 1.18 1.19 1.05 1.01 0.95
Limestone 1.36 0.95 1.32 1.31 0.90 1.28 1.06
Salt 0.35 0.35 0.35 0.35 0.35 0.35 0.35
Vitamin and TM
3
0.20 0.20 0.20 0.20 0.20 0.20 0.20
Arginine 0.10 0.07 00000
Isoleucine 0.08 0.07 00000
Lysine HCl 0.24 0.25 0.10 0.10 0.11 0 0
DL
-Methionine 0.16 0.19 0.09 0.10 0.11 0.05 0.05
Threonine 0.14 0.15 0.06 0.06 0.07 0 0
Valine 0.06 0.05 00000
Calculated analysis
AME
n
(kcal/g) 3.06 2.99 3.01 3.25 2.97 2.91 3.09
1
The protein mix was 38.30% peanut meal, 30.85% menhaden fish meal, and 30.85% corn gluten meal.
2
The fiber mix was 20% alfalfa meal, 40% oats, and 40% wheat middlings.
3
The vitamin and trace mineral (TM) mix provided the following per kilogram of diet: retinyl palmitate, 6,000
IU; cholecalciferol, 1,000 ICU;
DL
-α-tocopherol acetate, 10 IU; menadione sodium bisulfite, 1 mg; thiamin, 1.8
mg; riboflavin, 3.6 mg; niacin, 25, 0 mg; pantothenic acid, 10.0 mg; pyridoxine, 3.5 mg; folacin, 0.5 mg; biotin,
0.15 mg; choline, 500 mg; ethoxyquin, 50 mg; copper, 8 mg; iron, 80 mg; manganese, 60 mg; selenium, 0.1 mg;
and zinc, 40 mg.
causes dramatic changes in energy balance. Funding for
such research is supported because of the problem with
obesity in humans (World Health Organization, 1998; Og-
den et al., 2006), most of whom are not genetically obese.
There is evidence that diet composition is a contributor
to excessive caloric intake. Some of the effect may relate
to palatability (Rogers and Blundell, 1984; Weinsier et
al., 1998). They described good palatability in terms of
increased number of calories consumed, increased meal
size, increased meal frequency, or a combination of these.
When rats were offered chow free choice or chow, bread,
and chocolate in a cafeteria style, those offered a choice
of foods ate more energy each day. They also ate little
chow and ate the more palatable feed. Energy density
was also examined as a variable to alter caloric intake
(Bell et al., 1998). Digestible energy per gram was altered
by an exchange between water and fat. Daily energy in-
take was significantly higher when women consumed the
diet with higher digestible energy content.
What has emerged is a difference in opinion about an
animal’s ability to regulate energy intake. One opinion is
that an animal has the ability to count ME calorie intake
and will adjust feed intake to accomplish this. This is
proposed to occur through hormonal regulation. A differ-
ent opinion is that an animal does not count ME calorie
intake accurately, eating more or less energy based on
dietary variables. Most poultry nutritionists favor the first
opinion (Leeson and Summers, 2001); however, NRC
(1994) was noncommittal. It cited some research that indi-
cated good regulation of caloric intake and some that
indicated deviation from accurate regulation. The pur-
pose of this research was to test the ability of broiler
chickens to equalize daily ME intake. Dietary variables
were protein, fat, and fiber, with an additional compari-
son of mash and pellets.
MATERIALS AND METHODS
Diets
Thirty-six different diets were prepared by using vari-
ous ingredients to alter the content of protein, fat, and
fiber. The diets were a factorial of 3 protein levels, 4 fat
levels, and 3 fiber levels. An initial diet was formulated
to provide approximately 16.4% protein using corn and
soybean meal as protein and energy sources (Table 1,
treatment 1). To meet amino acid requirements for broil-
ers from 3 to 6 wk (NRC, 1994), several amino acids were
supplemented. A protein mix of 38.30% peanut meal,
30.85% menhaden fish meal, and 30.85% corn gluten meal
was added at 3.25% of the diet to increase protein content
approximately 1.8% of the diet. For these diets, the protein
content of the final diet was calculated to be 18.2% (16.4%
+ 1.8%). The proportion of the diet that was corn and
soybean meal was reduced by 3.25% and rebalanced to
provide 16.4% protein, including supplemental amino
acids. Adding 6.5% of the protein mix increased dietary
protein approximately 3.6%.
Four fat levels were included in the diets. Hydrolyzed
animal and vegetable fat was added at 0, 2.5, 5.0, or 7.5%.
For each increasing fat level, corn and soybean meal were
reduced by the same percentage. Corn and soybean meal
were rebalanced to maintain protein content. Three fiber
concentrations were also included. To increase fiber, a
mix of 20% alfalfa meal, 40% oats, and 40% wheat mid-
dlings was used. The mix was added at 0, 13.7, or 27.4%
FAILURE TO REGULATE DAILY ENERGY INTAKE 91
Table 2. Means by treatment: analyzed protein, fat, fiber, and ME contents of the diets; daily feed, gain, and
ME intake; and fat and energy content of the carcass
Feed Carcass
Protein, Fat, Fiber, ME, Density, Feed, Gain, ME, Fat, Energy,
Treatment Form
1
% % % kcal/g g/cc g/d g/d kcal/d % kcal/g
1 M 16.63 2.26 6.02 2.750 0.689 152.6 63.67 420 9.71 1.982
2 M 16.84 2.08 6.57 2.744 0.644 146.0 56.90 401 11.02 2.043
3 M 16.88 4.01 9.46 2.620 0.587 150.4 56.17 394 11.13 2.009
4 M 16.48 4.67 5.57 3.095 0.663 155.1 71.47 480 12.82 2.157
5 M 16.51 5.05 7.34 2.999 0.597 153.1 68.70 459 13.20 2.150
6 M 16.64 5.13 9.30 2.658 0.544 153.7 65.12 409 11.89 2.011
7 M 16.65 6.51 4.88 3.086 0.677 153.1 70.69 472 14.12 2.323
8 M 16.89 6.60 7.37 2.962 0.624 151.1 61.35 448 10.82 1.990
9 M 17.06 7.73 9.81 2.866 0.539 147.0 60.50 421 13.23 2.136
10 M 16.88 8.39 5.82 3.204 0.677 154.5 76.61 495 13.66 2.295
11 M 17.02 10.28 7.15 2.965 0.615 167.3 74.98 496 13.90 2.238
12 M 16.91 9.57 9.45 2.776 0.535 164.1 72.15 456 12.52 2.179
13 M 18.36 3.39 6.50 2.889 0.749 142.0 61.70 410 11.49 2.062
113 P 18.46 2.29 4.54 2.826 0.735 167.6 80.03 474 12.87 2.237
14 M 19.08 2.72 7.18 2.616 0.636 150.0 59.64 392 11.02 2.079
15 M 18.59 2.70 9.54 2.607 0.636 142.3 53.13 371 10.66 2.012
115 P 18.73 2.51 8.13 2.539 0.696 196.3 78.66 498 13.24 2.224
16 M 18.42 4.60 5.71 2.926 0.696 153.1 72.79 448 13.64 2.159
17 M 18.45 4.58 8.38 2.844 0.615 161.4 69.41 459 11.58 2.099
18 M 18.54 4.64 9.46 2.683 0.544 137.1 52.44 368 8.42 1.850
19 M 18.55 7.06 5.40 2.968 0.774 161.6 69.41 480 12.33 2.142
119 P 18.47 5.62 4.64 2.965 0.735 168.6 78.32 500 13.69 2.278
20 M 18.65 6.52 7.52 2.924 0.620 147.4 67.10 431 12.95 2.128
21 M 18.47 7.70 10.77 2.593 0.630 150.7 58.87 391 12.66 2.188
121 P 18.57 6.34 8.84 2.539 0.644 181.8 82.35 462 13.17 2.105
22 M 18.72 8.67 5.61 3.129 0.688 168.9 83.03 528 13.49 2.148
23 M 18.41 9.30 7.58 2.990 0.604 134.6 60.33 402 12.47 2.141
24 M 18.43 9.62 10.67 2.737 0.558 155.4 62.55 425 13.33 2.142
25 M 20.19 2.63 5.70 2.716 0.760 154.6 65.72 420 12.82 2.138
125 P 20.28 2.64 5.95 2.899 0.741 179.9 83.03 522 14.11 2.281
26 M 20.37 2.35 7.53 2.591 0.644 151.4 60.50 392 12.05 1.970
27 M 20.31 2.73 9.57 2.581 0.650 144.6 57.58 373 11.52 1.945
127 P 20.22 2.14 8.17 2.567 0.677 189.6 78.66 479 11.31 2.047
28 M 20.26 4.51 6.69 2.982 0.692 161.0 73.69 480 12.62 2.209
29 M 20.47 4.29 8.26 2.949 0.611 154.0 66.50 454 12.21 2.157
30 M 20.28 4.53 9.09 2.891 0.544 147.4 60.58 426 12.04 2.035
31 M 20.25 6.18 6.20 3.046 0.774 144.2 71.38 439 12.96 2.218
131 P 20.37 5.71 5.17 3.177 0.702 165.3 82.35 525 13.73 2.168
32 M 20.39 8.00 7.70 3.001 0.624 147.7 72.32 443 12.50 2.244
33 M 20.21 7.74 10.28 2.775 0.617 145.1 62.04 403 12.40 2.111
133 P 20.44 6.20 9.61 2.770 0.655 172.0 65.41 476 12.19 2.088
34 M 20.38 8.95 6.46 3.194 0.677 149.6 76.52 478 14.85 2.356
35 M 20.32 10.39 9.26 3.007 0.607 139.0 69.13 418 13.36 2.134
36 M 20.47 8.75 9.98 2.849 0.544 130.9 56.64 373 12.85 2.166
1
Form: M = mash; P = pellets.
of the diet, each addition raising the fiber content approxi-
mately 2% of the diet. When 13.7% of the mix was added,
protein in the fiber mix was subtracted from the protein
content of the diet when no fiber mix was added. Corn
and soybean meal were reduced by 13.7% and rebalanced
so that the protein content of the diet was equal to that
when no fiber mix was added. The ME concentrations of
the diets increased when fat was added and decreased
when fiber was added (Table 2).
All of the diets were fed as mash. In addition, 8 of the
diets were fed as pellets. Diets that were fed as pellets
are listed as P under form in Table 2.
Experimental Design
Hubbard broilers were used for the experiment, which
consisted of 3 trials. In trial 1, only males were used. They
were fed a standard broiler starter in a floor pen until
the heaviest reached a weight of approximately 1,200 g.
Feed and water were removed at 2200 h. Beginning at
0800 h the following day, all birds were weighed individ-
ually. Those with the highest and lowest weights were
removed, keeping 50 of those with intermediate weights.
Forty-four were randomly selected and housed in indi-
vidual cages in a room maintained at 25°C. The other 6
were killed by cervical dislocation and frozen. Each
broiler was fed 1 of the 44 feeds for 12 d. Starting on d
7, one-third of the broilers were used for a 2-d digestion
trial. Total collection of excreta was done using plastic
sheeting suspended under the cages. One-third of the
broilers were started on d 8, and the remainder were
started on d 9. Samples were dried in a different room
that was heated to 27°C and had fans to circulate the air.
Dried samples were weighed and frozen.
LATSHAW92
Table 3. Treatment means, SEM, and statistical analysis of the results from all of the mash treatments
Treatment Feed, g/d Gain, g/d ME, kcal/d ME, kcal/g
Protein (%)
16.78 149.0 ± 3.5 64.3 ± 2.0 425.2 ± 9.5 2.860 ± 0.026
18.56 147.0 ± 2.6 63.0 ± 1.5 418.8 ± 7.2 2.839 ± 0.019
20.41 144.8 ± 2.6 63.4 ± 1.5 420.4 ± 7.1 2.899 ± 0.019
Fat (%)
2.76 144.1 ± 4.9 57.5 ± 2.8 395.7 ± 13.3 2.730 ± 0.036
4.67 148.1 ± 4.1 64.3 ± 2.4 421.7 ± 11.3 2.850 ± 0.031
7.12 147.2 ± 3.5 65.5 ± 2.0 434.7 ± 9.6 2.947 ± 0.026
9.32 148.4 ± 4.2 67.5 ± 2.4 433.7 ± 11.4 2.933 ± 0.031
Fiber (%)
5.88 148.9 ± 10.3 67.5 ± 6.0 470.6 ± 28.3 3.126 ± 0.076
7.65 146.8 ± 3.1 62.9 ± 1.8 417.3 ± 8.5 2.853 ± 0.023
9.78 145.2 ± 8.2 60.3 ± 4.8 376.4 ± 22.5 2.622 ± 0.061
Sex
Male 157.8 ± 1.8 68.7 ± 1.0 453.0 ± 4.8 2.867
± 0.013
Female 136.1 ± 2.8 58.4 ± 1.6 389.9 ± 7.8 2.866 ± 0.021
Probability of significance
1
Sex <0.01 <0.01 <0.01
Fat L 0.01 <0.01 <0.01
Fiber L <0.01 <0.01
Protein Q 0.04
Protein × fiber 0.03
Fat × fiber 0.01
Protein × fat × sex 0.04
Protein × fiber × sex 0.01
1
L = linear; Q = quadratic.
The broilers were fed for 12 d. At 2200 h of d 11, feed
and water were removed. Beginning at 0800 h of d 12,
each broiler was weighed, killed by cervical dislocation,
and frozen.
Trial 2 was begun 4 wk after trial 1. It was identical
except that half males and half females were used.
Twenty-six males and 26 females of intermediate weight
were kept for the trial. Four males and 4 females were
killed by cervical dislocation and frozen, and the re-
maining broilers were randomly distributed to cages.
Trial 3 was begun 4 wk after trial 2 and was almost
identical to trial 2. The only difference was that treatments
that had a male in trial 2 were assigned a female in trial
3, and vice versa. As a result, 2 males and 1 female were
fed each diet during the experiment.
Analyses
The density of each feed was determined. A pan that
held approximately 5 L was placed on a level balance.
The pan was almost filled with water. Then water was
added slowly until the pan began to overflow, at which
point the weight was recorded. The grams of water were
used as the volume, in cubic centimeters, of the pan. Each
feed was then added to the pan to overflowing, the excess
was scraped off, and the weight was recorded.
Protein, fat, and fiber concentrations of each diet were
determined. When the feeds were poured into a container
for each pen of chicks, a sample of approximately 200 g
was removed and saved before weighing the container.
Each sample was used to determine nutrient content
(AOAC, 2000): protein, Official Method 990.03; fat, Offi-
cial Method 963.15; and fiber, Official Method 973.18.
Energy content was determined with an adiabatic calo-
rimeter (Parr Instruments, Moline, IL). Excreta samples
were also used for energy determination.
Samples were prepared from carcasses. Each carcass
was thawed until it still retained some firmness. It was
then cut into pieces small enough to fit into a meat grinder
that had a plate with 1.27-cm holes. Each was reground
through a plate with 0.64-cm holes and then homogenized
with a food chopper. Several small samples were added
to an aluminum pan to provide a total sample of about
200 g. The sample was weighed, dried at 95°C for 2 d,
and reweighed. Each sample was reground using a coffee
grinder. Portions were used to determine fat content
(AOAC, 2000) and energy content.
Data were statistically analyzed using the GLM of SAS
(1996). The design was a randomized complete block,
with 3 time periods as blocks. Treatments were arranged
in a 3-way factorial design of fat, fiber, and protein. Effects
of sex and diet form were also determined. Results were
analyzed for interactions, and then main effects were de-
termined. Orthogonal comparisons of linear, quadratic,
and cubic responses were computed. Multiple linear re-
gression was used to develop several models.
RESULTS
The analyzed protein, fat, and fiber contents of the diets
are in Table 2. Protein percentage ranged from 16.48 to
20.47 and was close to calculated values. Fat percentage
ranged from 2.08 to 10.39%, and fiber ranged from 5.57
to 10.77%.
Differences in daily feed consumption of mash diets
were due to sex (Tables 2 and 3). Percentages of dietary
protein, fat, and fiber had no effect, and no interactions
were detected. Sex also affected daily gain (Tables 2 and
FAILURE TO REGULATE DAILY ENERGY INTAKE 93
Table 4. Treatment means, SEM, and statistical analysis of results from the 8 pellet treatments and the correspond-
ing mash treatments
Treatment Feed, g/d Gain, g/d ME, kcal/d ME, kcal/g
Protein (%)
18.56 156.9 ± 2.5 68.1 ± 1.6 422.6 ± 7.1 2.704 ± 0.019
20.28 157.5 ± 2.5 71.0 ± 1.6 439.7 ± 7.6 2.800 ± 0.019
Fat (%)
2.70 160.1 ± 2.9 68.2 ± 1.8 423.1 ± 8.3 2.654 ± 0.022
6.57 154.3 ± 2.9 71.0 ± 1.8 439.3 ± 8.3 2.851 ± 0.022
Fiber (%)
5.51 158.2 ± 11.2 72.4 ± 7.1 457.1 ± 32.0 2.904 ± 0.086
9.36 156.2 ± 11.2 66.8 ± 7.1 405.2 ± 32.0 2.600 ± 0.086
Sex
Male 171.3 ± 2.0 77.6 ± 1.3 472.3 ± 8.9 2.768 ± 0.016
Female 143.1 ± 2.9 61.5 ± 1.8 390.1 ± 8.3 2.736 ± 0.022
Form
Mash 144.0 ± 2.5 61.1 ± 1.6 398.6 ± 7.1 2.767 ± 0.019
Pellet 170.4 ± 2.5 78.1 ± 1.6 463.8 ± 7.1 2.737 ± 0.019
Probability of significance
Form <0.01 <0.01
<0.01
Sex <0.01 <0.01 <0.01
Fat × pellet 0.03
Protein <0.01
Fat <0.01
Protein × fat <0.01
Fiber × sex 0.02
Protein × sex × pellet 0.02
3), as did fat content of the diet. Again, no interactions
were found. The effect of increasing fat was a linear in-
crease in daily gain. Sex had no effect on the ME (kcal/
g) of the diet, but the fractions of the proximate analysis
did (Tables 2 and 3). There was a linear increase in ME
from adding fat and a linear decrease from adding fiber.
Increasing protein resulted in a quadratic response in ME.
Protein, fat, fiber content, and sex were all involved in
interactions affecting 2 or 3 of the variables. Sex, dietary
fat, and dietary fiber affected the kilocalories of ME eaten
per day (Tables 2 and 3) with no interactions detected.
Increasing fat caused a linear increase in daily ME con-
sumed, whereas increasing fiber caused a linear decrease
in daily ME consumed.
A comparison of results from the 8 diets that were fed
as pellets or mash is in Table 4. Daily feed consumption
was not affected by protein, fat, or fiber, but was affected
by sex and form. Broilers ate more grams of pellets each
day than mash. Gain per day was affected in the same
way as feed intake. The ME (kcal/g) was not affected by
sex or form. Increasing dietary protein and fat increased
the ME per gram of feed. Increasing fiber did not affect
ME but only because the variability of the samples was
several times as large as for other factors examined. Inter-
actions were found that involved all of the experimental
factors. The only factors that affected daily energy intake
(kcal of ME per d) were sex and form.
Coefficients to predict the ME of a diet based on protein,
fat, and fiber content are listed in Table 5. For mash, there
was a large coefficient for the intercept and relatively
large coefficients for fat and fiber content. The coefficients
for the quadratic effect of fat and the interaction of protein
and fiber were also included to adjust the ME in mash.
For pellets, the coefficient for the intercept was less than
half of that for the mash intercept. The coefficient for fiber
indicates a fairly small change in energy due to fiber,
but fat and protein coefficients show they substantially
increase the ME of the diet. No interactions were signifi-
cant when predicting the ME of pellets.
The effect of experimental variables on density of the
diet was examined (Table 6). Changes in protein and fat
did not affect density, but fiber did. In addition to the
effect of fiber, there was an interaction between form and
fiber. Separation of the effects showed that mash was
more dense than pellets when fiber was low, as found in
a corn-soy diet; however, when diets contained additional
fiber, mash was less dense than pellets.
Experimental treatments that increased the daily intake
of ME also increased the body fat of broilers (Table 7).
Each increase of 100 kcal of ME per d increased body fat
by 1.2%.
DISCUSSION
Broilers used in this experiment were not able to equal-
ize daily ME intake when the diet composition and diet
form were variables. A possible explanation for difference
Table 5. Regression equations for apparent ME (kcal/g)
Parameter Coefficient SE P > (t)
Mash treatments, 108 observations
Intercept 2.883 0.086 <0.001
Fat (%) 0.127 0.024 <0.001
Fiber (%) −0.100 0.021 <0.001
Fat × fat −0.007 0.002 0.001
Fiber × protein 0.002 0.001 0.048
Pellet treatments, 24 observations
Intercept 1.271 0.619 0.053
Fiber (%) −0.014 0.016 <0.001
Fat (%) 0.072 0.018 0.001
Protein (%) 0.097 0.012 0.007
LATSHAW94
Table 6. Treatment effects on density
1
Treatment Density SE P > (t)
Protein (%) g/c
3
18.56 0.699
20.28 0.697 0.94
Fat (%)
2.70 0.705 0.65
6.57 0.691
Fiber (%)
5.51 0.746 0.024 <0.001
9.36 0.650 0.026
ANOVA
Treatment P > (t)
Fiber <0.001
Form 0.99
Fiber × form 0.001
Treatment means
Fiber, 5.51; Mash 0.764 0.012
Fiber, 5.51; Pellet 0.728 0.018
Fiber, 9.36; Mash 0.632 0.014
Fiber, 9.36; Pellet 0.668 0.023
1
n = 16 observations.
in results from the present research and from some other
research related to energy regulation lies in experimental
design. The present research examined a larger range of
dietary energy than is usually reported. In Table 2, the
diet with the lowest ME, 2.54 kcal/g, contained 80% of
the energy concentration in the diet with the highest ME.
It is relatively difficult to develop diets with a large range
of ME. For example, adding 0.5% methionine to a corn-
soy diet in place of corn more than doubles the diet methi-
onine; however, adding 0.5% fat in place of corn increases
dietary energy by less than 1%.
As a result, energy studies may need a greater number
of observations so that significant differences can be de-
tected. Comparing diets that are different by 100 or 200
kcal of ME/kg may give daily energy intakes that are
statistically similar, but extending the range of diet energy
might show that energy content has a significant effect
on daily energy intake. Increasing levels of dietary fiber
caused large decreases in the daily ME intake (Table 3),
even though the fiber content had no effect on the amount
of feed eaten each day. A similar but more pronounced
effect is present in dairy cattle (Conrad, 1966; NRC, 1988).
Forages may contain 40% or more fiber. To increase en-
ergy intake needed for higher milk production, high fiber
ingredients must be replaced by low fiber ingredients.
Higher dry matter intake and, therefore, energy intake
result when dietary fiber is decreased, due to direct or
indirect effects of fiber (Allen, 2000).
Table 7. Body fat (%) as affected by ME intake
Parameter Estimate SE P < (t)
Intercept 2.535 1.462 0.085
Sex
1
3.398 0.343 <0.001
ME (kcal/d) 0.012 0.003 <0.001
1
Sex: male = 1; female = 2.
In contrast to results with fiber, increasing levels of
dietary fat increased the daily ME intake, although the
effect was not as large as for fiber and appeared to reach
a maximum at a level of approximately 5% added fat.
These results are similar to those found in humans (Lis-
sner and Heitmann, 1995) and rats (Rogers and Blundell,
1984). Dietary protein, within a range that was needed
to meet amino acid requirements, did not affect ME intake
per day. This is in contrast to what was reported from
other research (Stubbs, 1999).
Broilers that were fed pellets had a higher ME intake
per day than those fed mash. As was reported previously
(Sibbald, 1977), there was no difference in the ME/gram
of mash and pellets. If the hormonal regulation of energy
balance that is proposed for mammals (Schwartz et al.,
2000) is also present in broilers, it is not very effective.
Broilers that ate more energy per day (Table 7) had more
body fat, which should have resulted in more leptin pro-
duction and less energy consumption. The results of the
present experiment suggest that hormonal regulation of
feed intake should be considered only a coarse adjust-
ment, with other factors determining the amount of daily
energy actually consumed. Palatability may be an im-
portant component of fine tuning energy intake, espe-
cially when an animal has no alternative to the complete
diet that is provided.
When diets were mixed, it was obvious that adding fat
decreased the dustiness of the diets, and adding fiber
increased the dustiness of the diets. If dustiness is a com-
ponent of palatability, the results from the present experi-
ment indicate that broilers prefer diets that are not dusty.
Behavior of the broilers also indicated that the higher
fiber diets were more difficult to swallow: chickens
needed several attempts to swallow a mouthful of the
higher fiber diets. The results of the present experiment
also indicate that pellets are a more important consider-
ation in palatability than fat or fiber. When mash was
fed, both fat and fiber content of the diet affected the
energy intake per day (Table 3), but when the same diets
were fed as pellets, neither fat nor fiber content caused
a significant effect (Table 4).
The effect of pellets cannot be attributed to density of
the diet (Table 6), because pellets of a high fiber diet were
slightly more dense than the corresponding mash, but
pellets of the low fiber diet were slightly less dense than
the corresponding mash. In an experiment with White
Leghorn hens, the effect of energy density was separated
from the effect of bulk density (Cherry et al., 1983) by
diluting a diet with 20% wood fiber or 20% sand. Hens
fed the sand diet adjusted feed intake so that caloric intake
and rate of egg production were higher than for those
fed the wood fiber diet. Bulk density results from the
present experiment are different from previous research
(Skoch et al., 1983). In that research, bulk density was
0.50 for the corn-soy diet in mash form and 0.68 when
pellets were formed using steam. No explanation for the
different observations in the 2 experiments is available.
Bulk density is probably affected by air spaces among
particles of the ingredients. For the low fiber diets, air
FAILURE TO REGULATE DAILY ENERGY INTAKE 95
spaces among the pellets are probably larger than spaces
between ingredient particles. For the high fiber diets, the
reverse is probably true.
Results of the present experiment indicate that chang-
ing the proportions of the proximate analysis and the
form of the feed significantly affect the amount of ME
eaten by broiler chickens each day. This knowledge may
be important for increasing energy intake, especially
when the available ingredients have higher amounts of
fiber. When diets have relatively low amounts of fiber, it
may be of economic importance to determine if responses
due to adding fat and forming pellets cancel each other.
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