Studies on the energy content of pigeon feeds I. Determination of digestibility and metabolizable energy content

Abstract

The digestibility coefficient and metabolizable energy (ME) content of the most important pigeon feeds (corn, wheat, barley, red and white millet, sorghum, canary seed, peas, lentils, sunflower, and hemp) were determined. The experiment was carried out using 10 adult male homing pigeons. All feeds were fed alone, in a whole-grain form, ad libitum. Drinking water and grit were offered to the birds on a continuous basis. Each feedstuff was fed to five pigeons in 1-wk cycles. There was no significant difference between the values determined in pigeons and those reported in the literature for chickens among the digestibilities of the CP of the various feeds. For pigeons, the digestibility of carbohydrates (N-free extracts, NFE) was lower (e.g., 62.37 vs 83.00% for barley and 63.45 vs 77.00% for peas), whereas the ether extract (EE) was higher (e.g., 75.58 vs 61.00% for barley and 82.59 vs 80.00% for peas) in pigeons compared with chickens. As a result, the AMEn values determined in pigeons did not differ significantly from those reported for chickens but tended to be slightly higher. For feeds of high-oil content, that difference may be somewhat larger. The correlation between the CP, EE, crude fiber (CF), and NFE contents of the feeds and the ME values determined in this experiment were calculated by multivariate linear regression. It was concluded that it was more accurate to determine and tabulate the ME contents of other potential pigeon feeds directly by experimental methods rather than using an equation.

Full text

Studies on the Energy Content of Pigeon Feeds I. Determination of
Digestibility and Metabolizable Energy Content
I. HULLAR,* I. MELEG,† S. FEKETE,*
,1
and R. ROMVARI†
*Department of Animal Breeding, Nutrition and Laboratory Animal Science, University of Veterinary Science,
H-1400 Budapest, P.O. Box 2, Hungary and †Faculty of Animal Science,
Pannon University of Agricultural Sciences, Kaposvar, Hungary
ABSTRACT The digestibility coefficient and metaboliz-
able energy (ME) content of the most important pigeon
feeds (corn, wheat, barley, red and white millet, sorghum,
canary seed, peas, lentils, sunflower, and hemp) were
determined. The experiment was carried out using 10
adult male homing pigeons. All feeds were fed alone, in
a whole-grain form, ad libitum. Drinking water and grit
were offered to the birds on a continuous basis. Each
feedstuff was fed to five pigeons in 1-wk cycles. There
was no significant difference between the values deter-
mined in pigeons and those reported in the literature for
chickens among the digestibilities of the CP of the various
feeds. For pigeons, the digestibility of carbohydrates (N-
free extracts, NFE) was lower (e.g., 62.37 vs 83.00% for
(Key words: pigeon, feed, digestibility, energy, prediction)
1999 Poultry Science 78:1757–1762
INTRODUCTION
Experiments necessary for determining the nutrient
requirements of pigeons are rendered difficult because
of several characteristic features of these birds (Waldie
et al., 1991): 1) Young pigeons continuously stay in the
nest and are dependent on their parents for feed intake;
2) Initially, the parents feed the squabs with a special
feed, so-called “crop milk”; and 3) Parents are strictly
monogamous, and the pair remain together throughout
their lives.
The scarcity of experimental data available on the nu-
trient requirements of pigeons is likely attributable to
the above factors. The greatest amount of available infor-
mation is related to protein requirements; however, the
reported values show rather wide variation. At the same
time, numerous indirect data exist on the breed-related
weight and weight gain (Pelzer, 1990a,b) as well as the
feed conversion ratio (Rizmayer, 1969) of young meat-
type pigeons. Total annual feed consumption per pair
Received for publication March 29, 1999.
Accepted for publication September 1, 1999.
1
To whom correspondence should be addressed: sfekete@iif.hu;
safekete@ns.univet.hu
1757
barley and 63.45 vs 77.00% for peas), whereas the ether
extract (EE) was higher (e.g., 75.58 vs 61.00% for barley
and 82.59 vs 80.00% for peas) in pigeons compared with
chickens. As a result, the AME
n
values determined in
pigeons did not differ significantly from those reported
for chickens but tended to be slightly higher. For feeds of
high-oil content, that difference may be somewhat larger.
The correlation between the CP, EE, crude fiber (CF), and
NFE contents of the feeds and the ME values determined
in this experiment were calculated by multivariate linear
regression. It was concluded that it was more accurate to
determine and tabulate the ME contents of other potential
pigeon feeds directly by experimental methods rather
than using an equation.
has been measured directly in large-scale trials, and
based upon the measured data, recommendations have
been formulated for the nutrient content of mixed feeds
(Morice, 1970; Levi, 1972, 1974; Klein, 1974; Orban, 1975;
Csontos, 1981; Bo
¨
ttcher et al., 1985).
Vandeputte-Poma and Van Grembergen (1967) and
Hegde (1972) published valuable data on the amino acid
composition of pigeon crop milk. From the digestive
physiological point of view, the observations reported
on the passage of feed through the crop are especially
interesting. For instance, 15 g of wheat leaves the crop
in 11 to 17 h, whereas the same quantity of barley takes
18 to 23 h (Kakuk, 1991). In that context, an interesting
comparison was made possible by the experiments of
Bokori (1968) on growing chickens, which revealed that
labeled corn was completely excreted from the crop by
the end of the fourth hour after feeding.
The digestive tract of pigeons in relation to body size
is shorter than that of fowl (7:1 vs 8:1; Kakuk, 1991),
presumably because of their flying ability, which re-
quires that the body be as light as possible. At the same
time, because of their lively temperament and high meta-
Abbreviation Key: CF = crude fiber; DC = digestibility coefficient;
EE = ether extract; NFE = N-free extract; OM = organic matter.

HULLAR ET AL.1758
bolic rate, pigeons require a larger quantity of feed in
proportion to their body weight. Because of the faster
intestinal passage resulting from this metabolism, the
efficiency of digestion is assumed to decrease. However,
only few data, determined by specific digestion experi-
ments, are available to support these concepts (Engel-
mann, 1963). An accurate knowledge of the nutrient re-
quirements is only one of the conditions necessary for
formulating pigeon diets that are nutritionally adequate.
The other basic precondition would be to know the nutri-
ent digestibility and ME content of individual feed ingre-
dients. The relevant tabulated values have been derived
from experiments on chickens and, because of lack of
more precise data, these values are being used in the
formulation of pigeon diets. Therefore, the objective of
the present experiment was to determine the apparent
digestibility coefficients (DC) and AME
n
contents of
grains regarded as the most important pigeon feeds.
Our aim was to provide basic data for more precise
formulation of mixed feeds and to determine whether
the tabulated values obtained for chickens could be used
in the formulation of pigeon diets.
MATERIALS AND METHODS
Experimental Design
The experiment was carried out in the animal facilities
of the Department of Animal Breeding, Nutrition and
Laboratory Animal Science, University of Veterinary Sci-
ence, Budapest, Hungary in January and February, using
10 adult (2- to 3-yr-old) male homing pigeons with an
average BW of 460 g. The birds were housed individually
in metabolic cages suitable for quantitative measure-
ment of the diet consumed, as well as the excreta pro-
duced. A room temperature of 15 to 18 C and a relative
humidity of 60 to 75% were maintained throughout the
experiment. The concentration of CO
2
was less than 0.2
vol %, whereas that of NH
3
was less than 0.002 vol %.
The test feeds included corn, wheat, barley, red millet,
white millet, sorghum, canary seed, peas, lentils, sun-
flower, and hemp. All feeds were consumed alone, in
grain form, ad libitum. Drinking water and grit were
offered to the birds on a continuous basis. All birds were
cared for according to the Canadian Council on Animal
Care guidelines (CCAC, 1993).
Sample Collection and Chemical Analysis
Each feedstuff was fed to five pigeons in 1-wk cycles.
The experimental phase consisted of two parts, the pre-
feeding period (3 d) and the main feeding phase (4 d).
During the main phase, the amount of feed consumed
was measured daily on an individual basis. Excreta were
collected from each bird twice each day and were stored
2
IKA-WERKE GmbH & Co. KG., D-79217 Staufen, Germany.
at −20 C until laboratory analysis. The 4-d excreta of one
bird constituted one sample.
The gross energy (GE) content of feed and excrement
samples was determined using an IKA C-400
2
-type adia-
batic calorimeter. Separation of the N content of excreta
into N of urinary and fecal origin was done by a chemical
method (Jakobsen et al., 1960). The DM, ash, CP (N ×
6.25), crude fiber (CF), and ether extract (EE) contents
of feed and excrement samples were determined ac-
cording to the AOAC (1975).
Calculations and Statistical Analysis
Correlation among the CP, EE, CF, and N-free extract
(NFE) contents of the feeds and the AME
n
values experi-
mentally determined by us were analyzed by multivari-
ate linear regression (SPSS for Windows 5.0.1., 1992).
Statistical evaluation of the DC and the ME values was
done by the two-tailed t-test by SPSS for Windows 5.0.1.
(1992) software.
This study was approved by the Animal Use and Care
Administrative Advisory Committee of the Hungarian
Scientific Chamber and complied with European Union
directives regarding the use of experimental animals
(CECAE, 1992).
RESULTS AND DISCUSSION
The chemical composition of the feeds and gross en-
ergy content were determined with a bomb calorimeter
and are presented in Table 1. The data indicate that, the
cereal grains, of the red-hulled variety of millet contains
a somewhat higher amount of protein and energy than
the white-hulled variety, although the difference was
not significant. Canary seed contains a higher level of
protein and more oil than millet. Peas and lentils are
important protein sources, are low in EE, and most of
their energy content comes from starch. Sunflower and
hemp are good protein sources and provide considerable
amounts of energy because of their oil content.
Table 2 shows the feed consumption values measured
during the 4-d experimental cycles. The apparent digest-
ibility and AME
n
values of the nutrients of the test feeds,
determined by a metabolic trial, are summarized in Table
3. Of all the feeds tested, corn had the highest dry and
organic matter (OM) digestibility, but other cereal grains
also had high digestibilities. In contrast, the digestibili-
ties of lentil and hemp were of medium level. Interest-
ingly, the digestibility of CP was excellent for all feeds,
and that of the EE was similarly good for all feeds, except
wheat and barley. At the same time, the digestibility of
NFE could be considered only moderately good. The
data seem to confirm the findings of Goodman and Grim-
inger (1969), who suggested that pigeons could more
efficiently utilize lipids than carbohydrates as energy
sources.
The possibility is limited for comparing the data ob-
tained in the present experiments with those of the litera-
ture, because very little relevant data have been pub-

PIGEON FEED DIGESTIBILITY AND METABOLIZABLE ENERGY VALUE 1759
TABLE 1. Chemical composition and gross energy content of the feedstuffs
Feedstuff
1
DM Ash OM CP CF EE NFE GE
(%) kcal/kg
Corn 89.89 1.32 88.57 10.10 1.95 3.70 72.82 4,167
Wheat 90.28 1.69 88.59 13.70 2.06 1.73 71.10 4,084
Barley 89.56 3.08 86.48 11.40 3.91 2.13 69.04 3,869
Millet (red) 90.18 2.98 87.20 12.40 6.79 4.13 63.88 4,379
Millet (white) 86.83 2.71 84.12 11.55 6.64 3.95 61.98 4,110
Sorghum 86.68 1.76 84.92 11.65 2.65 4.08 66.54 3,924
Canary seed 89.10 5.21 83.89 16.90 4.63 6.30 56.16 4,241
Peas 90.21 2.80 87.41 23.40 3.72 1.10 59.19 4,220
Lentils 89.16 2.80 86.36 26.15 2.90 1.20 56.11 4,067
Sunflower 95.25 3.55 91.70 17.77 13.46 44.38 16.16 6,391
Hemp seed 94.68 5.06 89.62 24.13 20.72 32.38 12.39 5,597
1
OM = organic matter; CF = crude fiber; EE = ether extract; NFE = nitrogen-free extract; and GE = gross
energy.
lished for pigeons. Table 4 presents the values obtained
by Engelmann (1963) in experiments comparing the di-
gestibility of the OM content of some grains fed to chick-
ens and to pigeons. In the present experiment, the OM
digestibility of wheat was found to be practically identi-
cal, that of barley higher, and those of peas and lentils
were lower than the respective values reported by Engel-
mann (1963).
The data reported in the literature for chickens offer
somewhat more opportunity for comparing our findings
in pigeons. This comparison is intriguing because, as
mentioned earlier, the length of the digestive tract rela-
tive to body size is shorter in pigeons (7:1) than in fowl
(8:1; Kakuk, 1991). The relative shortness of the pigeon’s
intestinal tract is, however, partially compensated for
by the well-developed network of intestinal villi cov-
ering the intestinal mucosa, as well as by the more acidic
character of all portions of the intestinal tract (crop, giz-
zard, intestines) compared with that of the fowl. In view
of the above theoretical considerations, it would be inter-
esting to know whether there are any differences be-
tween the two species in the digestibility and ME of the
same feeds.
Table 5 presents those feeds for which reference data
determined in chickens are available in the literature.
As shown in the table, the pigeon diet includes many
feeds that are seldom used in conventional poultry feed-
TABLE 2. Average feed consumption of pigeons in different stages
of the experiment (g)
Feed intake rank Mean
1
SD %
1. Peas 132.00 5.96 100.00
2. Millet (white) 106.68 18.31 80.82
3. Canary seed 106.10 21.78 80.38
4. Lentils 105.95 29.06 80.26
5. Hemp seed 101.90 18.45 77.20
6. Barley 92.40 9.57 70.00
7. Corn 90.62 17.89 68.65
8. Millet (red) 86.46 10.38 65.50
9. Sunflower 76.80 17.89 58.18
10. Wheat 69.62 15.96 52.74
11. Sorghum 64.30 26.78 48.71
1
Grams per 4 d; n = 5.
ing; thus, the literature contains no data for them. Com-
parison is rendered difficult because the values pub-
lished in tables represent the average of several experi-
ments and because the analyzed samples are not
identical. After this preliminary remark, it is shown that
corn, wheat, peas and sunflower are the feeds for which
the DC of CP measured in pigeons are the closest to
those found in chickens. The finding applies to the di-
gestibility of EE for peas and sunflower. With the excep-
tion of sunflower, the digestibility of NFE of all feeds
was lower in pigeons. From this result, lower energy
utilization can be expected. The comparison of the ME
values shows that the values contained in the European
Table (Janssen, 1989) tend to be lower than those of the
NRC (1994). The values obtained from pigeons are closer
to the figures of the cited European Table but are usually
slightly higher than the latter. This comparison seems
to contradict the statement concerning the digestibility
of the NFE. It is striking, however, that in pigeons the
DC of the EE of feeds are higher. This result suggests
that pigeons can probably utilize lipids more efficiently
than carbohydrates as an energy source. Although the
pigeon, like the horse and rat, does not have a gallblad-
der, the lack of that organ does not prevent the utilization
of fat contained in oilseeds, because bile production in
the liver can adapt to the changing demands in a versa-
tile manner.
The question arises whether an applicable equation
can be formulated from the experimental data for as-
sessing the ME content of the hitherto unanalyzed pi-
geon feeds. While investigating that possibility, the fol-
lowing correlations were found by multivariate linear
regression between the CP, EE, CF, and NFE content of
the feeds and the ME values experimentally determined
by us:
AME
n
= 7.494 × EE + 1.885 × CP − 0.310
× CF + 2.387 × NFE + 1268,
where AME
n
is expressed in kilocalories per kilogram,
and EE, CP, CF, and NFE are as grams per kilogram
of feed.

HULLAR ET AL.1760
TABLE 3. Digestibility and AME
n
content of the feeds analyzed (n = 5)
Dry Organic Crude Ether N-free
Feed matter matter protein extract extract AME
n
(%) (kcal/kg)
Corn 81.25 82.38 85.15 82.33 77.27 3,527
SD 2.83 2.31 1.80 7.39 2.88 114
Wheat 75.52 77.80 85.75 73.20 70.85 3,325
SD 2.62 1.24 1.50 3.71 1.43 29
Barley 71.25 71.84 86.30 75.58 62.37 2,955
SD 2.38 3.14 1.89 4.90 4.10 107
Millet (red) 67.35 73.83 84.16 90.44 65.43 3,530
SD 3.86 2.88 1.76 1.98 3.62 100
Millet (white) 70.86 75.18 85.35 90.69 68.21 3,284
SD 2.66 3.29 1.71 2.49 4.34 143
Sorghum 76.81 82.13 86.02 93.32 77.57 3,315
SD 4.42 1.62 1.55 0.42 2.05 48
Canary seed 69.32 74.53 85.75 94.10 68.57 3,508
SD 5.97 5.23 2.98 2.60 6.32 155
Peas 71.71 71.20 85.70 82.59 63.45 3,348
SD 2.97 3.14 1.41 5.97 4.18 98
Lentils 64.65 65.51 85.48 93.64 56.21 3,057
SD 1.32 4.16 1.71 1.93 5.31 117
Sunflower 69.28 68.98 85.97 98.10 57.56 5,301
SD 5.17 5.46 3.11 0.46 7.70 167
Hemp seed 58.58 63.95 86.86 98.44 51.62 4,308
SD 5.12 5.75 1.79 0.45 7.82 243
AME
n
= Apparent metabolizable energy corrected to zero nitrogen retention.
For the equation, r
2
= 0.95, the correlation was highly
significant (P < 0.001). These favorable values, however,
do not mean that no doubts arise regarding the validity
and applicability of the above equation. One of the prob-
lems is that, of the coefficients of the independent vari-
ables, only the ether extract has an acceptable signifi-
cance level (P < 0.05). In addition, the standard error is
rather high as compared with the coefficients (EE: 3.22,
CP: 3.77, CF: 5.06, and NFE: 3.75). Furthermore, based
upon the correlation calculated according to Snedecor
and Cochran (1967), there is a very close correlation
between the individual independent variables (e.g., NFE
− CF: r = 0.93; NFE − EE: r = 0.94). Because of the similarly
strong correlation for AME
n
and EE (r = 0.96), the ques-
tion arises as to how much that close correlation can be
attributed to the combined effect of the other variables.
By calculating the partial correlation coefficient, it be-
came clear that AME
n
and EE are closely correlated (r
= 0.69) even if the effects of the other variables are disre-
garded. Subsequently, we calculated the multivariate
linear regression by the stepwise method (Hochberg and
Tamhane, 1987). Only one factor, i.e., the EE, proved to
have a significant effect. Therefore, the answer to the
original question (whether an applicable equation can
be formulated from the experimental data for assessing
the ME content of the hitherto nonanalyzed pigeon
feeds) is no, at least on the basis of the available data.
A possible solution would be to expand the feed data-
base by results from further experiments. This solution
is, however, restricted by the limited number of different
feeds usually fed to pigeons. In addition, increasing the
number of samples in itself will not guarantee the relia-
bility of the equation. Ha
¨
rtel (1977) could not obtain
reliable results even after analyzing as many as 40 poul-
try feeds. According to his statement, the assessment of
ME on the basis of crude nutrient content is markedly
hindered by the fact that their digestibility may mark-
edly differ depending on the feeds in which they occur.
Excluding some “extreme” feeds, which would reduce
the accuracy of correlation, can increase the reliability
of the equation, which would set a limit to general appli-
cability. In view of all these considerations, a feasible
solution would be to increase the number of analyzed
feeds up to a rational limit and to tabulate the results
obtained, which could then be used for the formulation
of pigeon feeds without applying the assessment
equation.
In the context of energy requirements, several re-
searchers have studied which energy sources can be con-
sidered most favorable for pigeons. It is accepted that
TABLE 4. Comparison of some grain feeds for the digestibility of
organic matter in chickens and pigeons
Organic matter digestibility (%)
Feed Chicken
1
Pigeon
1
Pigeon
2
Wheat 81.1 78.1 77.8
Barley 72.8 64.1 71.8
Oats 73.2 61.9 . . .
Peas 80.0 77.9 71.2
Lentils 87.0 74.6 65.5
Broad beans 89.0 70.0 . . .
1
Engelmann (1963).
2
Present data.

PIGEON FEED DIGESTIBILITY AND METABOLIZABLE ENERGY VALUE 1761
TABLE 5. Comparison of the digestibility coefficients (DC) of feeds obtained in these experiments for
pigeons with reference values reported in the literature for chickens
1
AME
n
DC (%) (kcal/kg)
CP EE NFE
Feeds I II I II I II I II III
Corn 85.15 84.00 82.33 92.00 77.27 90.00 3,527 3,501 3,346
Barley 86.30 68.00 75.58 61.00 62.37 83.00 2,955 2,871 2,637
Sorghum 86.02 72.00 93.32 83.00 77.57 91.00 3,315 3,379 3,208
Peas 85.70 86.00 82.59 80.00 63.45 77.00 3,348 2,802 2,566
Sunflower 85.97 85.00 98.10 96.00 57.56 12.00 5,301 3,425 . . .
1
I = present data; II = Janssen (1989); III = NRC (1994); and AME
n
= apparent metabolizable energy corrected
to zero nitrogen retention.
fat is the main energy source for breast muscle function
during prolonged flight. According to George and Jyotti
(1955), in pigeons 77% of the energy necessary for muscle
function is derived from the oxidation of lipids. Pigeon’s
crop milk is also known to contain much fat. These re-
sults prompted researchers to study what nutrients (lip-
ids and carbohydrates) would be needed as an energy
source for enhancing the performance of racing pigeons.
Goodman and Griminger (1969) conducted five experi-
ments with racing homing pigeons to observe the effect
on performance exerted by the energy source. In each
experiment in which fat supplementation was used (the
fat content of the feed was raised from 3.4 to 8.4%, from
3.7 to 8.7%, and from 3.7 to 6.8%), the pigeons receiving
the fat-supplemented feed surpassed the control pigeons
in performance. Twice as many experimental pigeons as
controls could travel a distance of 200 miles or more.
From these results it was inferred that flying pigeons are
likely to utilize fat more efficiently than carbohydrates as
an energy source. Borghijs and De Wilde (1992) and
Janssen et al. (1998) also stated that carnitine supplemen-
tation of the feed had a favorable effect on racing pi-
geons; it helped maintain the oxidative processes and
prevent muscle damage during prolonged flight.
Summarizing our experimental findings, there was no
appreciable difference between pigeons and chickens in
the DC of the CP content of feeds. Although carbohy-
drates (NFE) have lower digestibility, EE has higher di-
gestibility in pigeons than in chickens. As a result, the
ME values determined in pigeons did not differ mark-
edly from those found in chickens but tended to be
slightly higher. This difference may be slightly more
pronounced for seeds rich in oil. The DC and ME values
as determined by this experiment may serve as reference
data for the manufacture of pigeon feeds.
ACKNOWLEDGMENTS
The authors wish to thank the Hungarian Academy of
Sciences (OTKA T 26606) and the Ministry of Education
(FKFP-0644/97) for financial support for this study, and
the Emese Andrasofszky for assistance in lab analyses.
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