Download Protein quality of linseed for growing broiler chicks

Animal Feed Science and Technology
84 (2000) 155±166
Protein quality of linseed for growing broiler chicks
J. TrevinÄo*, M.L. RodrõÂguez, L.T. Ortiz, A. ReboleÂ, C. Alzueta
Departamento de ProduccioÂn Animal, Facultad de Veterinaria, Universidad Complutense,
Ciudad Universitaria, 28040 Madrid, Spain
Received 19 July 1999; received in revised form 19 October 1999; accepted 2 March 2000
Abstract
The protein quality of linseed was assessed and compared to that of soybean meal (SBM) in two
experiments using growing broiler chicks. In the ®rst experiment, the protein ef®ciency ratio (PER)
and net protein ratio (NPR) were calculated for diets (90 g crude protein kgÿ1) containing the
following sources of protein: SBM and SBM diet modi®ed to contain 10, 30 and 100% of the total
protein from linseed. There was a signi®cant (P<0.001) relationship between performance data or
PER and NPR values and inclusion rate of linseed in the diet. When fed as the sole source of
protein, linseed caused a drastic reduction in weight gain (97.6 versus 6.9 g) and PER (3.38 versus
0.40) and NPR (4.29 versus 1.96) values compared to those for SBM. In the second experiment, apparent
and true total tract retentions (ATTR and TTTR) for nitrogen and amino acids were determined for diets
(150 g crude protein kgÿ1) containing SBM as reference protein or SBM protein replaced 10 and 30%
by linseed protein. The ATTR values were 15.3 and 24.8% lower for nitrogen and 4.6 and 15.5% lower
for total amino acids for diets containing linseed to compared to SBM diet. The response of individual
amino acids to inclusion level of linseed was linear (P<0.001). The TTTR values followed a similar
trend than that found for apparent retention. In conclusion, utilization of linseed protein by broiler chicks
was worse than that from SBM and it attributable in all probability to the presence in linseed of
antinutritional factors, such as mucilage, which can depress the retention of protein in chicks. # 2000
Elsevier Science B.V. All rights reserved.
Keywords: Linseed; Broiler chicks; Protein quality; Amino acid retention
1. Introduction
The seed of the ¯ax plant (Linum usitatissimum L.) is an important oilseed crop in
some countries as Canada, China, Argentina and India. Linseed contains approximately
*
Corresponding author. Tel.: ‡34-913943849; fax: ‡34-913943849.
E-mail address: [email protected] (J. TrevinÄo)
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 2 8 - 0
156
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
200±250 g kgÿ1 crude protein and 400±430 g kgÿ1 oil (Lee et al., 1991), constituting a
potential source of protein and energy to be used in animal feeding. It is also an excellent
source of omega-3 fatty acids, particularly a-linolenic acid, which are currently of
interest in both human and animal nutrition (Bhatty, 1995; Cunnane, 1995; Wood and
Enser, 1997; Doreau and Chilliard, 1997).
Linseed and solvent extracted seed meal (linseed meal) have been used predominantly
as a ruminant feed. Information on the nutritional value of linseed in broiler diets is
limited, and most studies relate to the effects of linseed on animal performance. Lee
et al. (1991) reported growth depression and reduced feed ef®ciency in chickens fed
diets containing 100 and 200 g linseed kgÿ1. Ajuyah et al. (1991) observed that birds
receiving a diet with 200 g linseed kgÿ1 had signi®cantly lower live weight than birds fed
other diets. Roth-Maier and Kirchgessner (1995) recommended a maximum of 50 g
linseed kgÿ1 to be used in broiler diets. Bond et al. (1997) observed that the inclusion
of linseed in the diet resulted in a signi®cant reduction in growth rate as the level of
linseed increased from 100 to 300 g kgÿ1, attributable to antinutritional factors including
mucilage, vitamin B6 antagonist (linatine), cyanogenic glycosides, trypsin inhibitors,
phytic acid, allergens and goitrogens (Madhusudhan et al., 1986; Bhatty, 1995).
The aim of the current program was to evaluate the protein quality of linseed with
growing broiler chicks using soybean meal (SBM) as a reference protein. The response
of chicks to dietary protein was determined in terms of protein ef®ciency ratio (PER), net
protein ratio (NPR) and apparent and true total tract retentions (ATTR and TTTR) for
nitrogen and amino acids.
2. Materials and methods
2.1. Materials
The linseed (golden variety, c. Royal) and SBM used in this study, were obtained as
single batches from commercial suppliers in Spain. Linseed was ground through a
ultracentrifuge mill with a 4 mm sieve before being incorporated into the experimental
diets. Linseed (LS) and (SBM) samples were analyzed in duplicate by the procedures
described below.
2.2. Experiment 1
In this experiment, the protein quality and SBM-replacement value of linseed were
evaluated using the PER and NPR bioassay.
Day-old male broiler chicks (Cobb) were fed a commercial starter diet from 0 to 7 days
post-hatching, after which they were assigned to the dietary treatments. A total of 60
chicks were distributed at random to ®ve treatments, in four groups of three birds each.
The mean group initial weights were similar (111.0 g). All the chicks were housed in an
environmentally controlled room in heated, thermostatically controlled starter batteries
with raised wire ¯oors. Feed and water were offered ad libitum and light was provided
continuously. The test diets were fed from 8 to 17 days post-hatching. The feed intake and
weight for each replicate were recorded.
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
157
Table 1
Composition (g kgÿ1) of diets used in Experiments 1 and 2
Experiment 1
Experiment 2
Proteinfree
SBM
SBM±
10LS
SBM±
30LS
LS
SBM
SBM±
10LS
SBM±
30LS
Ingredients
Soybean meal
Ground linseed
Starch
Glucose
Cellulose
Sun¯ower oil
Dicalcium phosphate
Calcium carbonate
Sodium chloride
Antioxidant (BHT)
Premixa
204.9
±
340.5
340.0
20.0
50.0
20.0
15.0
5.0
1.5
4.0
183.6
40.9
330.0
330.0
20.0
50.0
20.0
15.0
5.0
1.5
4.0
142.8
122.8
310.0
318.9
20.0
40.0
20.0
15.0
5.0
1.5
4.0
±
411.0
273.5
260.0
10.0
±
20.0
15.0
5.0
1.5
4.0
341.0
±
293.5
280.0
10.0
30.0
20.0
15.0
5.0
1.5
4.0
307.0
68.5
274.0
270.0
10.0
25.0
20.0
15.0
5.0
1.5
4.0
239.0
205.0
244.5
256.0
ÿ
10.0
20.0
15.0
5.0
1.5
4.0
±
±
432.5
442.0
40.0
40.0
20.0
15.0
5.0
1.5
4.0
Composition
Crude proteinb
ME (MJ kgÿ1 diet)c
91.0
14.2
91.3
14.2
90.2
14.3
90.3
14.4
152.2
13.1
149.4
13.2
149.4
13.3
3.2
14.8
a
Vitamin and mineral mixture provided (mg kgÿ1 diet): calcium carbonate, 14 g; dicalcium phosphate, 20 g;
sodium chloride, 4.2 g; retinol, 3 mg; cholecalciferol, 55 mg; dl-tocopheryl acetate, 25 mg; menadione, 2.5 mg;
thiamine, 3 mg; ribo¯avin, 6 mg; pyridoxine, 7.5 mg; folic acid, 0.2 mg; cyanocobalamin, 0.02 mg; biotin,
0.2 mg; calcium pantothenate, 25 mg; niacin, 50 mg; choline chloride, 1300 mg; CuSO45H2O, 29.5 mg;
FeSO47H2O, 375.0 mg; ZnSO4H2O, 138.0 mg; MnSO4H2O, 277.0 mg; Na2SeO3, 0.35 mg; KI, 0.20 mg;
CoCl26H2O, 2.1 mg; Na2MoO42H2O, 0.50 mg and BHT, 1.5 g.
b
Determined values.
c
Calculated values. ME attributed to linseed, 15.7 MJ kgÿ1 (Lee et al., 1991). SBM: Soybean meal; SBM10LS: Linseed protein replacing SBM protein by 10%; SBM-30LS: Linseed protein replacing SBM protein by
30% and LS: Linseed.
The ®ve dietary treatments consisted of a protein-free diet and four test diets containing
the following protein sources: reference SBM diet, and SBM diet modi®ed to contain
10 (SBM-10LS diet), 30 (SBM-30LS diet) and 100% (LS diet) of the total crude protein
from linseed. The test diets were formulated to contain 90 g crude protein kgÿ1, the
concentration of ground linseed being increased by decreasing the amount of SBM,
glucose and starch in the reference diet. The composition of experimental diets appears
in Table 1.
2.3. Experiment 2
The objective of this experiment was to estimate the effect of replacement in part
of SBM protein by linseed protein on the ATTR and TTTR for nitrogen and amino
acids.
Day-old male broiler chicks (Cobb) were maintained on a commercial diet until the
beginning of the trial. On the 28th day, 48 birds of similar weight were randomly divided
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
158
into 16 groups of three chickens each. Four such groups were assigned to each of the
following dietary treatments: protein-free diet and three test diets in which 0 (SBM diet),
10 (SBM-10LS diet) and 30% (SBM-30LS diet) of the SBM protein was replaced by
linseed protein. A diet containing linseed as the sole source of protein was not tested
due to the very poor performance of chicks fed on the LS diet in experiment 1. A protein
level of 150 g kgÿ1 diet, which is approximately 25% lower than that recommended
for broilers from 3 to 6 weeks of age (National Research Council, 1994), was chosen
since it was thought that a suboptimal protein level would result in a greater effect
of the quality of protein provided. The composition of the experimental diets is given
in Table 1.
Diets were evaluated in a balance trial by the total collection procedure. After 3 days of
adaptation, birds were starved for 24 h, then fed on experimental diets ad libitum for 3
days and starved again for the following 24 h. Feed intake and excreta output for each
cage were measured quantitatively. Excreta samples were collected twice daily and
frozen; at the end of the balance period, they were freeze-dried, weighed and ground to
pass a 1 mm sieve.
2.4. Analyses
Dry matter, crude protein (Kjeldahl N6.25), crude ®ber, ether extract and ash were
analyzed using the standard methods of the Association of Of®cial Analytical Chemists
(AOAC International, 1995). Neutral-detergent ®ber was determined as described by Van
Soest et al. (1991), acid-detergent ®ber and acid-detergent lignin following the sequential
procedure proposed by Robertson and Van Soest (1981). Mucilage content of the linseed
was estimated by extracting the seeds with boiling water (1:20, w:v) for 4 h; the extract
was precipitated by adding ethanol, separated by centrifugation and, ®nally, freeze-dried
(Mazza and Biliaderis, 1989; Bhatty, 1993). Amino acid analysis was performed by
HPLC after 22 h hydrolysis with boiling 6 N HCl under re¯ux conditions; nitrogen was
bubbled through the mixture during the hydrolysis period. A large acid:sample ratio
(400 ml:200 mg, v/w) was used to reduce amino acid losses in the presence of
carbohydrates. Protein hydrolyzates and amino acid calibration mixture were derivatized
by OPA-pthaldialdehyde and amino acids were measured in a HPLC system (HewlettPackard 1100, Waldbronn, Germany) following the procedure described by Jones et al.
(1981). Cystine was determined as cysteic acid (Moore, 1963) and tryptophan after
alkaline hydrolysis (AOAC International, 1995).
2.5. Calculations and statistics
PER and NPR were computed by the following formulas:
Gain body weight
Protein consumed
Weight gain of test group ÿ Weight loss of protein-free group
NPR ˆ
Protein consumed
PER ˆ
ATTR and TTTR (corrected for metabolic and endogenous losses) for nitrogen and amino
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
159
acids were calculated as follows:
TNC ÿ TNE
TNC
TNC ÿ …TNE ÿ TNEF†
TTTR ˆ
TNC
ATTR ˆ
where TNC is the total nutrient consumed, TNE the total nutrient excreta and TNEF the
total nutrient excreta of protein-free group.
Results obtained in the two experiments were subjected to regression analysis using the
linear and non-linear models (Statistical Analysis Systems Institute, 1988).
3. Results
The chemical and amino acid composition of linseed and SBM used in this study are
shown in Table 2. In general, the composition in essential amino acids of linseed
compared very well to that of reference SBM except for its low content of lysine.
Expressed as g amino acid 16 gÿ1 N, the concentration of lysine in linseed was about
Table 2
Composition (g kgÿ1 DM) of Soybean meal and linseed samples
Component
Soybean meal
Linseed
Crude protein (N6.25)
Ether extract
Crude ®ber
Neutral detergent ®ber
Acid detergent ®ber
Acid detergent lignin
Mucilage
Ash
Amino acids (g 16 gÿ1 N)
Aspartic acid
Glutamic acid
Serine
Histidine
Glycine
Threonine
Alanine
Arginine
Tyrosine
Valine
Methionine
Phenylalanine
Isoleucine
Leucine
Lysine
Cystine
Tryptophan
493.0
18.2
79.3
132.3
69.0
2.1
±
68.7
238.8
441.4
53.2
131.6
66.2
18.7
75.0
42.6
11.7
21.0
5.7
2.8
4.3
4.5
4.8
8.3
3.9
5.2
1.8
6.1
5.0
8.5
6.2
1.5
1.5
10.6
19.2
5.6
2.6
5.5
4.8
4.6
10.0
3.3
5.2
1.9
6.1
5.2
6.4
3.8
2.4
1.7
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
160
Table 3
Evaluation of protein quality and SBM replacement value of linseed (LS)a
Diet
Weight gain
Feed intake
Feed to gain ratio
SBM
SBM-10LSb
SBM-30LSc
LS
97.6
75.3
57.3
6.9
304.2
286.7
281.7
192.5
3.12
3.81
4.91
27.81
Reciprocal-Y
0.869
3.2210ÿ3
0.123103
Exponential
0.933
1.08
0.102
Regression analysis
Model
Square root-Y
R2
0.927
Intercept
9.62
S.E.
0.330
***
P-value
Slope
ÿ0.172
S.E.
0.0153
***
P-value
***
***
ÿ3
0.04610
0.005710ÿ3
***
0.056
0.0047
***
PERd
3.38
3.00
2.21
0.40
Square root-Y
0.944
1.84
0.049
***
ÿ0.030
0.0023
***
NPRd
4.29
4.05
3.26
1.96
Reciprocal-Y
0.950
2.2710ÿ1
0.108101
***
0.06910ÿ1
0.005010ÿ1
***
a
All values are the mean of four replicates of three birds from 8 to 17 days of age.
Linseed protein replacing SBM protein by 10%.
c
Linseed protein replacing SBM protein by 30%.
d
PER: protein ef®ciency ratio and NPR: net protein ratio.
***
P<0.001.
b
Table 4
Metabolic plus endogenous losses of nitrogen and amino acids in excreta (mg per bird per day) for growing
chicks fed a protein-free dieta
Mean
S.E.
Total N
184.1
20.26
Amino acids
Asp
Glu
Ser
His
Thr
Ala
Arg
Tyr
Val
Met
Phe
Ile
Leu
Lys
Cys
59.3
48.5
30.7
6.1
24.2
28.2
34.6
11.3
23.3
10.7
17.2
16.2
28.2
16.9
28.4
6.53
5.36
2.74
0.32
1.11
0.53
1.30
0.00
1.31
0.01
0.76
0.52
0.96
0.53
4.06
424.7
17.81
Total amino acids
a
Mean data from four pulled samples each from three animals S.E.
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
161
39% lower than the corresponding value for SBM. In contrast, linseed contained a
considerable higher amount of sulfur-containing amino acids (methionine plus cystine).
Results of the protein quality bioassay are presented in Table 3. The inclusion of
linseed in the reference diet depressed body weight gain and feed utilization (feed
intake:weight gain ratio). Regression analysis revealed a statistically signi®cant
(P<0.001) relationship between performance parameters and rate of linseed inclusion.
Of the models ®tted, the square root-Y for weight gain, reciprocal-Y for feed intake and
exponential for feed to gain ratio yielded the highest R2 values. These values (Table 3)
were 4.2, 3.7 and 14.0%, respectively, higher than the corresponding values obtained
applying the linear model. The results of PER and NPR were in accordance with the
performance data. Both conventional indexes ranked the protein sources in the same order
to that shown by performance data. The PER and NPR values obtained in the bioassay
also showed a statistically signi®cant (P<0.001) relationship with the inclusion level of
linseed in the diet. Curvilinear models were better ®tted to data than linear model, and
they explained 89.1 and 95.0% of the variability in PER and NPR, respectively.
Table 4 shows the metabolic plus endogenous losses of nitrogen and amino acids found
in the excreta of birds given the protein-free diet. Losses for individual amino acids varied
between 59.3 mg per bird per day for aspartic acid and 6.1 mg per bird per day for
histidine. The data on the total tract retention for nitrogen and individual amino acids are
Table 5
ATTR and TTTR coef®cients of nitrogen and amino acids for chicks fed diets containing SBM or SBM partly
replaced by linseed (SBM-10LSa and SBM-30LSb) as the sole source of proteinc
Diet
Apparent retention
True retention
SBM
SBM-10LS
SBM-30LS
SBM
SBM-10LS
SBM-30LS
Total N
0.549
0.465
0.413
0.657
0.577
0.538
Amino acids
Asp
Glu
Ser
His
Thr
Ala
Arg
Tyr
Val
Met
Phe
Ile
Leu
Lys
Cys
0.851
0.920
0.852
0.893
0.838
0.797
0.883
0.914
0.877
0.927
0.897
0.886
0.872
0.869
0.736
0.820
0.856
0.817
0.870
0.792
0.765
0.855
0.880
0.822
0.881
0.837
0.839
0.829
0.848
0.686
0.755
0.780
0.733
0.790
0.687
0.667
0.740
0.759
0.695
0.706
0.750
0.752
0.756
0.784
0.646
0.897
0.929
0.894
0.915
0.876
0.840
0.919
0.929
0.909
0.942
0.918
0.912
0.897
0.890
0.818
0.860
0.900
0.857
0.887
0.830
0.794
0.884
0.897
0.852
0.909
0.858
0.864
0.854
0.870
0.767
0.808
0.801
0.776
0.811
0.729
0.711
0.771
0.786
0.732
0.754
0.775
0.780
0.783
0.809
0.732
Total mean
0.867
0.827
0.733
0.903
0.859
0.767
a
Linseed protein replacing SBM protein by 10%.
Linseed protein replacing SBM protein by 30%.
c
All values are the mean of four replicates of three chicks.
b
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
162
summarized in Table 5. The ATTR for nitrogen and individual amino acids was impaired
by the inclusion of linseed in the SBM reference diet. For each amino acid, the ATTR
coef®cient decreased as the inclusion level of linseed in the SBM diet increased. Of the
amino acids considered essential to poultry, methionine followed by valine were the most
affected by the use of linseed. The TTTR coef®cients for nitrogen and single amino acids
were higher than those of the, respective values, for ATTR, and they were also markedly
lowered by the effect of linseed. In general, the decrease in the TTTR value for each
Table 6
Linear regression analysis relating ATTR and TTTR coef®cients of nitrogen and amino acids to rate of inclusion
of linseed in the diet
Coeficient
Total N
Amino acids
Asp
Glu
Ser
His
Thr
Ala
Arg
Tyr
Val
Met
Phe
Ile
Leu
Lys
Cys
Total mean
***
a
a
R2
Intercept
S.E.
P-value
Slope
S.E.
P-value
ÿ0.0364
ÿ0.0326
0.00245
0.00296
***
ÿ0.0079
ÿ0.0071
ÿ0.0106
ÿ0.0107
ÿ0.0097
ÿ0.0096
ÿ0.0086
ÿ0.0087
ÿ0.0124
ÿ0.0120
ÿ0.0107
ÿ0.0116
ÿ0.0122
ÿ0.0123
ÿ0.0129
ÿ0.0120
ÿ0.0149
ÿ0.0144
ÿ0.0185
ÿ0.0163
ÿ0.0118
ÿ0.0115
ÿ0.0109
ÿ0.0107
ÿ0.0094
ÿ0.0092
ÿ0.0071
ÿ0.0067
ÿ0.0057
ÿ0.0070
0.00158
0.00119
0.00083
0.00133
0.00110
0.00105
0.00100
0.00094
0.00130
0.00124
0.00124
0.00175
0.00105
0.00100
0.00133
0.00130
0.00106
0.00102
0.00198
0.00196
0.00096
0.00095
0.00086
0.00083
0.00088
0.00087
0.00099
0.00094
0.00122
0.00127
***
ÿ0.0107
ÿ0.0105
0.00096
0.00086
***
ATTR
TTTRa
0.957
0.924
0.550
0.649
0.0057
0.0069
***
ATTT
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
ATTR
TTTR
0.716
0.781
0.942
0.866
0.886
0.894
0.880
0.895
0.901
0.904
0.882
0.815
0.931
0.938
0.903
0.894
0.952
0.952
0.896
0.874
0.937
0.936
0.942
0.943
0.919
0.917
0.836
0.836
0.688
0.754
0.854
0.894
0.907
0.935
0.854
0.895
0.898
0.918
0.840
0.877
0.801
0.851
0.894
0.925
0.921
0.936
0.880
0.909
0.939
0.960
0.892
0.913
0.885
0.910
0.870
0.895
0.873
0.893
0.726
0.813
0.0183
0.0089
0.0062
0.0100
0.0082
0.0079
0.0075
0.0070
0.0097
0.0093
0.0093
0.0131
0.0079
0.0075
0.0100
0.0098
0.0079
0.0076
0.0149
0.0147
0.0072
0.0071
0.0064
0.0062
0.0066
0.0065
0.0074
0.0071
0.0092
0.0095
***
ATTR
TTTR
0.925
0.938
0.865
0.899
0.0072
0.0064
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
P<0.001.
In these cases square root-X model ®tted better than linear model.
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
163
amino acid was similar to that observed for the mean value of total amino acids.
Regression analysis was carried out with the ATTR and TTTR coef®cients for nitrogen
and amino acids against the rate of linseed inclusion. The results (Table 6) indicated a
signi®cant (P<0.001) effect of inclusion level. For nitrogen the response was curvilinear
for both ATTR and TTTR, the selected model explaining 95.7 and 92.4%, respectively, of
the variability found. For individual amino acids, however, the responses were linear,
explaining 92.5% (ATTR) and 93.8% (TTTR) of the variability for the total mean of
amino acids.
4. Discussion
The chemical and amino acid composition of linseed used in the current study is within
the range of published values (Mazza and Biliaderis, 1989; Barbour and Sim, 1991;
Bhatty, 1995; Lee et al., 1995). A comparison of the amino acid composition found for
linseed with the amino acid requirements of broiler chicks during the three weeks of age
(National Research Council, 1994), on the basis of g amino acid gÿ1 crude protein,
indicated that the most limiting amino acid was lysine, which just satis®ed 79% of the
nutritive requirements of chicks.
The biological data from Experiment 1 indicated that the protein quality of linseed
was in¯uenced by the level at which it is found in the diet. When fed as the sole source
of protein in a diet containing 90 g crude protein kgÿ1, linseed caused a drastic reduction
in the growth rate of chicks and also in the PER and NPR values compared to those
obtained for SBM. When linseed was used at a low level (replacing 10% of SBM protein
in the reference diet), weight gain was depressed but PER and NPR were unaffected. The
decrease observed in PER and NPR values with increasing level of linseed in the diet is
attributable more to lower ef®ciency of feed utilization than to reduced feed (protein)
intake. This is consistent with previous reports in which detrimental effects on growth and
feed ef®ciency of chickens were observed when linseed was used at dietary levels in
excess of 100 g kgÿ1 (Ajuyah et al., 1991; Lee et al., 1991; Bond et al., 1997).
Data for PER and NPR were further supported by the retention data for nitrogen and
amino acids determined with the fecal collection method in Experiment 2. The mean
values for ATTR and TTTR of amino acids of SBM are close to those reported by Green
and Kiener (1989) with adult male birds given a diet based on SBM and containing 144 g
crude protein kgÿ1 (ATTR and TTTR coef®cients of 0.85 and 0.92, respectively). The
replacement in part of the SBM protein by linseed protein resulted in a decrease of the
ATTR values for nitrogen and amino acids, and it was more marked as the replacement
level increased. As expected, the ATTR values for nitrogen were lower than those for
single amino acids as nitrogen retention measures the difference between dietary nitrogen
intake and nitrogen in excreta from both urinary and digestive tract origin. Urinary amino
acid excretion does not signi®cantly affect amino acid retention values since the major
nitrogen compounds in urine are uric acid or urates and ammonia, while amino acids are
presented in very small amounts (O'Dell et al., 1960; McNabb and McNabb, 1975). It
might also explain the current different response to inclusion level of linseed, which was
curvilinear for nitrogen and linear for all the amino acids. Data for glycine are not
164
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
presented since the formation of this amino acid from urinary uric acid and from
degradation of uric acid during acid hydrolysis of the excreta samples produces erratic
balance values (Soares et al., 1971; Slump et al., 1977).
Adjustment of apparent to true total tract retention of nitrogen and amino acids was
made by applying the values for metabolic plus endogenous losses determined using a
group of birds fed a protein-free diet. In this work, values for these losses were 184 and
425 mg per bird per day for total nitrogen and amino acids, respectively. These ®gures
agree with those reported by Salter et al. (1974) and Green and Kiener (1989). The TTTR
values were higher than the corresponding ATTR values for nitrogen and all the amino
acids in the test diets. However, correction of apparent to true total tract retention did not
in¯uence the order in which the diets could be ranked. As concluded from regression
analysis results (Table 6), the ATTR and TTTR data of each amino acid ®tted the same
regression line (that is, a linear mode), giving in most cases a similar precise estimation of
the effect produced by the rate of inclusion of linseed in the diet.
The results obtained in this work are evidence of poor utilization of linseed protein
compared to that of SBM. This may be attributable to the presence of various
antinutritional factors in linseed, the main ones being mucilage and linatine
(Madhusudhan et al., 1986; Bhatty, 1995). The mucilage content of the linseed used in
the current experiments was 75.0 mg kgÿ1 DM, which was similar to that reported by
Mazza and Biliaderis (1989) for another linseed cultivar. Linseed mucilage is a gumlike
material associated with the hull of linseed (BeMiller, 1986), which can reduce nutrient
availability in broiler chicks. It has been assumed that soluble ®bre constituents such as
gum or pectins and other polysaccharide substances increase the viscosity of the digesta,
and they reduce digestion and absorption of nutrients (Marquardt et al., 1979; Ward and
Marquardt, 1983; Angkanaporn et al., 1994). It is also suggested that the increased ¯ow
of undigested nutrients to the lower gut, as a result of the increased digesta viscosity,
stimulates bacterial activity and it leads to the proliferation of micro¯ora and to a greater
competition with the host animal for nutrients (Bedford, 1995; Choct et al., 1996).
Linatine, a dipeptide of glutamic acid and proline, has been reported to depress growth of
chickens as a vitamin B6 antagonist (Mandokhot and Singh, 1983; Bhatty, 1995). In the
current study, however, test diets were supplemented with 75 mg kgÿ1 pyridoxine, being
more than twice the estimated requirements of broiler chicks (3.5 mg kgÿ1 diet; National
Research Council, 1994). Consequently, there was probably suf®cient pyridoxine present.
In conclusion, the current study indicated that the utilization of protein from linseed by
broiler chicks was considerably worse than that from SBM. Performance of chicks, PER
and NPR and nitrogen and amino acid retention were impaired as the replacement level of
SBM protein by linseed protein increased, due primarily to a reduction in the retention of
nitrogen and amino acids caused probably by the presence of antinutritional factors, for
example mucilage, in linseed.
Acknowledgements
The authors gratefully acknowledge the ®nancial support given by the ComisioÂn
Interministerial de Ciencia y TecnologõÂa (Project AGF98-0688).
J. TrevinÄo et al. / Animal Feed Science and Technology 84 (2000) 155±166
165
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