Comparison of the nutritive value for laying hens of
diets containing azolla (
Azolla pinnata
) based on
formulation using digestible protein and digestible
amino acid versus total protein and total amino acid
A. Khatun
a, M.A. Ali
b,*, J.G. Dingle
baDepartment of Animal Husbandry, Hajee Md. Danesh Agriculture college, Bashirhat, Dinajpur, Bangladesh bSchool of Veterinary Science and Animal Production, Gatton College, University of Queensland, Lawes,
Qld 4345, Australia
Received 18 November 1997; received in revised form 24 November 1998; accepted 22 May 1999
Abstract
Azolla (Azolla pinnata) was assessed for nutrient content and feeding value in laying hen diets. Proximate analysis, together with the estimates of digestible protein, ADF, NDF and metabolizable energy indicated that it was a fair source of plant protein (285.4 g kgÿ1) with a digestible protein
value of 219.8 g kgÿ1
and a metabolizable energy value of 7.59 MJ kgÿ1
(906 g kgÿ1
DM). The feeding value of azolla in laying hens was studied in two feeding trials of 16 and 8 weeks duration, respectively. Azolla meal was included at a level of 50 or 100 g kgÿ1diet at the expense of sesame meal in diets formulated on a total protein and total amino acid, or digestible protein and digestible amino acid basis (Trial 1). In Trial 2, 150 and 200 g kgÿ1azolla meal was included in diets formulated using a total protein and total amino acid, or digestible protein and digestible amino acid basis. L-lysine HCl and DL-methionine were added to the diets formulated using digestible nutrients to adjust the digestible lysine and methionine contents to those in the wheat sesame meal based control diet.
It was found that azolla meal could replace sesame meal on a digestible protein and digestible amino acid basis up to 200 g kgÿ1
diet with egg production as the parameter, while it could replace only up to 150 g kgÿ1sesame meal in the diet based on total protein and total amino acids. Egg mass output and feed conversion ratio were significantly better with up to 200 g kgÿ1
azolla meal in the diet when included on a digestible protein and digestible amino acid basis but not when the diets were formulated on a total protein and total amino acid basis. Feeding azolla on a digestible protein
81 (1999) 43±56
*Corresponding author. Tel.: +61-754-601-251; fax: +61-754-601-444
E-mail address: maa@warigal.uqg.uq.edu.au (M.A. Ali)
0377-8401/99/$ ± see front matter#1999 Elsevier Science B.V. All rights reserved.
and digestible amino acid basis maintained or improved protein efficiency. Feeding azolla on a total or digestible nutrient basis had no affect on egg quality except egg size and yolk colour. Egg size improved when the diets were formulated on a digestible protein and digestible amino acid basis. Yolk colour was significantly improved with increasing levels of azolla meal and a longer period of feeding.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Azolla; Composition; Layers; Feeding value; Digestible protein; Digestible amino acid
1. Introduction
Azolla (Azolla pinnata) is an aquatic fern found abundantly in ponds, ditches and paddy fields in tropical and subtropical regions of the world. It contains 140±300 g kgÿ1
CP (Subudhi and Singh, 1978; Sreemannaryana et al., 1993) and can be used as a feed ingredient for ruminants and non-ruminants (Subudhi and Singh, 1978; Tamang and Samanta, 1993; Ali and Leeson, 1995). It is also a good source of pigments.
Nutritionists are now becoming interested in formulating diets on the basis of digestible protein and digestible amino acids (Vogt, 1988; Rhone Poulenc Animal Nutrition, 1989; Fernandez et al., 1995). The amino acid availability of feed ingredients varies depending upon processing, fibre content, protease inhibitors and the presence of complexes (Carpenter and Booth, 1973; Raharjo and Farrell, 1984; Han et al., 1991; Parsons et al., 1992). The performance of laying hens improved when the feed formulation was based on digestible lysine and digestible methionine concentration rather than total lysine and total methionine concentration (Bougon and Joly, 1990). Rostagno et al. (1995) demonstrated that there was considerable benefit in feeding cheap by-products to broilers when diets were balanced with respect to digestible amino acids. It has been demonstrated that the digestible lysine or methionine measured in roosters reasonably reflects the availability of the respective amino acid in a chick growth assay (Han et al., 1991; Parsons et al., 1992). Ali and Leeson (1995) found lower digestible protein and amino acids in azolla meal than in rice polish and snail meal. Reports on the feeding value of azolla in the diet of laying hens are scanty. Variation in composition and lack of information of azolla meal makes incorporation in the diet of laying hens more difficult.
The present study was therefore undertaken to determine the chemical composition, metabolizable energy and digestible protein contents and subsequently the feeding value of azolla meal on a total protein and total amino acid basis, compared with a digestible protein and digestible amino acid basis for laying hens.
2. Materials and methods
2.1. Feed source
Fresh azolla was harvested from local ponds and then sun-dried. It was ground (4 mm screen) and stored in air-tight plastic bags until used.
2.2. Metabolizable energy
The apparent metabolizable energy value of azolla was calculated by the chemical method of Sibbald et al. (1963).
2.3. Protein digestibility
Protein digestibility of azolla meal was measured by including the ingredient at 200 g kgÿ1
as the sole source of protein in a purified diet, together with a control diet which was essentially nitrogen-free (McNab and Shannon, 1972) except that some sawdust was incorporated instead of alphafloc (cellulose). The composition of the diets is shown in Table 1. Chromic oxide was added at a level of 5 g kgÿ1
diet as an indigestible marker.
Each diet was fed ad libitum to ten 12-week-old Rhode Island Red cockerels. The birds were given an adjustment period of 5 days on the diet. On day 6, birds were killed by cervical dislocation. Immediately after death, the abdomen was opened and the ileum removed. Digesta were collected from the fifth segment of the ileum, about 10 cm anterior to the ileo-caecal junction to avoid potential contamination with urine. Protein digestibility was calculated by the method of Lodhi et al. (1970) with endogenous N correction determined from chickens fed the nitrogen-free diet.
2.4. Diet formulations
Diets were formulated on a total protein and total amino acids versus digestible protein and digestible amino acids basis. Nutrients in the diets were adjusted close to the requirements of brown egg layers (NRC, 1994) while the digestible protein and digestible lysine contents were similar to Vogt (1988). Digestible protein content was calculated from the analysed crude protein values of the ingredients and from their digestibility coefficients of protein/nitrogen except for azolla which was the determined value. The digestible amino acid contents of the ingredients were calculated from the digestibility
Table 1
Composition of experimental diets for determination of protein digestibility in layers
Ingredients Purified diets (g kgÿ1)
A B
Starch 757.5 897.5
Azolla 200 ±
Sawdust 10 60
Bone meal 25 35
Salt 5 5
Vitamin mineral premixa 2.5 2.5
aVitamin mineral premix provided per kg diet: vitamin A 12,000 IU; vitamin D
32000 IU; vitamin E 15 IU;
vitamin K32 mg; vitamin B11 mg; vitamin B24 mg; vitamin B63 mg; nicotinic acid 25 mg; pantothenic acid
12mg; vitamin B120.01 mg; folic acid 0.5 mg; biotin 0.05 mg; cobalt 0.4 mg; copper 8 mg; iron 32 mg; iodine
0.05 mg; manganese 64 mg; zinc 40 mg; selenium 0.16 mg; choline chloride 250 mg.
coefficients of amino acid and total amino acid values of the ingredients (NRC, 1994) except for processed full-fat-soybean (Scragg, 1994) and azolla meal (Ali and Leeson, 1995) with adjustment for the increased protein content of our azolla meal. The digestibility coefficients of nitrogen and amino acids used were those found for wheat and processed full-fat-soybean (Scragg, 1994) sesame meal (NRC, 1994) rice polishings and azolla meal (Ali and Leeson, 1995) with adjustment of the amino acid digestibility coefficients for the increased nitrogen digestibility of azolla meal.
2.5. Layer trials
The feeding value of azolla meal was determined in two feeding trials using 579 Shaver Starcross commercial layers. In Trial 1, diets were prepared by including azolla meal at a level of 50 and 100 g kgÿ1
formulated on a total protein and total amino acid basis, and on a digestible protein and digestible amino acid basis by replacing some sesame meal and full-fat-soybean to adjust the digestible protein, and digestible lysine and methionine (Table 2).
In Trial 2, diets were prepared with 150 and 200 g kgÿ1azolla meal on the same basis as in Trial 1. Synthetic L-lysine HCl and DL-methionine were added to the diets formulated on a digestible nutrient basis to adjust the digestible lysine and methionine contents (Table 3).
In Trial 1, 60 laying pullets 43-week-old and in Trial 2, 80 laying pullets 28-week-old were used. In Trial 1, each diet was applied to three replications of four birds, while in Trial 2, each diet was applied to four replications of four birds. The birds were reared in individual cages in an open house. All mash dry feed was supplied ad libitum throughout the experimental period. 16 h light was maintained during the experimental periods. Prior to the experiment all birds were adjusted in cages for 2 weeks with a common layer diet. The experiments continued for 16 and 8 weeks for Trials 1 and 2, respectively.
During the experiments, daily egg production, egg weight and weekly feed consumption were recorded. In Trial 1, one egg from each replicate was collected for the first 3 days and last 3 days of weeks 4, 8, 12 and 16 and in Trial 2, one egg from each replicate was collected on the last 3 days of weeks 4 and 8 to determine egg quality. The eggs were weighed after collection. The external egg quality characteristics measured were shape index (Reddy et al., 1979) egg shell breaking strength (Ar et al., 1979) shell surface area (Carter, 1975) per cent shell and shell thickness. The internal egg quality characteristics measured were Haugh Unit (Haugh, 1937) albumen index (Heiman and Carver, 1936) albumen dry matter, yolk colour score (Roche Yolk Colour fan) yolk index (Wesley and Stadelman, 1959) and yolk dry matter. Hen-day egg production, egg mass output and feed conversion ratio (feed consumed per unit of egg mass produced) were determined from the recorded data. Protein efficiency ratio was calculated as per Nagra and Virk (1986) using the value of 0.12 g protein in 1 g whole egg (Lodhi et al., 1980).
2.6. Chemical analysis
Azolla meal was analysed for proximate composition using standard procedures (AOAC, 1990). Acid detergent fibre (ADF) and neutral detergent fibre (NDF) were
determined by the methods of Goering and Van Soest (1970). The starch content of azolla was determined by the method of Lane and Eynon (1923). Free sugar was estimated by a colorimetric method (Dubois et al., 1951). Chromic oxide content in feed and excreta was measured using the method described by Hill and Anderson (1958).
2.7. Statistical analysis
Data were subjected to analysis of variance (Steel and Torrie, 1980) and significant differences between treatments were identified by least significant difference.
3. Results and discussion
3.1. Chemical composition
Air dried azolla meal was analysed for its nutrient content. It contained dry matter (905.89 g kgÿ1) which was similar to Ali and Leeson (1995) and Tamang and Samanta
Table 2
Composition of layer diets containing graded levels of azolla meal (Trial 1)
Ingredients Level of azolla meal (g kgÿ1)
0 (Control) 50 (TPTAa) 50 (DPDAb) 100 (TPTA) 100 (DPDA)
Wheat 490 490 470 480 470
Rice polish 190 190 180 180 180
Sesame meal 115 95 110 65 70
Full-fat soybean (processed) 120 90 105 90 95
Azolla meal ± 50 50 100 100
Oyster shell 65 65 65 65 65
Bone meal 15 15 15 15 15
Salt 5 5 5 5 5
Vitamin mineral premixc + + + + +
Nutrient composition (fresh basis)
Crude protein (g kgÿ1) 178.7 174.0 180.9 176.0 178.5
Digestible protein (g kgÿ1) 156.3 150.2 156.6 150.3 152.6
Total lysine (g kgÿ1) 7.87 7.05 7.55 6.88 7.24
Digestible lysine (g kgÿ1) 6.72 5.95 6.36 5.69 5.95
Total methionine (g kgÿ1) 3.80 3.48 3.73 3.15 3.44
Digestible methionine (g kgÿ1) 3.42 3.09 3.32 2.74 3.04
ME (MJ kg±1) 11.57 11.35 11.33 11.20 11.20
Crude fibre (g kgÿ1) 47.6 50.6 50.9 53.7 54.7
Calcium (g kgÿ1) 32.1 32.2 32.5 32.3 32.8
Av. phosphorus (g kgÿ1) 3.5 3.4 3.5 3.4 3.5
aTPTA = Total protein and total amino acids.
bDPDA = Digestible protein and digestible amino acids.
cVitamin mineral premix provided per kg diet: vitamin A 12,000 IU; vitamin D
32000 IU; vitamin E 15 IU;
vitamin K32 mg; vitamin B11 mg; vitamin B24 mg; vitamin B63 mg; nicotinic acid 25 mg; pantothenic acid
12 mg; vitamin B120.01 mg; folic acid 0.5 mg; biotin 0.05 mg; cobalt 0.4 mg; copper 8 mg; iron 32 mg; iodine
0.05 mg; manganese 64 mg; zinc 40 mg; selenium 0.16 mg; choline chloride 250 mg.
(1993). Crude protein (285.4 g kgÿ1
) was similar to sesame meal (Rahman, 1992) and grain legumes (Rahman, 1981). The analysed crude protein content of azolla was similar to the values reported by Buckingham et al. (1978) and Singh et al. (1983) but higher than the values reported by others (Tamang and Samanta, 1993; Ali and Leeson, 1995). Digestible protein (219.8 g kgÿ1) was higher than the values of Tamany et al., (1992) and Ali and Leeson (1995). Crude fibre (123.8 g kgÿ1) was similar to the values reported by Sreemannaryana et al. (1993) and Ali and Leeson (1995) but slightly higher than the values of Subudhi and Singh (1978) and lower than the values of Querubin et al. (1986) and Tamang and Samanta (1993). ADF (334.1 g kgÿ1
) was similar to the values reported by Buckingham et al. (1978) but lower than those of Tamang and Samanta (1993) and Ali and Leeson (1995). NDF (445.7 g kgÿ1
) was lower than the reported value of others (Querubin et al., 1986;Tamang and Samanta, 1993; Ali and Leeson, 1995). Ash (169.2 g kgÿ1
)was lower than most reports (Singh et al., 1983; Querubin et al., 1986; Tamang and Samanta, 1993; Ali and Leeson, 1995) but similar to that of Buckingham
Table 3
Composition of layer diets containing graded levels of azolla meal (Trial 2)
Ingredients Level of azolla meal (g kgÿ1)
0 (Control) 150 (TPTAa) 150 (DPDAb) 200 (TPTA) 200 (DPDA)
Wheat 490 447 432.45 428 404.9
Rice polish 190 160 140 145 140
Sesame meal 115 60 75 50 55
Full-fat Soybean (Processed) 120 75 90 60 80
Azolla meal ± 150 150 200 200
Oyster shell 65 65 65 65 65
Bone meal 15 15 15 15 15
Crude protein (g kgÿ1) 178.7 175.0 182.2 175.0 183.0
Digestible protein (g kgÿ1) 156.3 148.0 155.3 146.5 154.0
Total lysine (g kgÿ1) 7.87 6.41 7.67 6.35 8.00
Digestible lysine (g kgÿ1) 6.72 5.24 6.70 5.14 6.72
Total methionine (g kgÿ1) 3.80 3.11 3.89 3.03 3.82
Digestible methionine (g kgÿ1) 3.42 2.67 3.44 2.56 3.42
ME (MJ kg±1) 11.57 11.57 11.57 11.57 11.57
Crude fibre (g kgÿ1) 47.6 56.3 55.8 59.1 59.6
Calcium (g kgÿ1) 32.1 32.8 33.1 33.2 33.4
Av. phosphorus (g kgÿ1) 3.5 3.5 3.5 3.5 3.5
aTPTA = Total protein and total amino acids.
bDPDA = Digestible protein and digestible amino acids.
cVitamin mineral premix provided per kg diet: vitamin A 12,000 IU; vitamin D
32000 IU; vitamin E 15 IU;
vitamin K32 mg; vitamin B11 mg; vitamin B24 mg; vitamin B63 mg; nicotinic acid 25 mg; pantothenic acid
12 mg; vitamin B120.01 mg; folic acid 0.5 mg; biotin 0.05 mg; cobalt 0.4 mg; copper 8 mg; iron 32 mg; iodine
et al. (1978). The metabolizable energy (7.59 MJ kgÿ1
) was comparable to that of duck weed (Akter, 1995) but higher than reported previously for azolla meal (Ali and Leeson, 1995). These differences indicate that the azolla meal used in these trials was of a higher quality.
3.2. Egg production
The performance of laying hens in Trial 1 and 2 is shown in Tables 4 and 5 respectively. Feeding azolla meal on a digestible protein and digestible amino acid basis produced better egg production than with the control diet or diets formulated on a total protein and total amino acid basis. Hen-day egg production with 50 g kgÿ1
azolla meal using digestible protein and digestible amino acid was improved by 6.4 and 9.9% over the control diet and the diet with 50 g kgÿ1
azolla meal on total protein and total amino acids (Trial 1) while with 100 g kgÿ1
azolla meal on digestible protein and digestible amino acid egg production improved by 2.0 and 5.7% over the control diet and 100 g kgÿ1
azolla meal on total protein and total amino acid. However, those effects were not significant atp< 0.05. In Trial 2, hen-day egg production of birds fed 200 g kgÿ1azolla meal on total protein and total amino acid was significantly lower than that of hens fed the control diet or 150 or 200 g kgÿ1 azolla meal on digestible protein and digestible amino acid basis. These results indicate that azolla meal can be used up to 150 g kgÿ1on a total protein and total amino acid basis for laying hen but egg production was reduced at 200 g kgÿ1level. The results are consistent with those of Bastian (1987) but disagree with those of Singh and Subudhi (1978). However, when azolla meal was fed at 150 and 200 g kgÿ1
on a digestible protein and digestible amino acid basis egg production significantly improved by 5.5 and 4.3% over that obtained when azolla meal was fed at 150 and 200 g kgÿ1
on a total protein and total amino acid basis. Better egg production in diets formulated on digestible protein and digestible amino acid basis might be due to better precision of diet formulation. These results suggest that azolla meal can replace sesame meal on a digestible protein and digestible amino acid basis at up to 200 g kgÿ1
diet of laying hens but only to 150 g kgÿ1
diet when the diet is formulated on a total protein and total amino acid basis.
3.3. Egg mass output
The egg mass output (g egg/day) of hens fed diets with 50 and 100 g kgÿ1
azolla meal on a digestible protein and digestible amino acid basis improved over the control diet and diets formulated with a similar level of azolla meal on a total protein and total amino acid basis (Trial 1). However, the differences were not significant (p> 0.05). At 150 and 200 g kgÿ1
azolla meal fed on a digestible protein and digestible amino acid basis the egg mass output significantly improved over the control diet and 150 and 200 g kgÿ1
azolla meal on a total protein and total amino acid basis (Trial 2). The results confirm earlier observations of improved egg mass output in laying hens when fed diets formulated on the basis of digestible protein and digestible amino acids (Bougon and Joly, 1990; Joly, 1994).
Table 4
Performance of laying hens fed a diet containing 50 or 100 g kgÿ1azolla meal on the basis of total protein and total amino acids, or digestible protein and digestible
amino acids (Trial 1)a
Performance (MeanSE) Level of azolla meal (g kgÿ1) CV
(%)
Lsd values and level of significance
0 (Control) 50 (TPTA) 50 (DPDA) 100 (TPTA) 100 (DPDA)
Hen-day egg production (%) 75.73.5 72.20.8 82.12.2 72.05.3 77.71.0 6.3 NS
Egg mass output (g egg/bird/day) 49.52.5 48.31.4 52.71.5 47.32.6 50.90.4 5.4 NS
Feed consumption (g/bird/day) 118.52.8 118.63.6 119.41.4 118.22.0 119.20.4 3.5 NS
Feed efficiency 2.420.66 2.470.01 2.280.04 2.520.13 2.360.16 4.13 NS
PER 28.10.3 b 26.40.1 c 29.50.4 a 26.30.3 c 27.90.2 b 1.7 1.3*
Livability (%) 100.0 100.0 100.0 100.0 100.0 NS
aMeans in the rows bearing similar letters do not differ significantly.
*p< 0.05.
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Table 5
Performance of laying hens fed a diet containing 150 or 200 g kgÿ1azolla meal formulated on the basis of total protein and total amino acids, or digestible protein and
digestible amino acids (Trial 2)a
Performance (MeanSE) Level of azolla meal (g kg±1) CV (%) Lsd values and level
of significance
0 (Control) 150 (TPTA) 150 (DPDA) 200 (TPTA) 200 (DPDA)
Hen-day production (%) 73.51.3 ab 70.81.3 bc 76.30.4 a 69.41.1 c 73.70.9 ab 2.7 3.0*
Egg mass output (g egg/day) 39.60.7 c 38.21.1 c 44.50.2 a 38.90.5 c 42.10.5 b 3.0 1.9*
Feed consumption (g/bird/day) 107.32.2 c 112.61.5 ab 108.21.2 bc 113.60.6 a 107.31.3 c 2.9 4.9**
Feed efficiency 2.750.09 b 2.990.07 a 2.430.03 c 2.950.03 a 2.560.03 c 4.07 0.16*
PER 25.10.9 bc 23.20.6 c 27.50.3 a 22.90.3 c 26.10.3 ab 4.2 2.3*
Livability (%) 100.0 100.0 100.0 100.0 100.0 NS
aMeans in the rows bearing similar letters do not differ significantly.
*p< 0.05.**p< 0.01.
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3.4. Feed consumption
Feed consumption was similar in all dietary treatments in Trial 1 but it significantly increased for hens fed diets with 150 and 200 g kgÿ1azolla meal on a total protein and total amino acids basis compared with hens fed the control diet in Trial 2. Feed consumption of birds fed diets containing 150 and 200 g kgÿ1azolla meal on a digestible protein and digestible amino acid basis was similar to that of birds fed the control diet. The results partially agree with Querubin et al. (1986) who observed increased feed consumption of birds fed diets containing up to 150 g kgÿ1
azolla meal on a total protein and total amino acid basis but they disagree with those of Bastian (1987).
3.5. Feed efficiency
It is evident from Tables 4 and 5 that better feed efficiencies were found when azolla meal was fed at 50 and 100 g kgÿ1(Trial 1) but significantly improved over the control when fed at 150 and 200 g kgÿ1when formulated on a digestible protein and digestible amino acid basis (Trial 2) but it was poorer when the diets were formulated on a total protein and total amino acid basis. Improved feed efficiency in diets formulated on a digestible nutrient basis is mainly due to better egg production. The results are similar to earlier observations (Bougon and Joly, 1990; Johnson, 1992; Joly, 1994) of higher feed efficiency when fed on a digestible nutrient basis and confirm the reduced feed efficiency found in a broiler study (Querubin et al., 1986) when they were formulated on a total protein and total amino acids basis.
3.6. Protein efficiency ratio
Protein efficiency ratio (PER) improved (p< 0.05) for the 50 and 150 g kgÿ1
azolla meal diet formulated on the basis of digestible protein and digestible amino acid compared with the PER of the control diet or the diets with a similar level of azolla meal and formulated on the basis of total protein and total amino acid (Tables 4 and 5). PER for 100 and 200 g azolla meal on a digestible protein and digestible amino acid basis improved (p< 0.05) when compared to similar levels of azolla meal on a total protein and total amino acid basis but was similar to the control diet. Feeding azolla meal on a digestible protein and digestible amino acid basis maintained or improved protein efficiency but it was significantly reduced when fed on total protein and total amino acid basis.
3.7. Livability
No bird died in any treatment during the experiments indicating that azolla meal had no deleterious effect on livability. The results were consistent with Singh and Subudhi (1978) and Castillo et al. (1981) who found no effect on the livability of chicks and broilers.
Egg quality characteristics of laying hens fed diets containing azolla meal formulated on the basis of total protein and total amino acids, or on digestible protein and
digestible amino acids basis (Trials 1 and 2)a
Egg quality Experiment
(DPDA) values and levelof significance
Egg weight (g) 1 1st 62.10.5 63.30.8 61.91.5 62.62.1 63.10.7 0.5 NS
aValues in the rows bearing similar letters do not differ significantly.
3.8. Egg quality
The external and internal characteristics of eggs in feeding Trials 1 and 2 are presented in Table 6. It is evident that, apart from egg weight and yolk colour, egg quality characteristics were not affected by the dietary treatments. Feeding azolla meal on a digestible protein and digestible amino acid basis improved egg weight (Trial 2). The improved egg size for diets formulated on a digestible nutrient basis might be due to better critical amino acid balance (Morris and Gous, 1988). The results were similar to the earlier observations of Bougon and Joly (1990) and Joly (1994). The yolk colour significantly improved with increasing levels of azolla meal and period of feeding whether fed on a total or on a digestible protein and amino acid basis. These results were similar to the observations of Singh and Subudhi (1978) and Bastian (1987).
The results of our study indicated that azolla meal was a fair source of plant protein and metabolizable energy for laying hens. When azolla meal replaced sesame meal (wt./ wt.) on a digestible protein and digestible amino acid basis performance was improved over that obtained when the replacement was on the basis of total protein and amino acids.
Acknowledgements
We gratefully acknowledge the provision of facilities by the Department of Poultry Science, Bangladesh Agricultural University, Mynensingh, Bangladesh. The help of Mr. S. C. Das during the experiments is greatly appreciated.
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