Livestock Research for Rural Development 7 (3) 1995

Citation of this paper

Effect of replacing whole boiled soya beans with azolla in the diets of growing ducks

Maricel Becerra (1), T R Preston (1) and B Ogle (2)

(1) Centro para la Investigacion en Sistemas Sostenibles de Produccion Agropecuaria (CIPAV). AA20591 Cali, Colombia ( E-mail: cipav@cipav.org.co)
(2) Department of Animal Nutrition and Management, Box 7024, Swedish University of Agricultural Sciences, S-750 Uppsala Sweden

Abstract

Two feeding trials were carried out to determine the effect of feeding Azolla microphylla as partial replacement of the protein in boiled soya bean in diets based on sugar cane juice for meat ducks. The experimental design for the trials involved five treatments, four replications (pens) and 10 birds per pen. Diets, containing five levels of crude protein, which were formulated from boiled soya beans and Azolla microphylla and with sugar cane juice ad libitum as the energy source, were fed to 200 growing ducks (Cherry Valley hybrids). The rations were fed from one month of age until the birds reached 60 to 70 days of age, when two ducks (one male and one female) per pen were slaughtered for carcass evaluation.

In the first trial, actual intakes of Azolla were lower than expected, and supplied 15.2, 17.9, 24.4, and 30.3% of the total protein in diets Az15, Az30, Az45, and Az60, respectively. Daily gains (g) were 28.6, 30.4, 28.3, 24.1, and 21.4 for the control, Az15, Az30, Az45, and Az60 diets, respectively and decreased with level of azolla when this exceeded 15% of the dietary protein (P<0.001). Feed conversion ratios deteriorated with increasing consumption of Azolla (P<0.001).

In the second trial, actual intakes of Azolla were also lower than expected, and supplied 14.7, 17.5, 19.2, and 22.6% of the total protein in diets Az15, Az25, Az35, and Az45, respectively. Gains (g/day) were 32.6, 31.5, 30.2, 28.2, and 24.1 for the control, Az15, Az25, Az35, and Az45 diets, with decrease in gain with azolla level beyond15% of the protein (P<0.001). Feed conversion ratios increased with increasing consumption of Azolla (P<0.001). All the carcass traits were similar for all treatments in both trials.

Key words: Azolla, growing ducks, protein, sugar cane juice, feed conversion.

Introduction

Aquatic plant species, because of their growth habit, appear not to accumulate secondary plant compounds and therefore offer a greater potential than tree leaves as a source of protein for monogastric animals. Of these species the water fern Azolla, which grows in association with the blue-green alga Anabaena azollae, is perhaps the most promising from the point of view of ease of cultivation, productivity and nutritive value (Lumpkin and Plucknett 1982; Van Hove and López 1983).

The concept of using aquatic plants for different purposes is now receiving special attention. Azolla is one of the plant resources with high biomass and protein production. Little information is available on maximum levels of inclusion in the diets of ducks and for this reason two trials were carried out in which different amounts of whole boiled soy ad libitum. In the first trial intakes of boiled soya bean were adjusted weekly according to mean pen liveweight, while in the second trial the daily a bean were given, and Azolla and sugar cane juice supplied allowance of boiled soybeans was fixed throughout the trial.

Azolla is an aquatic fern genus, with six species distributed widely throughout warm-temperate and tropical zones. Its most remarkable feature is its symbiotic relationship with the nitrogen-fixing blue-green alga Anabaena azollae within its leaf cavities (Reynaud and Franche 1987). Azolla has been used for centuries in Asia as green manure, as a fertilizer for rice fields and supplement in diets for pigs, poultry and fish (Moore 1969; Cassani 1981; Lumpkin 1984). Some strains of Azolla can fix as much as 2-3 kg of nitrogen/ha/day. Azolla contains around 27% crude protein and 10% carbohydrates on a dry weight basis (Pullin and Almazan 1983).

Azolla is widely distributed and is found in ponds, ditches and channels containing stagnant water with a temperature range of 15- 350 Celcius (Singh and Subudhy 1978). It grows in aquatic habitats and absorbs nutrients mainly from water. In shallow water the plant roots attach to the soil and absorb nutrients from the soil.

Poultry, particularly ducks and chickens, can be raised on a diet including fresh Azolla. It has long been recognized as a feed for wildfowl in the USA and for domesticated ducks in China. It is reported to be fed to domestic fowl in Vietnam (Vo Minh Kha and Tran Quang Thuyet 1970).

In India, Subudhi and Singh (1978) concluded that fresh Azolla could replace about 20% of commercial feed in the diet of young chickens. They estimated that to replace this much commercial feed would require about 9 kg of fresh Azolla each day for 100 chickens and that this amount could be produced in a shallow pond 60 m² in area.

Materials and methods

Experimental design and birds

The experimental design, housing and management were identical in both trials. The experiments were conducted between March and June 1993, in the dry season. Two hundred 4 week old ducklings with initial liveweights of between 700 and 750 g were used in each experiment. The birds were identified and then individually weighed initially and at slaughter, and then by group once per week throughout the experiment. They were allocated to five treatments with four replications per treatment, and 10 birds per group. The initial total body weight of the ducks in each treatment was approximately the same. The experimental period was preceded by a preliminary period of one week.

Housing and management

The ducks were housed in a shed divided into pens constructed from bamboo, with thatched roofs and rice straw covered packed earth floors, with an average density of five ducks/m². During the daytime the birds also had access to outside sand yards (one duck/m²), and for approximately six hours per day to a fresh water swimming area (five ducks/per m²).

Feeders and drinkers were round plastic basins (40 cm diameter, 10 cm deep). Natural light only was used in the day time, and electric bulbs (4 w/m² of floor area) at night from hatching until the end of the experiment. The mean diurnal temperature during the experiment was around 30°C.

Diets and feeding

The ducklings were fed a commercial type starter diet between 15 and 32 days of age, and then were allocated at random to one of the experimental diets. The birds were group-fed different amounts of soya beans adjusted according to liveweight. The experimental diets were all based on reconstituted sugar cane juice offered ad libitum as the major energy source, with varying amounts of Azolla and whole boiled soya beans as the protein source. Total crude protein requirements were estimated from NRC recommendations (NRC 1984) and pilot trials were carried out to determine feed intakes for increasing liveweights. Daily boiled soya bean allowances were calculated so that Azolla offered ad libitum would supply approximately 0 (control), 15, 30, 45 or 60% of the daily crude protein intake (Table 1). A vitamin-mineral premix (0.5% of the diet) and common salt (0.25% of the diet) were mixed with the whole boiled soybeans.

Table 1: Composition of the diets
BLGIF.GIF (44 bytes)
N x 6.25 from soya Fresh Azolla Cane juice
BLGIF.GIF (44 bytes)
Control 100 - ad lib.
Az15 85 ad lib. ad lib.
Az30 70 ad lib. ad lib.
Az45 55 ad lib. ad lib.
Az60 40 ad lib. ad lib.
BLGIF.GIF (44 bytes)

 

Boiled soya beans

The dry soya beans were weighed out daily and boiled each morning for half an hour in order to destroy the antinutritional factors in the grain. After boiling the grain was put into a bamboo basket to drain and cool before feeding.

Boiled soya beans were offered twice a day, in the morning and afternoon, in amounts according to the treatment and according to liveweight. Daily amounts of whole boiled soya beans started at 12.5 g crude protein/day at 1.0 kg body weight, increasing weekly to a maximum of 25 g crude protein/day at 2.0 kg. The weight of soya beans offered was adjusted every week according to the mean pen live weight for that week.

Azolla

Azolla was harvested each afternoon during the experimental period and was put into a bamboo basket for one hour before feeding in order to drain the excess water from the plant. The fresh Azolla was offered ad libitum three, four or five times per day, at a rate of 1 kg fresh weight per pen at each feeding. The times increased with the age of the birds to minimize losses. Refusals were collected and weighed the following morning.

Sugar cane juice

Due to technical problems concerned with the purchase and storage of sugar cane, reconstituted raw sugar solutions were used. Raw sugar was dissolved in cold water in a proportion of 2.2 kg raw sugar to 5 kg water, approximately, and then was mixed and measured as Bohmer degrees, to give a value of 11 Bohmer, equal to 20°Brix (total dissolved sugars). This was offered to the ducks in plastic basins covered with a grille to ensure that there was minimum spillage of the juice. The reconstituted sugar cane juice was offered ad libitum three, four or five times per day, with 800 ml/pen in each feeding, the times increasing with the age of the ducks to ensure that there was minimum loss. Juice remaining in the basins each morning was collected and weighed to calculate amounts consumed.

Chemical analysis

Sample preparation and analyses of the dietary ingredients for dry matter (DM), crude protein (CP), crude fibre (CF), ether extract (EE), ash, calcium, phosphorus and carotene were carried out at Cantho University using standard procedures.

Carcass measurements

At the end of the experiment, the ducks were weighed individually and two ducks per pen (one male and one female) were selected at random for carcass analysis. The birds were slaughtered at 72 days of age, eviscerated and plucked, and the carcass weight recorded.

Statistical analysis

The data were analysed by analysis of variance using the GLM (General Linear Model) procedure of MINITAB version 8.2 program statistical software (Minitab Inc., 3081 Enterprise drive, State College, PA, 1680-3008, 1991, USA). The balanced design of the trial permitted the use of GLM with initial live weight as a covariate. A similar method was used to analyse the carcass traits.

Economic analysis

An economic analysis was carried out to compare the cost and profitability of the dietary treatments.

Results

Trial 1: azolla replacing soya beans, with daily protein supply increasing with liveweight

Feed composition

The chemical composition data of the whole boiled soya beans, Azolla and sugar cane juice are shown in Table 2. The Azolla had a mean dry matter content of 5.6%, crude protein 26.7%, crude fibre 11%, ether extract 4.6%, Ca 0.8% and total P 0.4% (DM basis).

Table 2: Chemical composition of the whole boiled soya beans, Azolla and sugar cane juice
BLGIF.GIF (44 bytes)
Analysed composition Sugar cane juice
Soya Beans Azolla
BLGIF.GIF (44 bytes)
Dry matter 91.8 5.6 20.0
As % of DM
N x 6.25 38.8 26.7 1
Crude fiber 8.4 11.2 --
Ether extract 20.0 4.6 --
Ash 5.1 15.1 --
Ca 0.4 0.8 --
P (total) 0.5 0.4 --
Carotene (mg/kg) -- 326 --
BLGIF.GIF (44 bytes)

 

The raw sugar used in the experiment was collected from a small sugar refining factory in the area, and is the syrup resulting from the evaporation of sugar cane juice. The sample used in this experiment had the following chemical composition: (% as received basis): ?Brix 70; dry matter 70%; crude protein 1 %; ash 4.9%; sucrose 58.1%; reducing sugars (as glucose) 8.5%.

Feed intake, growth and conversion

Total dry matter intake was increased by Azolla when offer level of soya bean protein was only slightly less than on the control diet (diet Az15). With increased restriction of soya bean, dry matter intake decreased linearly (r= 0.81) according to protein consumed as soya bean (Table 3).

Table 3: Effect of replacing boiled soya beans with Azolla in sugar cane juice based diets on feed intake and performance of growing ducks (Trial 1).
BLGIF.GIF (44 bytes)
Item Ctl Az15 Az30 Az45 Az60 SE/Prob
BLGIF.GIF (44 bytes)
No birds 40 40 40 40 40
Liveweight, g
Initial 717 735 698 741 697
Final 1861 1940 1828 1706 1564
Daily gain 28.6 30.4 28.3 24.1 21.4 ±0.63/0.01
Feed intake, g/d
Soya bean 55.7 52.8 42.7 34.2 25.4
Azolla -- 233 234 279 301 ±4.48/0.01
Cane juice 400 442 422 433 426 ±8.89/0.05
Total DM 131 149 136 134 127 ±1.9/0.001
Total CP 20.6 23.0 19.5 17.2 14.5 ±0.15/0.01
CP from Azolla:
g/day -- 3.5 3.5 4.2 4.4 ±0.06/0.01
% of total CP -- 15.2 17.9 24.4 30.3
Feed conversion,
kg DM/kg gain 4.59 4.86 4.77 5.57 5.95 ±0.18/0.01
BLGIF.GIF (44 bytes)

 

The decrease in total dry matter intake appeared to be caused by the inability of the ducks to eat more azolla when soya bean was restricted beyond 73% of the control level. Intakes of Azolla were lower than expected, increasing from a mean of 233 g/day on the Az15 diet to only 301 g/day on the Az60 diet. The proportion of the crude protein intake supplied by Azolla was only 15.2, 17.9, 24.4, and 30.3% of the total, for diets Az15, Az30, Az45 and Az60, respectively. But more significant was the decrease in total protein intake which fell from 23 g/day on diet Az15 to only 14.5 g/day on diet Az60. As there is no evidence of palatability problems with Azolla it is possible that the bulky nature of the plant was the reason for the lower than expected intakes. Mean intakes of cane juice were 400, 442, 421, 432, and 426 ml/day for the control, Az15, Az30, Az45 and Az60 treatments, respectively.

Growth rate was linearly related to protein intake both total and that derived from the soya beans; however, the correlation was stronger with total protein (r=0.98) compared with soya bean protein (r=0.93). When soya bean protein was restricted to up to 73% of that in the control diet the ducks compensated by eating azolla to achieve higher (treatment Az15) or the same total intake of protein (Az30). However, when soya bean intakes were restricted to less than 60% of the control level, the ducks were not able to eat enough azolla to compensate for the deficiency in protein and growth rate fell. Thus it can be concluded that azolla can effectively replace up to 17% of the normal level of soya bean protein with no reduction in grrowth, and that low levels of Azolla in addition to the normal level of soya bean actually stimulate growth (Treatment Az15). In contrast with the results for growth, feed conversion ratios deteriorated with offer level of Azolla and were related directly and negatively with soya bean protein level (r= -0.94).

Carcass parameters

Carcass parameters (Table 4) were not affected by dietary treatment (P>0.05).

Table 4: Effects of replacing whole soya bean with Azolla in diets on carcass parameters of ducks (Trial 1).
BLGIF.GIF (44 bytes)
Item Control Az15 Az30 Az45 Az60 SE/prob
BLGIF.GIF (44 bytes)
Liveweight, g 1911 1915 1845 1737 1608
Carcass
Weight, g 1384 1268 1324 1253 1117 ±70/0.65
Yield, % LW 72 67 72 72 69 ±2.7/0.79
Heart, g 11.6 13.6 12.3 13.7 13.5 ±1.4/0.317
Liver, g 44.6 48.2 45.4 48.6 48.3 ±3.2/0.99
Gizzard, g 51.9 51.3 50.8 44.7 44.7 ±3.5/0.44
Breast, g 278 276 271 264 251 ±18.1/0.71
Breast
muscle, g 172 168 156 151 131 ±15.2/0.66
Breast fat+
skin, g 51.2 58.0 58.5 58.0 62.3 ±6.8/0.56
Breast
bone, g 49.5 51.7 56.2 58.3 47.7 ±4.5/0.24
Carcass
measurements, cm
Length 22.7 22.3 22.6 23.4 22.2 ±0.6/0.232
Small int. length 205 191 214 204 210 ±8.86/0.99
Large int. length 12.0 11.4 12.9 12.0 12.6 ±0.77/0.39
BLGIF.GIF (44 bytes)

 

Economic analysis

Optimum economic results (Table 5) were obtained with an offer level of protein of 23 g/day made up of 73% from boiled soya beans and 17% from Azolla.

Table 5: Economic analysis of replacing soyabeans with Azolla, Vietnamese Dong (1US$ = 10.500 VND) (Trial 1).
BLGIF.GIF (44 bytes)
Item Control Az15 Az30 Az45 Az60
BLGIF.GIF (44 bytes)
Daily intakes, g
Soya bean 55.7 52.8 42.7 34.2 25.4
Fresh Azolla -- 233 234 279 301
Cane juice 400 442 422 433 426
Premix, salt 0.20 0.20 0.16 0.12 0.09
Costs of the diet/day:
Boiled soybean 184 174 141 113 83.8
Fresh Azolla 23.3 23.4 27.9 30.1
Cane juice 72.4 80.5 76.3 78.3 77.1
Premix, salt 3.8 3.6 2.9 2.3 1.7
Total cost, VND
Per day 260 2826 244 221 193
Trial period 10400 11264 9740 8852 7708
Cost of feed/ kg
gain 9091 9345 8619 9173 8890
Profit/bird -104.9 -417 433 -167 95
BLGIF.GIF (44 bytes)

 

Trial 2: azolla replacing soya beans with daily protein allowances fixed

Materials and methods

In the first trial the protein supply was adjusted weekly and increased with the age and liveweight of the ducks. In this trial the daily amounts of boiled soya beans offered were the same throughout the experiment and the proportions of crude protein contributed by Azolla were correspondingly lower than in trial 1. This is the system used by small scale farmers in Vietnam.

The experimental design, housing, feeding and management procedures were identical to those followed in trial 1.

The experiment was carried out between April and June, 1993. A total of 200 F1 Cherry Valley hybrids with initial average live weight between 900 and 970 g were used. The ducklings were fed a commercial type starter diet between 1 and 28 days of age, and then were allocated at random to one of the experimental diets. The initial total body weight of the ducks in each treatment was approximately the same. The birds were identified and individually weighed at the beginning (28 days) and also at slaughter. Group weights were taken once per week throughout the experiment. The experimental period was preceded by a preliminary period of one week. The ducks were group fed with different amounts of soya bean and had free access to Azolla. All the ducks were offered reconstituted sugar cane juice ad libitum as the main source of energy.

Total crude protein requirements were estimated from NRC recommendations (NRC 1984) and pilot trials to determine feed intakes for increasing liveweights. Daily boiled soya bean allowances were restricted to provide 100, 85, 75, 65 and 55% of the recommended levels of protein. A vitamin-mineral premix (0.5% of the diet) and common salt (0.25% of the diet) were mixed with the whole boiled soya bean only for the control group. Details of the feeding regime are in Table 6.

Table 6: Proportions of ingredients (dry matter basis) in the diets of fattening ducks (28-60 days) (Trial 2)
BLGIF.GIF (44 bytes)

Protein from

Soya Azolla Cane juice
BLGIF.GIF (44 bytes)
Control 100 -- ad lib.
Az15 85 ad lib. ad lib.
Az25 75 ad lib. ad lib.
Az35 65 ad lib. a d lib.
Az45 55 ad lib. ad lib.
BLGIF.GIF (44 bytes)

Results and discussion

The chemical composition of the whole boiled soya beans was the same as in Trial 1 (Table 1). The raw syrup used in this experiment had the following chemical composition (% as received basis): ?Brix 72.3; dry matter 72%; crude protein 1 %; ash 4.5%; sucrose 56.2%; reducing sugars (as glucose) 13%.

As in Trial 1, intakes of Azolla were lower than expected, increasing from 257 g/day on the Az15 diet to only 284 g/day on the Az45 diet. Total protein intake thus decreased from 25.5 and 25.9 on control and Az15 diets to 18.6 g/day on the Az45 diet. As in Trial 1, growth rate was better correlated with total protein intake (r=0.97) than with intake of soya bean protein (r=0.94) indicating a benefit from the Azolla supplementation at the low level of substitution (Table 7).

Table 7: Effect of replacing boiled soybeans with Azolla in sugar cane juice based diets on feed intake and performance of growing ducks (Trial 2).
BLGIF.GIF (44 bytes)
Item Control Az15 Az25 Az35 Az45 SE/prob
BLGIF.GIF (44 bytes)
Liveweight, g
Initial 966 910 924 943 919
Final 2046 1951 1918 1873 1710
Daily gain 32.6 31.5 30.2 28.2 24.1 ±1.1/0.001
Feed intake, g/day
Soya bean 70.0 60.0 52.5 45.5 38.5
Azolla -- 257 274 268 284 ±4.45/0.01
Cane juice 279 342 347 340 338 ±3.35/0.01
Total DM 120 137 133 125 119 ±0.72/0.01
Total CP 25.5 25.9 23.4 20.8 18.6 ±0.06/0.01
CP as Azolla,% -- 14.7 17.5 19.2 22.6
Feed conversion,
kg DM/kg gain 3.7 4.3 4.4 4.4 4.9 ±0.16/0.01
BLGIF.GIF (44 bytes)

 

A supplementary source of vitamins and minerals was not included in the diets of the groups that received Azolla and yet there were no obvious health problems or deficiency symptoms indicating that the Azolla was supplying these essential nutrients. This apparent capacity of Azolla to supply vitamins and minerals is an important advantage in rural areas where premixes may not be available or are expensive. However, it should be mentioned that the ducks were given commercial starter diets, which contained vitamins and minerals, up to one month of age, and some of these would have been stored in the body.

There were no effects of treatment on carcass characteristics (Table 8).

Table 8: Effects of replacing whole soybeans with Azolla in the diets of fattening ducks on carcass parameters (Trial 2).
BLGIF.GIF (44 bytes)
Item Control Az15 Az25 Az35 Az45 SE/prob
BLGIF.GIF (44 bytes)
Liveweight, g 1901 1786 1768 1858 1641
Carcass Weight, g 1339 1287 1262 1326 1179 ±73.7/0.54
Yield, % LW 70 72 71 71 72 ±1.6/0.33
Heart, g 11.4 12.8 10.8 12.5 9.9 ±1.0/0.15
Liver, g 43.6 40.2 37.4 40.9 37.6 ±3.3/0.39
Gizzard, g 55.4 53.7 53.2 53.5 48.7 ±4.9/0.65
Breast weight, g 273 251 254 251 232 ±20.8/0.06
Breast muscle, g 170 143 148 149 137 ±15.6/0.23
Breast fat+ skin, g 48.3 55.3 57.1 49.5 39.1 ±8.16/0.26
Breast bone, g 41.7 46.6 45.3 48.5 51.0 ±5.56/0.20
Carcass
measurements, cm
Length 22.6 22.6 23.0 24.4 22.5 ±0.72/0.75
Small int. length 204 196 202 217 207 ±7.66/0.56
Large int length 12.9 13.2 12.6 13.5 11.3 ±0.71/0.70
BLGIF.GIF (44 bytes)

 

The deeper yellow color of the legs, beaks and skin of the ducks fed with Azolla compared to the control group was noted and substantiated the observations made in Trial 1.

The economic analysis is presented in Table 9. Daily feed costs were less with the lower levels of soya bean but the reduction in rate of gain on these diets cancelled out this advantage.

Table 9: Economic analysis (VND) of replacing soyabeans with Azolla in the diet of fatteningducks (1US$ = 10,500 VND)
BLGIF.GIF (44 bytes)
Item Control Az15 Az25 Az35 Az45
BLGIF.GIF (44 bytes)
Daily intakes, g
Soya bean 70.0 60.0 52.5 45.5 38.5
Fresh Azolla - 257 2749 268 284
Cane juice 279 342 347 340 338
Premix, salt 0.26 - - - -
Cost of the diet
(VND/day):
Soya bean 231 198 173 150 127
Fresh Azolla 25.7 27.4 26.7 28.3
Cane juice 50.5 61.9 62.7 61.6 61.2
Premix, salt 4.8 - - - -
Total cost (VND)
Per day 286 286 263 239 217
Trial period 9448 9425 8693 7871 7149
Cost feed/kg gain 8755 9057 8743 8459 9023
Profit/bird 265 -58.8 256 503 -18.0
BLGIF.GIF (44 bytes)

 

Discussion

A low digestibility of the protein in Azolla could be one explanation of the poorer growth rates when a high level of substitution of soya beans was attempted. However, in a digestibility trial with broiler chicken, Alcantara and Querubin (1985) concluded that nutrient digestibilities of crude protein, crude fat, and crude fibre were not affected by the level of Azolla in the ration, and that broilers can readily digest the crude fibre in Azolla, but not that in rice bran, so that digestibility may not have been a limiting factor.

The other important characteristic of a feed protein for ducks is its balance of essential amino acids. These were not analyzed in either of the trials but all indications from the literature are that most strains of Azolla strains have a well balanced array of essential amino acids and constitute high quality protein if cultivated in good conditions (Van Hove 1989).

There are few references to feeding trials that have been carried out with Azolla for poultry. In an experiment in India, White Leghorn females were fed a commercial poultry feed and fresh Azolla at levels of 5, 12.5, or 16% on a dry matter basis. The birds receiving the diet with 5% Azolla grew faster than the control group and those given the diet with 12.5% Azolla grew only slightly slower, although at 16% inclusion growth rates were significantly reduced (Singh and Subudhi 1978).

A series of feeding trials was conducted by Escobin (1987) to determine the effects of feeding fresh Azolla as partial replacement to traditional paddy rice-snail-shrimp (PSS) based rations for laying Mallard and growing Muscovy ducks. In terms of production efficiency, the results showed no significant differences between the dietary treatments containing 0, 20, 30 and 40% Azolla replacing corresponding levels of PSS, both for Mallard (egg production) and Muscovy (meat production) ducks.

Conclusion

From the results of these trials it can be concluded that fresh Azolla can partially replace whole soya beans up to a level of about 20% of the total crude protein in diets of fattening ducks based on sugar cane juice, without any problems and with no adverse effects on growth rate, or health. Cost of feed per kg gain was lowest, and net profit per bird highest for this treatment. However, at levels of replacement above this, rates of gain and feed conversion efficiency were significantly poorer.

Acknowledgements

Grateful acknowledgement is made to the Swedish International Development Authority (SIDA) for the financial and material support of this project. Facilities for the experiments were provided by the University of Cantho through the cooperation of Mr Bui Xuan Men and help was received from Ms Kim Dong and Mr Sanh in field work and from Ms Xuan Dung in the laboratory.

References

Alcantara P F and Querubin L J 1985 Feeding value of Azolla meal for broilers. Philippine Journal of Veterinary and Animal Sciences 11:1-8.

Cassani J R 1981 Feeding behavior of under yearling hybrids of grass carp Ctenopharyngadon idella female and the bighead Hypophthalmichtys nobilis male on selected species of aquatic plants. Journal of Fish Biology 18(2):127-138.

Escobin R P Jr 1987 Fresh Azolla (Azolla microphylla kaulfuss) as partial replacement to palay-snail-shrimp based rations for laying mallard and growing-fattening muscovy ducks. College Laguna 71.

Lumpkin T A and Plucknet T L 1982 Azolla as a green manure: use and management in crop production. Westview Press Boulder, Colorado. Westview Tropical Agriculture, Series #15, 230p.

Lumpkin T A 1984 Assessing the potential for Azolla use in the humid tropics. International Rice Reseach, Communication Newslettter 10.

Moore A W 1969 Azolla: Biology and agronomic significance. Botanical Reviews 35: 17-35.

NRC 1984 Nutrient requirements of poultry. 8th edition. National Academy of Sciences, Washington, DC.

Pullin R SV and Almazan G 1983 Azolla as fish food. ICLARM Newsletter 1:6-7.

Querubin L J, Alcantara P F and Princesa A O 1986 Chemical composition of three Azolla species (A. caroliniana, A.microphylla and A. pinnata) and feeding value of Azolla meal (A. microphylla) in broiler rations II. Philippine Agriculture 69:479-490.

Reynaud P A and Franche 1987 Azolla pinnata var. africana. De la biologie moleculaire aux applications agronomiques. ORSTOM edition 1-15.

Singh P K and Subhudhi B P R 1978 Utilize Azolla in poultry feed. Indian Farming 27:37-38.

Subhudhi B P R and Singh P K 1978 Nutritive value of the water fern Azolla pinnata for chicks. Poultry Sci 57:378-380.

Van Hove C and López Y 1983 Fisiología de Azolla. In : Boletín técnico, Universidad Nacional de Colombia, Facultad de Ciencias Agropecuarias, Palmira. Volumen 1, Number 1. p 43-58.

Van Hove C 1989 Azolla and its multiple uses with emphasis on Africa. FAO, Rome 53pp

Vo Minh Kha and Tran Quang Thuyet., 1970. Beo Hoa Dau (Azolla). Nha Xuat Bang Nong Thon, Hanoi (Vietnamese). 174 pp.

(Received 1 June 1995)