Seven samples from six aquatic plant
species available in the Ecological Farm of UTA, Chamcar Daung, Cambodia, were selected
for a screening test to evaluate in vitro pepsin/pancreatin
digestibility of N and to explore the possible relationships with other non conventional
tests for assessing their nutritive value for pigs. The samples were the aerial part of
water hyacinth (Eichhornia crassipes) and water spinach (Ipomoea aquatica), and the entire plants from water
lettuce (Pistia stratiotes), azolla (Azolla pinnata), duckweed (Lemna minor) and spirodella (Spirodella polyrhyza). The duckweed was analysed
fresh or after sun-drying.
Dry matter (DM) values were from 6.3 to 91.1%; nitrogen (N) and neutral detergent fibre (NDF)
concentrations (dry basis) were from 2.31 to
5.54 % and 29.7 to 58.1%, respectively. Water solubility of N and in vitro digestibility of N were high and within a
relatively narrow range (N solubility, 59.3 to 81.5%; in vitro, pepsin/pancreatin N digestibility, 50.5
to 76.6%). In vitro N digestibility was
positively associated with water soluble N (r=0.74), water soluble DM (r =0.71) and in vitro DM digestibility (r=0.75) but not with
NDF-linked N (r = -0.043). In vitro N digestibility was highest for azolla and
fresh duckweed (76.6 and 75.4% respectively) and lowest for water hyacinth (50.5%). Water soluble DM (r = 0.74) was a better predictor
of in vitro DM digestibility than NDF (r =
-0.48).
The results of this
study show that water soluble N is a useful indicator of the digestibility for pigs of the
protein in water plants.
Aquatic plants, either floating macrophytes or
amphibious species, are in current use in several tropical countries of
In contrast with the accumulating experimental
evidence from
The experiments reported in this communication aimed to assess the nutritive value for pigs of the protein in a range of water plants and to test the relationships between the simple water soluble N method (Ly and Preston 2001; Ly et al 2001a,b)) and the in vitro pepsin-pancreatin N digestibility technique which has been shown to be highly correlated with in vivo ileal digestibility of protein in pigs (Dierick et al 1985).
Six tropical aquatic plants were selected for
the study (Table 1). The samples were obtained from plants that were: harvested
periodically at the UTA Ecological Farm on the
campus of the Royal University of Agriculture, Chamcar Daung; were purchased in the local
market; or were collected from a lake close to
the University Campus. The samples were the aerial part of water hyacinth (Eichhornia crassipes) and water spinach (Ipomoea aquatica), and the entire plant from water
lettuce (Pistia stratiotes), azolla (Azolla pinnata), duckweed (Lemna minor) and spirodella (Spirodella polyrhyza). The duckweed was analysed
fresh or after sun-drying. Analysis for water solubility of DM and N was as described by
Ly and
Table 1.
Identification and origin of the water plants |
||||
Common
name |
||||
Scientific name |
Origin |
English |
Spanish# |
Khmer |
Azolla pinnata |
Wild in lake## |
Azolla |
Azolla |
- |
Eichhornia crassipes |
Wild in lake |
Water hyacinth |
Jacinto de agua |
Kamplauk |
Ipomoea aquatica |
Local market |
Water spinach |
Espinaca acuática |
Trocoum |
Lemna minor |
Cultivated in UTA |
Duckweed |
Lemna |
Chauk |
Pistia stratiotes |
Wild in lake |
Water lettuce |
Lechuga de agua |
Chauk |
Spirodella
polyrhiza |
Wild in lake |
Duckweed |
Chauk |
|
# Cuban Spanish ##
Cheung Ek lake at the |
Mean values for DM ranged
from 6.3 to 91.1%, and for N and NDF (dry basis) from 2.31 to 5.54 % and from 29.7 to
58.1%, respectively (Table 2). The selected materials were characterized by a low DM
content, with the exception of the sun-dried duckweed,
and a relatively high concentration of N. The aerial part of water hyacinth was much lower
in crude protein (14.0% in DM) than the other water plants (range of 22 to 34% in DM). .
Table
2. Content of dry matter (DM), organic matter ( |
||||
Scientific name |
DM |
NDF |
N |
|
Azolla pinnata
|
6.80 |
82.9 |
42.8 |
4.50 |
Eichhornia crassipes |
14.6 |
86.7 |
55.0 |
2.31 |
Ipomoea aquatica |
17.8 |
92.2 |
29.7 |
3.49 |
Lemna
minor (fresh) |
6.34 |
88.0 |
40.3 |
4.03 |
Lemna
minor (sun dried) |
91.1 |
89.0 |
41.9 |
4.74 |
Pistia
stratiotes |
6.85 |
78.6 |
47.3 |
5.54 |
Spirodella
polyrhiza |
4.71 |
90.5 |
58.2 |
4.57 |
In vitro, pepsin/pancreatin digestibility of DM and N was assayed in dried, re-ground samples in quadruplicate according to the procedure outlined by Dierick et al (1985). Incubations of every leaf sample were conducted in quadruplicate and subsequent analyses were the same as used for determination of the chemical composition of the samples.
Pearson correlation
coefficients and other basic statistical approaches were according to standard biometrical analyses (Steel and Torrie
1980), using Minitab software (Ryan et al
1985).
In vitro
digestibility and water solubility of N was particularly high in the samples of azolla and
duckweed, whereas this index was low for water hyacinth (Table 3). Water lettuce and
spirodella showed the lowest water solubility of DM, while in vitro digestibility of DM was lowest in water
hyacinth.
Table 3. Water solubility and in vitro digestibility (%), of DM and N, of
several tropical aquatic plants |
||||
Scientific name |
WSDM |
IVDDM |
WSN |
IVDN |
Azolla pinnata |
59.7 |
52.2 |
73.6 |
76.6 |
Eichhornia crassipes |
45.3 |
33.3 |
59.3 |
50.5 |
Ipomoea aquatica |
45.4 |
42.1 |
64.3 |
54.6 |
Lemna minor (fresh) |
70.0 |
51.2 |
73.7 |
75.4 |
Lemna minor (sun
dried) |
56.8 |
56.4 |
65.5 |
62.2 |
Pistia stratiotes |
31.4 |
40.0 |
81.5 |
62.2 |
Spirodella polyrhiza |
40.8 |
40.0 |
68.1 |
54.2 |
WSDM, IVDDM, WSN and IVDN are water solubility of DM, in vitro
digestibility of DM, water solubility of N and in vitro digestibility of N, respectively. |
The high values for in vitro digestibility and water solubility of N in
duckweed and azolla are in accordance with reports from
Table
4. Pearson correlation coefficients for non-conventional indices of nutritive value
from several aquatic plants |
|||||||
DM |
N |
NDF |
NDFN |
WSDM |
IVDMD |
WSN |
|
N
|
0.75 |
||||||
NDF
|
-0.74 |
-0.029 |
|||||
NDFN |
-0.48 |
-0.29 |
0.69 |
||||
WSDM |
0.058 |
-0.16 |
-0.37 |
0.18 |
|||
IVDDM |
0.16 |
0.44 |
-0.48 |
-0.019 |
0.74 |
||
WSN |
-0.29 |
0.81 |
-0.073 |
-0.38 |
-0.073 |
0.25 |
|
IVDN |
-0.17 |
0.42 |
-0.34 |
-0.043 |
0.70 |
0.75 |
0.62 |
DM, N. NDF, NDFN, WSDM, IVDDM, WSN and IVDN are dry matter,
nitrogen, neutral detergent fibre, neutral detergent fibre-linked N, water solubility of
DM, in vitro digestibility of DM, water solubility of N and in vitro digestibility of N,
respectively. |
The
results of the present investigation show the same trend found in previous studies (Ly and
Preston 2001; Ly et al 2001b) where water soluble N was correlated to in vitro, pepsin/pancreatin digestibility of the N
fraction of cell wall materials. Studies with conventional feeds for pigs have shown that in vitro digestibility of N can predict in vivo, ileal digestibility of N (Dierick et al
1985; Boisen and Fernandez 1995; Pujol et al 2001; Swiech and Buraczewska 2001). A similar
conclusion can be drawn for non-conventional diets of aquatic floating macrophytes (Table
5).
Table 5. In vivo and in vitro digestibility of several aquatic plants |
|||||||
Azolla pinnata |
Lemna minor |
Ipomoea aquatica |
Eicchornia crassipes |
|
|||
In vivo digestibility, % |
|||||||
N |
64.6 |
56.0 |
- |
16.2 |
Dominguez et al (1997) |
||
In vitro digestibility, % |
|||||||
Dry matter |
52.2 |
51.2 |
42.1 |
33.3 |
This experiment |
||
N |
70.1 |
67.4 |
- |
41.2 |
Dominguez et al (1997) |
||
N |
65.0 |
69.0 |
68.0 |
Ly and |
|||
N |
76.6 |
75.4 |
54.6 |
50.5 |
This experiment |
||
In vivo digestibility refers to ileal digestibility as
measured in pigs and estimated by difference (Dominguez et al 1997). In vitro
digestibility refers to pepsin/pancreatin solubility resembling in vivo ileal
digestibility (Ly and Preston 2001; this experiment) |
|||||||
The results of the experiment described in this communication
demonstrate that non-conventional evaluations of cell wall rich materials as potential
protein sources for pigs are viable
alternative options that can be readily applied in many tropical countries. Further
research is needed to improve the accuracy of measurements relating to water solubility
and N digestibility of tropical foliage feeds and also to find theoretical support for the
present results.
This publication is
an output from a collaborative research project funded by FAO,
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Received 17 October 2001