Effect of position in the tree and pretreatment of Acacia mangium
leaves on rumen dry matter and nitrogen degradabilities
An Xuan Bui, Hieu Trong Luu,
Khang Nguyen Duong and T R Preston*
University of Agriculture and Forestry, Ho
Chi Minh City, Vietnam
*SAREC Adviser (Centro para la
Investigación en Sistemas Sostenibles de Producción
Agropecuaria [CIPAV], Cali AA20591, Colombia)
Summary
The hypotheses were that the relative rate of degradability of
Acacia mangium leaves in the rumen would be low; and that
this could be improved by chemical pretreatment with acid or
alkali. In trial 1, using a 3 x 2 factorial design with three
replications (fistulated steers), the main treatments were leaves
taken from the bottom (B), the middle (M) or the top (T) branches
of Acacia mangium trees; the sub-treatments were
the absence (-MUB) or presence (+MUB) of a molasses-urea block in
the diet of the animals used for the incubations.
The degradability of both dry matter and nitrogen decreased
significantly (r5=.85, P=.001; and r5=.50, P=.03 for -MUB: and
r5=.96, P=.001; and .29; P=.13 for +MUB respectively) as the
position of the leaves in the tree changed from top to bottom.
Overall means for DM were: 27.5, 25.6 and 22.7% in 48hr and for
N, 20.5, 18.5 and 16.4% for top, middle and bottom leaves.
Degradabilities of DM were significantly higher (P=.001) in
steers receiving the MUB (27.6%) than in those fed only rice
straw (22.9); comparable values for N were: 20.2 and 16.7
(P=.01). Values for degradability were in general low (maximum of
30% for dry matter and 22% for N) considering the incubation
period in the rumen was 48h.
In trial 2, in a factorial design 10 x 2 with 3 replications
(animals), the main variables were chemical pre-treatment of the
leaves of Acacia mangium as follows: Control (no
treatment), NaOH solutions of 2%, 3%, 6%, 9% (w/v) in which the
leaves were soaked for 48h, urea solutions of 3%, 6%, 9% (w/v)
added at the rate of 300 ml/1 kg of fresh leaves and ensiled for
7 days, Ca(OH) 2 solution of 10% (w/v) in which the
leaves were soaked for 48h; "A" molasses diluted in
water (1 part molasses: 2 parts water v/v) fermented in open
vessels for 7 days then added to the leaves (1.5 litres fermented
solution/10 kg fresh leaves) and ensiled for 7 days. The
sub-treatments were the presence (+MUB) or absence (-MUB) of the
molasses-urea block as supplement to the basal diet of rice straw
that was fed to the fistulated steers.
The leaves were collected from the mid-point of 2-year-old Acacia
mangium trees and were cut into 3 cm strips prior to being
treated with the different additives.
All the chemical pre-treatments increased the degradability of
both dry matter and nitrogen compared with the control (P=.001).
The rumen degradabilities were higher in the steers having access
to the molasses-urea blocks. The highest dry matter degradability
was with the fermented molasses treatment (45%) which was
superior by 62% compared with the control (27.8%) for the +MUB
treatment and by 58% for -MUB (values of 37.1 and 23.5
respectively). Corresponding improvements for N degradability
were even higher at 89 and 103%, respectively. There were linear
increases in degradability of both dry matter and N as the
concentration of NaOH, or urea, increased in the treatment media.
The experimental findings support the hypotheses that the
rumen degradability of leaves of Acacia mangium is low and
that this can be improved markedly by chemical pre-treatment,
especially Ca(OH)2 and acetic acid (the main product
of the fermentation of molasses).
KEY WORDS: Forage trees, Acacia mangium, position of
leaves, rumen in sacco degradability, chemical pre-treatment, dry
matter, nitrogen, secondary plant compounds.
Introduction
The legume tree Acacia mangium has important qualities
as a multi- purpose tree in the tropics as it is high yielding,
produces good timber and is tolerant of low moisture conditions
and aluminium- saturated acid soils (Ngo and Nguyen 1991). There
appear to be no reports of the nutritive value for livestock of
the foliage, other than observations that its palatability is low
(An Xuan Bui, unpublished data).
The hypotheses that were tested in the research described were
that (i) the relative rate of degradability of Acacia mangium
leaves in the rumen would be low; and (ii) that this could be
improved by chemical pretreatment with acid or alkali.
Experiment 1
TREATMENTS AND DESIGN: There were 6 treatments arranged in a 3
x 2 factorial design with three replications. The main treatments
were leaves taken from the bottom (B), the middle (M) or the top
(T) branches of Acacia mangium trees; the sub-treatments
were the absence (-MUB) or presence (+MUB) of a molasses-urea
block in the diet of the animals used for the incubations; the
replications were three rumen-fistulated animals.
MATERIALS, ANIMALS AND MEASUREMENTS: The leaves were collected
from a stand of 2 year-old trees of Acacia mangium, dried
at 60 degrees C and ground through a 1mm sieve. The basal diet
(-MUB) of the fistulated steers (crossbreed Sindhi x Vietnamese)
was dry rice straw fed at a level 30% above measured intake; the
experimental diet consisted of supplementation of the rice straw
with a molasses-urea block (+MUB). The MUB contained (% fresh
basis) 35 "A" molasses, 10 urea, 40 rice bran, 5 salt
and 10 quicklime.
The ground leaves were put in nylon bags (2 per treatment in
each animal) and incubated for 48h in the rumen of the fistulated
steers when they were withdrawn, washed, dried and weighed
(Orskov et al 1980). Samples of the original dried ground leaves
and of the residues in the bags were analyzed for nitrogen
(macro-kjeldahl method).
Results and discussion
The results are presented in table 1.
| Table 1: Mean values
for 48h degradability of dry matter and of nitrogen of
samples of Acacia mangium leaves incubated in the
rumens of steers fed rice straw with and without access
to molasses-urea blocks (MUB) |
 |
| |
Position
of leaves in the tree |
|
| |
Top |
Middle |
Bottom |
Means SEM(P=) |
|
| DegradabilityDM
|
(% 48hr) |
|
|
|
| -MUM |
25 |
23.4 |
20.4 |
22.9 |
| +MUB |
30 |
27 |
25 |
27.6 ±.23
(.001) |
| Means |
27.5 |
25.6 |
22.7 |
|
| SEM (P=) |
|
"0.29
(.001) |
|
|
| |
|
|
|
|
| DegradabilityN
|
(% 48hr) |
|
|
|
| -MUB |
19 |
17 |
14.2 |
16.7 |
| +MUB |
22 |
20 |
18.7 |
20.2
".83 (.01) |
| Mean values |
20.5 |
18.5 |
16.4 |
|
| SEM (P=) |
|
±1.02 (.05) |
|
|
|
SEM=Standard error of mean
The degradability of both dry matter and nitrogen decreased
significantly (r5=.85 and .50; P=.001 and .03 for -MUB and r5=.96
and .29; P=.001 and .13 for +MUB respectively) as the position of
the leaves in the tree changed from top to bottom.
Degradabilities were significantly higher in steers receiving the
MUB than in those fed only rice straw (P=.001 and .01 for Dm and
N respectively). Values for degradability were in general low
(maximum of 30% for dry matter and 22% for N) considering the
incubation period in the rumen was 48h.
Experiment 2
TREATMENTS AND DESIGN: There were 20 treatments arranged in a
factorial design 10 x 2 with 3 replications (animals). The main
variables were chemical pre-treatment of the leaves of Acacia
mangium as follows:
# Control (no treatment)
# NaOH solutions of 2%, 3%, 6%, 9% (w/v) in which the leaves
were soaked for 48h
# Urea solutions of 3%, 6%, 9% (w/v) added at the rate of 300
ml/1 kg of fresh leaves and ensiled for 7 days
# Ca(OH)2 solution of 10% (w/v) in which the leaves
were soaked for 48h
# "A" molasses diluted in water (1 part molasses: 2
parts water v/v) fermented in open vessels for 7 days then added
to the leaves (1.5 litres fermented solution/10 kg fresh leaves)
and ensiled for 7 days
The sub-treatments were the presence (+MUB) or absence (-MUB)
of the molasses-urea block as supplement to the basal diet of
rice straw that was fed to the fistulated steers.
MATERIALS, ANIMALS AND MEASUREMENTS: The leaves were collected
from the mid-point of 2-year-old Acacia mangium
trees and were cut into 3 cm strips prior to being treated with
the different additives. 2 kg of leaves were processed for each
treatment. The fistulated steers and the procedures for
determining rumen degradabilities of dry matter and nitrogen were
the same as in Experiment 1.
| Table 2: Effect
of pre-treatment of Acacia mangium leaves and of
supplementing with molasses-urea block the host
(incubator) animal on rumen degradability of leaf dry
matter |
|
| |
-MUB |
+MUB |
Means |
|
| Control |
23.5 |
27.8 |
25.6 |
| 2% NaOH |
26.6 |
30.1 |
28.3 |
| 3% NaOH |
27 |
31.7 |
29.3 |
| 6% NaOH |
27.6 |
24.7 |
31.1 |
| 9% NaOH |
28.2 |
36.2 |
32.2 |
| 3% Urea |
29.2 |
37.0 |
33.1 |
| 6% Urea |
32.2 |
39.2 |
35.7 |
| 9% Urea |
33.6 |
41.2 |
37.4 |
| 10% Ca(OH)2
|
33.6 |
42.2 |
37.9 |
| Fermented
molasses |
37.1 |
45.0 |
41 |
| |
|
|
|
| Means |
29.8 |
36.5 |
|
|
SEM ".26; P=.001 for MUB
SEM ".58; P=.001 for leaf
treatments
Results and discussion
The mean values for degradabilities (48h incubation) of the
leaves are set out in table 2.
All the chemical pre-treatments increased the degradability of
both dry matter and nitrogen compared with the control (P=.001).
As in Experiment 1, the rumen degradabilities were higher in the
steers having access to the molasses-urea blocks. The highest dry
matter degradability was with the fermented molasses treatment
which was superior by 62% compared with the control for +MUB and
by 58% for -MUB. Corresponding improvements for N degradability
were even higher at 89 and 103%, respectively. There were linear
increases in degradability of both dry matter and N as the
concentration of NaOH, or urea, increased in the treatment media.
| Table 3:
Effect of pre-treatment of Acacia mangium leaves
and of supplementing with molasses-urea block the host
(incubator) animal on rumen degradability of leaf
nitrogen |
|
| |
-MUB |
+MUB |
Means |
|
| Control |
17.0 |
20 |
18.5 |
| 2% NaOH |
20.7 |
24.2 |
22.5 |
| 3% NaOH |
20.9 |
25.8 |
23.3 |
| 6% NaOH |
23.7 |
28.2 |
25.9 |
| 9% NaOH |
23.8 |
30.1 |
26.9 |
| 3% Urea |
26.8 |
30.1 |
28.4 |
| 6% Urea |
29.3 |
32.6 |
31.0 |
| 9% Urea |
31.6 |
33.6 |
32.6 |
| 10% Ca(OH)2
|
32.1 |
35.1 |
33.6 |
| Fermented
molasses |
34.5 |
37.7 |
36.1 |
| |
|
|
|
| Means |
26.6 |
29.7 |
|
|
SEM +/-.39; P=.001
for MUB
SEM +/-.87; P=.001 for leaf
treatments
Conclusions
The experimental findings support the hypotheses that the
rumen degradability of leaves of Acacia mangium is low and
that this can be improved markedly by chemical pre-treatment,
especially Ca(OH)2 and acetic acid (the main product
of the fermentation of molasses).
It is tempting to conclude that the reduced degradability in
the lowermost leaves of the Acacia mangium tree reflected
increased concentrations of secondary plant compounds as a
biological defense mechanism against animal or human predators.
Acknowledgements
The authors are grateful to the Rector of the University of
Agriculture and Forestry, Ho Chi Minh City for providing the
facilities for this work and to the SAREC project S/2 VIE 22 for
financial support.
References
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