Effect of sodium hydroxide treatment of selected mature forages
E. Hatungimana1, D. W. Kellogg1, K. S. Anschutz1, and A. H. Brown, Jr.1
Story in Brief
Low digestibility of roughage limits ruminant performance. The objective of this experiment was to evaluate in vitro degradability of
selected mature forages including bermudagrass, crabgrass, tall fescue, eastern gamagrass, switchgrass, johnsongrass, and sweet sorghum
when treated with sodium hydroxide. Samples of forages were harvested late in the growing season during 2008, and dry matter yield
was calculated from field replicates. Samples were pre-treated with 0, 2, 4, and 6% sodium hydroxide for 24 h. Then, in vitro dry matter
disappearance was determined in duplicate. The concentrations of crude protein, neutral detergent fiber, and acid detergent fiber varied
among forages. Compared to no pretreatment, vitro dry matter disappearance was improved with sodium hydroxide. With 4% sodium
hydroxide treatment means were 61.1% for sweet sorghum, 44.3% for crabgrass, 52.4% for bermudagrass, 46.8% for eastern gammagrass,
48.4% for johnsongrass, 47.0% for tall fescue and 45.5% for switchgrass. Treatment with sodium hydroxide was more effective in forages
with greater neutral detergent fiber.
Introduction
Cellulose and hemicellulose constitute the major fibrous
components of grass. In low-quality forages carbohydrates are
associated with lignin and other compounds that make the fiber
less available to microorganisms in the intestinal tract, decrease
the rate and extent of digestibility and reduce animal performance
(Darcy and Belyea, 1980). Even high-quality forages have greater
concentrations of fiber at maturity compared to earlier in the growth
phase. The fiber of mature plants is slowly and incompletely digested
by microorganisms and limits energy intake by ruminant animals.
Switchgrass has been proposed as a cash crop for biomass that
could be used to produce ethanol. Lignification of cellulosic biomass
is also a problem for research on ethanol production from plant
materials such as switchgrass because more dry matter (DM) would
be available at maturity (Schroeder, 1996). Chemical treatment has
been used to break bonds between lignin and hemicelluloses or
cellulose, and sodium hydroxide (NaOH) has efficiently improved
digestibility of fibrous roughages (Klopfenstein, 1979).
The objective of this experiment was to pre-treat with NaOH
to determine the effects on in vitro digestibility of selected mature
forages.
Materials and Methods
Selected mature forage samples of bermudagrass (Cynodon
dactylon (L.) Pers.), crabgrass (Digitaria ciliaris), eastern gamagrass
(Trypsacum dactyloides (L.) L.), johnsongrass (Sorghum halepens (L.)
Pers.), sweet sorghum (Sorghum bicolor (L.) Moench), tall fescue
(Lolium arundinaceum Schreb.), and switchgrass (Panicum virgatum
L.) were harvested late in the 2008 growing season at the University of
Arkansas Experiment Station in Fayetteville. Fields were divided into
4 quadrants and a ¼-m2 frame was used to sample randomly or, when
appropriate, plants in 1-meter of row was selected randomly. The
height of plants was measured and the area was clipped to provide 3
replicates in each quadrant. Samples were weighed and dried under
forced air at 50 °C to determine field DM composition. Samples were
composited over field replications before laboratory analyses.
Pretreatment was conducted in 50-mL test tubes, in triplicate,
using different concentrations of NaOH (0, 2, 4 and 6%) by adding
1
2 mL of distilled water or diluted NaOH to 0.25 g of each forage
subsample. Treated material was held at room temperature for 24 h
to allow reaction.
Ruminal fluid was collected from a rumen-fistulated heifer
maintained on alfalfa hay and a corn-based supplement with ad
libitum access to water. After dilution with the buffer-nutrient
solution, 30 mL of ruminal fluid was added to each tube of the
pretreated samples. Duplicate tubes were placed in a 39 °C water bath
for different incubation times (0, 3, 6, 12, 24, 48 and 72 h). After each
time of incubation, tubes were removed from the water bath and
placed in a freezer. At a later time, materials were thawed and filtered
with filter paper. The residue was retained on the filter paper and was
sealed to be dried in an oven at 100 °C for 8 h after which samples
were weighed to determine the extent of degradability (IVDMD).
Means and standard deviations were calculated for the field data
and nutritive values of the forages. For the IVDMD experiment, a 7
× 4 × 7 factorial arrangement was used for 7 forages types, 4 NaOH
concentrations, and 7 in vitro incubation times. Data were analyzed
using GLM procedures of SAS version 9.1 (SAS Institute Inc., Cary,
N.C.) with the 3-way interaction used as error term. Both 2-way
interactions involving NaOH were significant (P < 0.01) suggesting
re-running the analysis by NaOH concentrations. Then a 7 × 7
factorial was used for each NaOH concentration with the 2-way
interaction of forage by time being the error term.
Results and Discussion
The results of plant height, DM content, forage yield and nutritive
value (composition of crude protein (CP), ash, neutral detergent fiber
(NDF), acid detergent fiber (ADF), acid detergent lignan (ADL),
and fat) are presented in Table 1. The height of plants ranged from
47.0 cm for bermudagrass to 343.5 cm for sweet sorghum. Forages
were all harvested near the end of the growing season. Data for DM
content of fall fescue was lost, so it was not possible to calculate DM
yield. It would appear that the tall growing plants (sweet sorghum
and switchgrass) provided the most DM yield and would be more
attractive to harvest for biomass conversion into sugars. However, the
composition of the plants may impact that decision.
Table 1 shows that CP content ranged from 4.9% in switchgrass
to 13.5% in bermudagrass. Eastern gamagrass and switchgrass had
the greatest NDF percentage, although all forages tested were above
University of Arkansas System Division of Agriculture, Department of Animal Science, Fayetteville, Ark.
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AAES Research Series 597
70% NDF except sweet sorghum. The plant composition of ADF
ranged from 26.1% in sweet sorghum to 43.1% in switchgrass.
Acid detergent lignin ranged from 2.3% in sweet sorghum to 5.5%
in eastern gamagrass. In this experiment, sweet sorghum had the
least percentage of NDF, ADF and ADL. Other forage species used
in this experiment had a greater fiber content, and this predicts low
digestibility of those forage species without pretreatment. Switchgrass
had the greatest concentrations of NDF and ADF. The energy content
of forages ranged between 4441 calories/g for switchgrass and 3779
calories/g for crabgrass.
Table 2 shows that the IVDMD of forages depended on the species
(P < 0.01), different time of incubation (P < 0.01), and concentration
of NaOH treatment used (P < 0.01). Significant interactions were
observed between forages and NaOH treatment (P < 0.01) and
between NaOH treatment and incubation time (P < 0.01). An
interaction between forages and incubation time was not detected (P
> 0.10). The IVDMD of all forages increased (P < 0.01) with longer
incubation time.
There was an interaction between forage and concentration
of NaOH treatment. Treatment of forages with 2 and 4% NaOH
(Table 3) increased IVDMD for all forages, but treatment with 6%
NaOH decreased IVDMD of some forages, probably due to the
increased alkalinity (pH = 7.6 to 7.8) after samples were treated with
6% NaOH. Although the solubilization of hemicelluloses should
have been greater with 6% NaOH treatment, the accumulation of
fermentation end products should have also impaired microbial
attachment in the first hours of incubation and reduced digestibility
(Arisoy, 1998). Bermudagrass, switchgrass, tall fescue, and eastern
gamagrass responded better to the 4% NaOH treatment than other
forages (Table 3). Johnsongrass and sweet sorghum responded better
to the 2% NaOH better than other forages. Crabgrass responded
better to 6% NaOH treatment. Differences in response may have
been due to the chemical composition of the forage species.
In conclusion, NaOH treatment of forages improved IVDMD of
forages. Treatment with 4% NaOH offered improvement of IVDMD
compared to other concentrations of NaOH used in this experiment
142
for most of forages species. Forages with greater fiber content were
improved most, in terms of percentage units of increased IVDMD
over untreated controls. Despite the improved digestibility with
NaOH treatment, the elevated pH was a problem, especially in
samples treated with 6% NaOH. Further investigations are needed
to use high concentrations of NaOH without compromising the pH
environment of rumen microbes. Emphasis should be also placed on
techniques of removing end products from fermentation to allow
microbial attachment and enhance microbial activity.
Implications
Treatment of forages with sodium hydroxide is effective in
increasing invitro digestibility and could be used to increase the
digestibility or low quality forages; however, the high pH created by
higher concentrations of sodium hydroxide may adversely affect the
pH and environment of the rumen.
Acknowledgements
Thanks are expressed to Dr. Zelpha Johnson for assistance with
statistical analyses and to Drs. Charles P. West and Nilda R. Burgos of
Crop, Soil and Environmental Sciences Department.
Literature Cited
Arisoy, M. 1998. The effect of sodium hydroxide treatment on
chemical composition and digestibility of straw. Turk. J. Vet.
Anim. Sci. 22:165-170.
Darcy, K., and L. Belyea. 1980. Effect of delignification upon in vitro
digestion of forage celluloses. J. Anim. Sci. 51:798-803.
Klopfenstein, T. 1979. Chemical treatment of crop residues. J.
Anim. Sci. 46:841-848.
Schroeder, J. W. 1996. Quality forage for maximum production
and return. North Dakota State Univ. Agric. Ext. Serv. Publ. As-1117.
Arkansas Animal Science Department Report 2011
Table 1. Average height, field dry matter (DM) percentage, DM yield, and nutrient composition
of selected mature forages1.
Height,
Item
cm
Bermudagrass
Mean
47.0
SD
6.0
Field
DM, %
Yield,
kg/ha
CP,
%
Ash,
%
NDF,
%
ADF,
%
ADL,
%
Fat,
%
Gross
Energy,
calories/g
29.0
2.0
3909
1149
13.5
1.0
9.3
1.0
74.9
1.8
34.0
0.4
3.4
0.3
2.2
4231
Crabgrass
Mean
SD
95.0
8.0
33.6
2.6
7250
2400
8.9
0.7
7.7
0.7
72.5
1.1
39.3
0.7
4.8
0.4
1.5
3779
Tall fescue2
Mean
122.7
SD
8.9
---------
-----------
9.2
2.9
8.1
1.9
70.7
2.2
40.6
1.5
4.5
0.6
2.1
4103
Eastern gamagrass
Mean
164.9
SD
15.1
36.2
2.3
3160
914
8.6
3.0
7.5
0.2
77.6
1.6
40.6
2.5
5.5
3.5
1.5
3928
Johnsongrass
Mean
183.9
SD
43.3
34.6
0.35
11264
1516
8.1
0.9
7.1
0.3
72.9
1.2
41.9
0.8
4.0
0.2
1.6
4108
Sweet sorghum
Mean
343.5
SD
26.5
31.6
1.05
21603
2496
5.7
1.0
4.4
0.1
47.2
3.8
26.1
1.4
2.3
0.4
2.2
3972
Switchgrass3
Mean
-----
45.50
18180
4.9
3.8
77.2
43.1
4.6
1.9
4441
1
CP = Crude protein, NDF = neutral detergent fiber, ADF = acid detergent fiber, ADL = acid detergent lignin,
GE = gross energy.
2
Data for DM of fescue was lost.
3
Switchgrass samples were provided by Dr. Charles West (Crop, Soil and Environmental Sciences Department,
Fayetteville), and SD values were not available.
Table 2. Effect of forage type, incubation time, NaOH treatment and their interactions on in vitro dry matter
disappearance (IVDMD)1.
P -value
NaOH concentration
0%
2%
4%
6%
SE
Forage
Time
NaOH
NaOH
× Time
Forage
× NaOH
Forage
× Time
35.0
28.7
49.1
40.9
52.4
46.8
48.0
47.3
0.4
0.4
< 0.01
< 0.01
0.05
0.2
< 0.01
< 0.01
< 0.01
< 0.01
< 0.01
< 0.01
>0.1
>0.1
JG
34.9
46.1
48.4
39.3
0.3
< 0.01
0.002
< 0.01
< 0.06
< 0.01
>0.1
CB
TF
34.5
34.3
49.4
44.7
44.3
47.0
43.8
40.6
0.3
0.3
< 0.01
< 0.01
<0.01
0.04
< 0.01
< 0.01
< 0.01
< 0.01
< 0.01
< 0.01
>0.1
>0.1
SS
54.4
63.7 61.1 59.6
0.2
< 0.01 <0.01 < 0.01
< 0.01
< 0.01
< 0.01
< 0.01
SG
30.1
42.4 45.5 44.2
0.1
0.08 < 0.01
0.002
1
Mean digestibility of forages at different times of incubation (0, 3, 6, 12, 24, 48, and 72 h)
per NaOH concentrations (0, 2, 4, and 6%).
2
BG = bermudagrass, EGG = eastern gamagrass, JG = johnsongrass, CB = crabgrass, TF = tall fescue,
SS = sweet sorghum, SG = switchgrass.
>0.1
>0.1
Forages2
BG
EGG
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AAES Research Series 597
Table 3. Effect of forage type and NaOH treatment on in vitro dry matter
disappearance of forages2.
NaOH concentration
Forages2
BG
0%
2%
4%
6%
35.0b
49.2b
52.4b
48.0b
c
c
40.9
46.8
47.3bc
34.9b
46.1bc
48.4c
39.3e
CB
34.5b
49.4b
44.3e
43.8cd
TF
34.3b
44.7c
47.6cd
40.6de
SS
54.4a
63.7a
61.2a
59.6a
SG
30.1c
42.4c
45.5de
44.7bcd
EGG
28.7
JG
SE
cd
0.7
0.5
0.3
0.4
Means in the same column with different superscripts differ ( P < 0.01).
1
Mean digestibility of forages at different times of incubation
(0, 3, 6, 12, 24, 48, and 72 h) per NaOH concentrations.
2
BG = bermudagrass, EGG = eastern gamagrass, JG = johnsongrass, CB = crabgrass,
TF = tall fescue, SS = sweet sorghum, SG = switchgrass.
a, b, c, d, e
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