Effects of Electron Beam Irradiation on Dry Matter Degradation of Wheat Straw in the Rumen
The effect of electron beam irradiation at doses of
100, 200 and 300 kGy on ruminal dry matter degradation kinetics of wheat
straw was investigated. Samples were irradiated by electron beam irradiator
under identical conditions of temperature and humidity. Nylon bags of
untreated or irradiated wheat straw were suspended in the rumen of three
Taleshi steers for up to 96 h and resulting data were fitted to non-linear
degradation model to calculate degradation parameters of dry matter. Results
show that the washout fractions of dry matter increased linearly (p<0.001),
but potentially degradable fraction and degradation rate decreased linearly
(p<0.001) by electron beam irradiation. As a consequence, the effective
degradability of dry matter increased linearly (p<0.001) with increasing
irradiation dose. Electron beam irradiation at doses of 100, 200 and 300
kGy increased the effective degradability of dry matter at rumen outflow
rate of 0.05/h by about 7, 15 and 18%, respectively. In the condition
of this study, electron beam irradiation at dose of 200 kGy appeared to
be a suitable dose for improving dry matter degradability of wheat straw
in the rumen.
The huge production of the high fiber materials represents
an excellent potential resource for increasing ruminant production in
under-developing countries. The limitation for introducing this cheap
source of feedstuffs into animal diets is the presence of lignocellolosic
materials which have low digestibility (Al-Masri and Zarkawi, 1994). Physical
and chemical processing methods have been used to improve ruminal digestibility
of these materials. Processing such as grinding, steam treatment, irradiation,
sodium hydroxide, ammonia and biological applications have been used to
breakdown the lignocellulosic materials of agricultural residues and to
improve their nutritive value (Yu et al., 1975; Brownell and Saddler,
1987; Al-Masri and Zarkawi, 1994;Banchorndhevakul, 2002; Arora et al.,
2002; Jafari et al., 2007; Sadeghi and Shawrang, 2007a, b). The
application of irradiation on dry matter and cell-wall constituents of
some agricultural residues has been reported in the literature (Al-Masri
and Zarkawi, 1994). In cellulose industry, the effects of gamma and electron
beam irradiation on degradation of cellulose were widely investigated
in the past mainly with the aim of enhancing the enzymatic hydrolysis
(Takacs and Wojnarouits, 1999; Kuczumow et al., 1999). Recently,
Sadeghi and Shawrang (2007a, b) reported that electron beam irradiation
is effective on ruminal degradation of cell wall constituents of straws
and sugarcane bagasse.
As far as we know, there is limited information concerning
effects of electron beam irradiation on ruminal degradation kinetics of
cereal straws used in ruminant nutrition. Therefore, our purpose of this
study was to investigate the effect of electron beam irradiation on ruminal
dry matter disappearance characteristics and degradability parameters
of wheat straw.
MATERIALS AND METHODS
Sample preparation and irradiation treatments: This study was
conducted from December 2006 to June 2007. The wheat straw samples were
collected from five farms in Kerman-shah province of Iran. Samples were
mixed and air dried for 48 h and stored in seal plastic bags. The dry
matter of wheat straw was determined in an oven at 105C for 24 h before
of the irradiation treatments. The TT200 Rhodotron accelerator
was used for irradiation treatments of samples. The irradiation was accomplished
in the Yazd irradiation processing center (Atomic Energy Organization
of Iran). All samples were irradiated at a fixed beam energy of 10 MeV
(Kuczumow et al., 1999; Iller and Kukielka, 2002) and the required
irradiation doses were obtained by adjusting the electron beam parameters
(electron beam current, conveyor speed and etc.). Three polyethylene packages
of samples were electron beam irradiated at doses of 100, 200 and 300
kGy in the presence of air.
Animals and diets: Three Taleshi steers with an average live weight
of 400 kg fitted with rumen fistulas were placed in individual pens (3.4x4.9
m) with concrete floors that were cleaned regularly. Steers were fed 8
kg dry matter; a total mixed ration containing 700 g kg-1 of
dry matter of high quality alfalfa hay and 300 g kg-1 of dry
matter concentrate. The concentrate consisted of ground barley, soybean
meal, cottonseed meal, wheat bran, salt, dicalcium phosphate and vitamin
+ mineral premix (500, 160, 100, 210, 10, 10 and 10 g kg-1
dry matter, respectively). Diet was fed twice daily at 08:00 and 15:00
In sacco ruminal degradability: Nylon bags (9x21 cm) with
a pore size of 46 µm were filled with approximately 4.5 g of untreated
or irradiated wheat straw samples ground to pass 3 mm screen. All bags
were simultaneously placed in the rumen, just before the animals were
offered their first meal in the morning (i.e; 08:00 h). Bags were incubated
in the rumen for periods of 0, 6, 12, 24, 48, 72 and 96 h. After retrieved
from the rumen, bags were washed with tap water and stored at -20C. After
thawing, bags were washed three times for 5 min in a turbine washing machine.
The same procedure was applied to two series of two bags to obtain the
0 h value. All residues were oven dried (65C for 48 h) and dry matter
determined (Hvelplund and Weisbjerg, 2000).
Statistical analysis: Disappearances of dry matter were fitted
for each steer to the exponential model of Orskov and McDonald (1979)
as: p = a+b (1-e-ct). In this model, the constant a and b represent,
respectively, the washout fraction and the non-soluble but degradable
component, which disappears at a constant fractional rate c per unit time.
The effective degradability (ED) was calculated using ED = a+ bc/(c+k),
estimated outflow rates (k) of 0.02, 0.05 and 0.08 h (Agricultural and
Food Research Council, 1993). Data were analyzed using the general linear
models procedure of SAS (1996) with the following statistical model of
Yijk = µ + Ti + Bj + eijk, where, Y in the dependent variable, µ the overall
mean, Ti the electron beam effect, Bj the animal effect and eijk, is the
residual error, assumed normally and independently distributed. Differences
among treatments were separated using polynomial orthogonal contrasts
to determine linear, quadratic and cubic responses. The means comparative
of treatments was accomplished using Duncan`s multiple range tests (Steel
and Torrie, 1980).
RESULTS AND DISCUSSION
The percent of dry matter disappearance at different incubation
time increased as irradiation dose increased. The highest (p<0.05) disappearance
rate was for wheat straw samples exposed to 200 and 300 kGy electron beam
irradiation doses (Table 1).
Increasing electron beam irradiation dose, increased the
washout fraction (a) and decreased the potentially degradable fraction
(b) of dry matter (linear effect, p<0.001). The degradation rate of the
b fraction increased as irradiation dose increased (linear effect, p<0.001).
Effective degradability of dry matter linearly increased (p<0.001) as
irradiation dose increased (Table 2).
Dry matter disappearance (%)
of wheat straw
in different incubation periods
Means with the different superscripts
within column are differ (p<0.05)
||Rumen degradation parameters of dry matter of untreated
and electron beam irradiated wheat
|SEM: standard error of the means; L, linear contrast;
Q, quadratic contrast; C, cubic contrast.
Significance: NS, not significant; * p<0.05; ** p<0.01; *** p<0.001
a, the washout fraction, b, the potentially degradable fraction
and c the rate of degradation
Although, processing with gamma irradiation and other physical
processes have been occurred plentifully (Alberti et al., 2005;
Sadeghi and Shawrang, 2007a, b), however, with electron beam irradiation
has not been completely accomplished to improve the nutritive value of
the feedstuffs. Irradiation treatment (gamma rays) has been used as a
physical method to improve the nutritive value and digestibility of feedstuff
due to its effects on the peptide bonds (Shawrang et al., 2007)
and lignocellulosic bonds (McManus and Manta, 1972).
The organic matter digestibility as a result of gamma irradiation
increased for wheat straw with a clear decrease in the crude fiber and
NDF content (Yu et al., 1975). In a feeding experiment on wether
lambs fed with barley straw by a gamma ray dose of 370 kGy dose, disappearance
of NDF decreased and of dry matter increased (Al-Masri, 1997), significantly.
In addition, Pritchard and Pigden (1962) reported that the solubility
and digestibility of wheat straw increased by gamma irradiation. McManus
and Manta (1972) have indicated that an effect of irradiation on poor-quality
roughages (Lucerne straw and rice straw) given to sheep has started from
dose of 250 kGy. Han et al. (1981) reported that the dry matter
solubility of sugarcane bagasse irradiated with 500 kGy increased significantly.
In other experiments, the digestibility of organic matter and dry matter
degradability increased in wheat straw, cotton wood, olive cake and apple
pruning products after treatment with ?-irradiation (Al-Masri, 1997).
Recently, Sadeghi and Shawrang (2007b) reported that electron beam irradiation
at doses higher than 100 kGy could increase cell wall degradability of
straws and sugarcane bagasse in the rumen. In their study the effective
cell wall degradability of 50, 100, 200 and 300 kGy electron beam irradiated
sugarcane bagasse at rumen outflow rate of 0.05/h increased by 2, 13,
25 and 29%, respectively.
Under beam or gamma irradiation, cell wall constituents
may undergo degradation or cross-linking and at higher doses; degradation
predominates, which is more likely due to the splitting of the glucosidal
bond (Takacs and Wojnarouits, 1999). Therefore, electron beam irradiation
of cellulose or cellulose containing materials will lead to modification
in its structure. This modification may be due to several factors such
as consequences of unimolecularor bimolecular reaction of the radicals.
The beta cleavage of the radical can lead to the opening of the anhydroglucose
ring or breaking off the glucoside bond (Takacs and Wojnarouits, 1999).
It has been suggested that lignin is linked to both hemicellulose and
cellulose forming a physical seal around the latter two compounds that
is impenetrable barrier preventing penetration of solutions and enzymes
(Arora et al., 2002). The decrease of NDF and ADF of agricultural
residues by irradiation treatment could be the cause of degradation of
cellulose and hemicellulose into soluble materials (Banchorndhevakul,
2002). Finally based upon the results of this study, electron beam irradiation
appeared to be suitable for increasing dry matter degradation of wheat
straw in the rumen.
Authors are grateful to thank financial support of Atomic
Energy Organization of Iran (Dr. Shawrang design grant) and the Yazd irradiation
processing center for the irradiation operations. Also gratefully acknowledge
Mr. Fatholahi for assistance in irradiation treatment of samples, Mr.
Noori and Mrs. S.S. Mosavi for laboratory assistance. This study was obtained
from Ph.D Thesis of H.R. Shahbazi, Science and Research Branch, Islamic
Azad University, Tehran, Iran.
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