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Quack Grass (Agropyron repens L.): As Ruminant Feed

Naser Maheri-Sis, Afshar Mirzaei-Aghsaghali, Amir Reza Safaei, Ali Mirza-Aghazadeh and Ghassem Habibi Bibalani
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The nutritive value of quackgrass (Agropyron repens L.) was evaluated at late maturity. Rumen mixed microbe inoculums were taken from two fistulated Gezel rams. Samples of quackgrass were incubated with rumen fluid to determine gas production. Gas production was measured at 2, 4, 6, 8, 12, 24, 48, 72 and 96 h. The results showed that the Crude Protein (CP), Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF) content of quackgrass hay were 8.9, 69.5 and 38.3%, respectively. Organic Matter Digestibility (OMD) and Metabolizable Energy (ME) content were 43.54% and 6.58 MJ kg1 DM, respectively. In conclusion, it seems that quackgrass could be used as an efficient ruminant feed.

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Naser Maheri-Sis, Afshar Mirzaei-Aghsaghali, Amir Reza Safaei, Ali Mirza-Aghazadeh and Ghassem Habibi Bibalani, 2008. Quack Grass (Agropyron repens L.): As Ruminant Feed. Research Journal of Environmental Sciences, 2: 228-233.

DOI: 10.3923/rjes.2008.228.233



Weeds are troublesome in many ways. They reduce yield by robbing crops of water, light space and soil nutrient. Weeds can replace desirable grass species, filling in gaps or voids and reducing yield and overall quality of pasture and forages. Weeds can produce allelopathic substances that are toxic to crop plants (Bosworth et al., 1985). Quackgrass (Agropyron repens L.) is a perennial weed that competes aggressively with cereal and forage crops. Graminicides such as sethoxydim and fluazifop are used to control quackgrass in alfalfa stands but not in established forage grass stands due to lack of selectivity. Thus, producers renovate their fields because of quackgrass infestation (Christen et al., 1990). Although quackgrass has been used in ruminant feeding (Narasimalu et al., 1989; Christen et al., 1990) information on its nutritive value is limited. In goats, Dutt et al. (1979) estimated apparent digestibilities of DM and CP to be 57.1 and 67.7%, respectively, for alfalfa infested with 78 % quackgrass. These values increased to 61.4 and 75.5%, respectively, when the percentage of quackgrass infestation was decreased to 35% using pronamide as an herbicide. In beef cattle, Stoszek et al. (1979) reported that quackgrass resulted in higher average daily gain than did tall fescue. Narasimalu et al. (1989) found that quackgrass infestation of timothy did not affect silage composition, voluntary intake or apparent digestibility in sheep.

Since using chemical compounds resulted in air, water, soil and plant pollution, using biological methods for reducing weeds such as quackgrass was preferred. There are a few studies on quackgrass as a potential feedstuff for ruminants (Stoszek et al., 1979; Narasimalu et al., 1989; Christen et al., 1990), thus further studies would be useful.

The aim of this study was to determine the nutritive value of quackgrass (QCK) hay including chemical composition, in vitro gas production characteristics, organic matter digestibility and metabolizable energy.


The quackgrass (Agropyron repens) used for this study was collected near Karaj, Iran and evaluated at the laboratory of Animal Science Research Institute, Karaj, Iran in 2006. Forage, was harvested at late maturity. Samples were collected, air-dried and ground (1 mm screen) for chemical analysis and in vitro gas production (Kamalak et al., 2005a).

Chemical Analysis
Dry Matter (DM) was determined by drying the samples at 105°C overnight and ash by igniting the samples in muffle furnace at 525°C for 8 h and Nitrogen (N) content was measured by the Kjeldahl method (AOAC, 1990). Crude Protein (CP) was calculated as N x 6.25. Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Acid-Detergent Lignin (ADL) and Acid Insoluble Ash (AIA) were determined by procedures outlined by Goering and Van Soest (1970) with modifications described by Van Soest et al. (1991); sulfite was omitted from NDF analysis. Hemicellulose and cellulose were calculated as (NDF-ADF) and (ADF-ADL-AIA), respectively (Andrighetto et al., 1993). Gross Energy (GE) was measured in an adiabatic bomb calorimeter.

In vitro Gas Production
Fermentation of QCK hay samples were carried using rumen fluid obtained from two fistulated Gezel rams (1.5 years old, avg initial BW 55 kg) fed twice daily with a diet containing alfalfa hay (60%) and concentrate (40%) following the method described by Menke and Steingass (1988). Approximately 200 mg hay sample was weighed into the glass syringes of 100 mL. The fluid-buffer mixture (30 mL) was transferred into the glass syringes of 100 mL. The glass syringes containing hay samples and rumen fluid-buffer mixture were incubated at 39°C. The syringes were gently shaken 30 min after the start of incubation. The gas production was determined after 2, 4, 6, 8, 12, 24, 48, 72 and 96 h of incubation. All samples were incubated in triplicate with three syringes containing only rumen fluid-buffer mixture (blank). The net gas productions for hay samples were determined by subtracting the volume of gas produced in the blanks. Gas production data were fitted to the model of Ørskov and McDonald (1979).

Y = a + b (1–e-ct)


a = The gas production from the immediately soluble fraction (mL),
b =

The gas production from the immediately insoluble fraction (mL),

c =

The gas production rate constant for the insoluble fraction (%/h),

a + b =

Potential gas production (mL),

t = Incubation time (h),
Y =

Gas production at time t.

The ME (MJ kg-1 DM) content of QCK hay samples were calculated using equation of Menke et al. (1979) as follows:

ME (MJ kg-1 DM) = 2.20 + 0.136 GP + 0.057 CP


GP = Twenty four hour net gas production (mL/200 mg),
CP =

Crude protein (%).

Organic Matter Digestibility (OMD) (%) of QCK hays samples were calculated using equation of Menke et al. (1979) as follows:

OMD (%) = 14.88 + 0.889 GP + 0.45 CP + 0.0651 XA


GP = Twenty four hour net gas production (mL/200 mg),
CP =

Crude protein (%),

XA = Ash content (%).

In vitro gas production measurements were carried out in the laboratory of Animal Science Research Institute in Karaj.


The chemical composition of QCK hay is presented in Table 1. The CF content of QCK hay was 34.3%, while the ADF, NDF and ADL contents were 38.3, 69.5 and 5.7%, respectively. NDF value for QCK hay was similar to the value 66.4 found by Marten et al. (1987). Stoszek et al. (1979) estimated that ADF content for immature QCK was 34.1% and this value for QCK was lower than the value at 38.3% obtained in this experiment. NDF content was correlated positively with ADL and the ADL/ADF ratio, suggesting that as the plant matured lignification of cell walls increased (R = 0.93, p<0.06; R = 0.95, p<0.05, respectively). It was well established that the cell wall content of forages increase with increasing maturity (Gulsen et al., 2004; Kamalak et al., 2005b, c). Crude protein for QCK was 8.9%, a value lower than 14.5% reported by Stoszek et al. (1979) for immature QCK and of 17.2% reported by Marten et al. (1987) for common QCK harvested at joint.

The NFC and NFE values were 8.96 and 66%, respectively. The ash content, which is an index of mineral contents, was 11.2% in QCK hay. Cellulose (CE) and Hemicellulose contents were 32.6 and 31.1% in QCK hay, respectively. The lignification index (Table 1), on either NDF or ADF basis (Van Soest, 1982), in QCK hay was 8.1 and 14.6 %, respectively. The GE content for QCK hay was 4285.1 kcal kg-1.

Table 1: Chemical composition, fiber component and gross energy content of Quackgrass (QCK) hay
Image for - Quack Grass (Agropyron repens L.): As Ruminant Feed
QCK = Quackgrass; the data are mean value of three replicate; Non-fibrous carbohydrate (NFC) is calculated using the equation of NRC (2001), NFC% = 100 – (%NDF + %CP + % FAT + % Ash); NFE = Nitrogen-free extract; ADL = Acid-detergent lignin; AIA = Acid insoluble ash; ADL/NDF = Lignification index based on NDF; ADL/ADF = Lignification index based on ADF. GE = Gross Energy; SD = Standard Deviation

Table 2: Organic matter digestibility, gas production (mL) and estimated parameters of QCK hay at different incubation times
Image for - Quack Grass (Agropyron repens L.): As Ruminant Feed
a = The gas production from the immediately soluble fraction (mL); b = The gas production from the immediately insoluble fraction (mL); c = The gas production rate constant for the insoluble fraction (%/h); (a + b) = Potential gas production (mL); OMD = Organic matter digestibility (% of DM); ME = Metabolizable energy (MJ kg-1 DM), SD for OMD = 0.28 and for ME = 0.06 RSD of total incubation times = 1.865

Gas production data during the fermentation period are shown in Table 2. The cumulative volume of gas production increased with increasing time of incubation. Gas production at 96 h incubation was 52.4 mL per 200 mg of dry matter for QCK. Therefore the estimated parameters a, b, c and (a + b) of QCK hay were -0.95, 56.3, 0.035 and 55.35 mL, respectively.

In vitro gas production was measured at 2, 4, 6, 8, 12, 24, 48, 72 and 96 h following the describe kinetics of fermentation using the modified exponential model y = a + b[(1 – Exp(-ct)] (Ørskov and McDonald, 1979). Although there are other models available to describe the kinetics of gas production, the Ørskov and McDonald (1979) was chosen because the relationship of its parameters with intake, digestibility and degradation characteristic of forages and concentrate feedstuffs had been documented (Blummel and Ørskov, 1993; Khazaal et al., 1993).

The value for a, intercept, in QCK hay was negative in this study. These data suggested that a lag phase due to delay in microbial colonization of the substrate occurred in the early stage of incubation. Several authors (Menke et al., 1979; Blummel and Ørskov., 1993) have also reported negative values with various substrates when using mathematical models to fit gas production kinetics. The soluble fraction makes it easily attachable by ruminal microorganisms and this leads to much gas production (Khazaal et al., 1993; Blummel and Becker, 1997).

The gas volumes at asymptote (b) described the fermentation of the insoluble fraction and this was 56.3 mL in QCK hay. The gas volumes at asymptote have the advantage for predicting feed intake. Blummel and Ørskov (1993) found that gas volume at asymptote could account for 88% of variance in intake.

Rate of gas production (c) expressed in %/h, was 0.035. High rate of gas production possibly influenced by carbohydrate fractions that readily available to the microbial population. Deavill and Givens (2001) reported that carbohydrate fraction could affect kinetics of gas production.

Potential extent of gas production (a+b) expressed in mL, was 55.35% in QCK hay. It is well known that gas production is basically the result of fermentation of carbohydrates to acetate, propionate and butyrate (Getachew et al., 1998), whereas, protein fermentation do not lead to much gas production (Khazaal et al., 1995). However, the potential extent of gas production in QCK hay was low, possibly due to the carbohydrate fraction of QCK hay which has a large proportion of cell walls (Table 1) with low fermentation and leading to low gas production.

The OMD and ME contents of QCK were 43.54% of DM and 6.58 MJ kg-1 DM, respectively. The current finding agrees with studies on the nutritive value of pure QCK and timothy (Christen et al., 1990). The decrease in digestibility was due to increase in concentration of cell wall contents (Wilson et al., 1991), lignin content in mature plant (Morrison, 1980) and decrease in leaf/stem ratio (Hides et al., 1983). Menke et al. (1979) suggested that gas volume at 24 h after incubation has relationship with metabolisable energy in feedstuffs. Sommart et al. (2000) reported that gas volume is a good parameter from which to predict digestibility, fermentation end product and microbial protein synthesis of the substrate by rumen microbes in the in vitro system. Additionally, in vitro DM and OM digestibility were shown to have high correlation with gas volume (Sommart et al., 2000). Gas volumes also have shown a close relationship with feed intake (Blummel and Becker, 1997) and growth rate in cattle (Blummel and Ørskov, 1993).


The results of the current study based on chemical composition, digestibility of organic matter and metabolizable energy indicated that quackgrass could be a fair to good forage in ruminant nutrition. In addition, using weeds such as quackgrass in ruminant nutrition could reduce the use of chemical and toxic compounds (graminicides)which are usually used for controlling weeds in farms and therefore decreasing air, water, soil and plants pollution.


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